FLUX-assisted solid state bonding of metal sheets that have native oxides

Abstract

Systems, compositions, and methods for bonding materials into consolidated sheets are provided. For example, oxidized scrap metal can be roll-bonded into metal sheets that are substantially free of metal oxides without rigorous surface preparation or high temperatures. In some embodiments, oxides on the surfaces of the materials can be dissolved with flux, which is then removed, thereby enabling bonding at lower temperatures with minimal preparation. The removed flux, as slag, can then be collected and recycled by reapplying the flux onto a surface of the materials to produce metal sheets in a continuous process.

Description

Attorney Docket No.: MIT 26265 USPCT | 88212-432500SYSTEMS AND METHODS FOR FLUX-ASSISTED SOLID STATE BONDING OF METAL SHEETS THAT HAVE NATIVE OXIDES CROSS REFERENCE TO RELATED APPLICATION(S)

[0001] The present disclosure claims priority to and the benefit of U.S. Provisional Application No. 63 / 738,755, entitled “Systems and Methods for Solid State Bonding of Metal Sheets That Have Native Oxides,’’ filed on December 24, 2024, the content of which is incorporated by reference herein in its entirety.FIELD

[0002] The present disclosure relates to systems and methods for solid-state bonding of materials, and more particularly relates to systems and methods for flux-assisted roll-bonding of metal sheets having native oxide layers on surfaces of the sheets, including oxidized or rusted steel and stainless steel, with flux being able to dissolve oxide barriers to facilitate bonding without intensive surface preparation.BACKGROUND

[0003] Conventional steel processes involve ironmaking, steelmaking, rolling, and forming to eventually manufacture the product. After each of the rolling, forming, and product steps, a portion of the materials can be recycled, with the resulting materials being reintroduced into the ironmaking and steelmaking steps and processes. As a result, energy, carbon dioxide, and other overall costs have increased dramatically for ironmaking and steelmaking due to the increased expenditures needed to incorporate the recycled materials into these steps.

[0004] Use of scrap metal can reduce some of the above costs and improve the efficiency of one or more of the above-described processes, but its use has several shortcomings. For example, scrap metal can have native oxides formed thereon. These native oxides can create a barrier between base metals that prevents contact between adjoining pieces of steel, thereby resulting in sheets that have weak and / or irregular bonding patterns. In addition, the presence of native oxides can impact many bonding methods, such as forging, friction stir welding, ultrasonic welding, and / or extrusion, while also impacting sheet metal consolidation (SMC), which is based on roll-bonding. Further still, native oxide can have a limited material range by disqualifying rusty steel, stainless steel, and / or superalloys, for example, from SMC, thereby limiting its potential uses.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0005] Accordingly, there is a need for improved systems and methods for solid state bonding of metal sheets that have native oxides.SUMMARY

[0006] The presently disclosed embodiments generally relate to systems and methods for flux-assisted solid-state bonding of metal sheets having native oxide layers on surfaces thereof. In particular, the present application is directed to solid-state bonding of metal scraps by coating metal sheets with borax-based flux granules, then assembling, enclosing, and subjecting the sheets to preheating, rolling, and cooling. The flux can break down oxide layers, facilitating bonding without intensive surface preparation. Flux deposition amount and / or location can be optimized based on one or more parameters that can ensure thorough bonding without the trapping of flux, which can cause cracks and / or gaps to form in the consolidated sheets. Excess flux, in the form of slag, which is formed after flux reacts with the oxides, can be expelled, resulting in a strong, clean bond. This form of bonding can result in an energy-efficient, scalable solution for recycling and consolidating metal scraps, broadening material compatibility within existing recycling infrastructure. Such systems and methods enable the bonding of materials that are traditionally difficult to join, including oxidized or rusted steel and stainless steel, by dissolving oxide barriers through the application of flux during roll-bonding operations. These approaches provide an energy-efficient and scalable solution for recycling and consolidating metal scraps while broadening material compatibility within existing recycling infrastructure.

[0007] In accordance with some embodiments, the ability to dissolve oxides with flux during roll-bonding can present advantages in reduced energy consumption, decreased processing time, and lower costs compared to conventional bonding techniques that involve rigorous surface preparation or high temperatures. Moreover, allowing previously challenging metals to be joined in a solid state supports efficient recycling, aiding industries in meeting sustainability targets and reducing dependency on raw materials andwaste. Further still, being able to collect and recycle expelled slag can present advantages to the sustainability and circularity of metal production processes.

[0008] In an aspect, embodiments relate to a method of bonding a plurality of materials. The method includes applying a flux to a surface of at least one of a first material or a second material of a plurality of materials. The method further includes aligning the plurality of materials with respect to one another such that the flux is disposed between the first materialAttorney Docket No.: MIT 26265 USPCT | 88212-432500and the second material. The method further includes roll-bonding the plurality of materials by passing the plurality of materials between an opposed pair of rollers that deform the plurality of materials with respect to one another to form a consolidated metal sheet of the plurality of materials. The flux is applied continuously throughout roll-bonding.

[0009] One or more of the following features can be included. Aligning the plurality of materials can further include placing at least a portion of the first material on top of at least a portion of the second material. Adding the flux and rolling the plurality of materials can occur substantially simultaneously. The first material and the second material can each include a metal sheet having a native oxide layer on a surface thereof. The method can further include preheating the plurality of materials prior to rolling the plurality of materials. The plurality of materials can be preheated to a temperature at which the flux dissolves the native oxide layer to form a slag. The method can further include expelling the slag from between the first material and the second material to one or more edges of the solid state consolidated metal sheet during roll-bonding, collecting the expelled slag, and dissolving the collected slag in water to separate the flux from oxides, wherein the flux is water soluble and the oxides are not water soluble. The method can further include reapplying the separated flux to a surface of a subsequent metal sheet for a subsequent bonding operation. The native oxide layer can include one or more of Fe-based oxides, Al-based oxides, Cu-based oxides, Ni-based oxides, Cr-based oxides, Ti-based oxides, or Mn-based oxides.

[0010] The flux can include borax, and preheating the plurality of materials can include preheating to a temperature approximately in a range of about 700°C to about 1250°C. The flux can include one or more of anhydrous sodium metaborate, boric acid, silica, sodium silicate, sodium fluoride, potassium fluoride, calcium fluoride, sodium chloride, potassium chloride, or ammonium chloride. The flux can be applied as a saturated flux solution that is sprayed onto the surface of the at least one of the first material or the second material to form an even layer of flux upon drying. The flux can be applied at a flux surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2. A composition of the first material can be different from a composition of the second material. The metal sheets can include one or more of rusted steel, stainless steel, or a superalloy. The metal sheets can include oxidized scrap metal. The flux can be applied without substantial preparation of the surface of the at least one of the first material or the second material.

[0011] Roll-bonding can include imparting a thickness reduction approximately in a range of about 25% to about 80% on the plurality of materials. Roll-bonding can occur at a rollingAttorney Docket No.: MIT 26265 USPCT | 88212-432500speed approximately in a range of about 1 foot per minute to about 13 feet per minute. The method can further include adjusting one or more of an amount of flux applied to the at least one of the first material or the second material, or a location along the surface of the at least one of the first material or the second material to which the flux is applied based on one or more of sheet geometry, sheet composition, or concentration on the surface. Sheet geometry can include one or more of thickness, form factor, aspect ratio, flux surface density, processing temperature, reduction amount, or size distribution. The method can further include collecting the slag from the at least one of the first material or the second material and reintroducing the flux from the slag to the surface of the at least one of the first material or the second material. The method can further include dissolving the collected slag in a liquid to separate the flux from oxides bonded thereto. Roll-bonding can occur at a temperature of at least about 750 degrees Celsius. The method can further include finishing the solid state consolidated metal sheet.

[0012] In another aspect, embodiments relate to a consolidated metal sheet formed by the method of bonding a plurality of materials.

[0013] In another aspect, embodiments relate to a method of continuously producing a consolidated metal sheet. The method includes feeding a plurality of metal sheets having native oxide layers on surfaces thereof into a rolling apparatus. The method further includes applying a flux to one or more surfaces of each of the plurality of metal sheets as the plurality of metal sheets are fed into the rolling apparatus, wherein the flux is applied at a surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2. The method further includes heating the plurality of metal sheets to a temperature of at least about 700°C such that the flux dissolves the native oxide layers to form a slag. The method further includes passing the plurality of metal sheets between an opposed pair of rollers to deform the plurality of metal sheets and expel the slag from between the plurality of metal sheets. The method further includes collecting the expelled slag from edges of the consolidated metal sheet.

[0014] One or more of the following features can be included. The flux can include borax, and heating the plurality of metal sheets can include heating to a temperature approximately in a range of about 700°C to about 1250°C. The plurality of metal sheets can include one or more of 1000 series mild steel or 300 series stainless steel. Passing the plurality of metal sheets between the opposed pair of rollers can include imparting a thickness reduction approximately in a range of about 25% on the plurality of sheets to about 80% on theAttorney Docket No.: MIT 26265 USPCT | 88212-432500plurality of metal sheets. The method can further include dissolving the collected slag in water to separate the flux from oxides, wherein the flux is water soluble and the oxides are not water soluble. The method can further include reapplying the separated flux to surfaces of subsequent metal sheets fed into the rolling apparatus. Applying the flux can include spraying a saturated flux solution onto the surfaces of the plurality of metal sheets to form an even layer of flux upon drying. The plurality of metal sheets can have thicknesses approximately ranging from about 0.1 mm to about 20 mm. The native oxide layers can include one or more of Fe-based oxides, Ni-based oxides, Cr-based oxides, or Mn-based oxides. A rolling speed can be approximately in a range of about 1 foot / minute to about 8 feet / minute.

[0015] In another aspect, embodiments relate to a system for consolidating sheet metal. The system includes a consolidation portion configured to produce a product from a plurality of sheet metals. The system further includes a scrap metal adding portion configured to add scrap metal into the receiving cavity of the consolidation portion. The system further includes a flux adding portion configured to apply a flux to a surface of the plurality of sheet metals. The system further includes a roll bonding portion configured to roll bond the plurality of metal sheets using a plurality of rollers.

[0016] One or more of the following features can be included. The system can further include a collection portion configured to collect slag from the surface of the plurality of sheet metals. The flux adding portion can be configured to spray a saturated flux solution onto the surfaces of the plurality of metal sheets to form an even layer of flux upon drying. The flux adding portion can be configured to apply the flux at a surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2. The preheating portion can be configured to heat the plurality of metal sheets to a temperature approximately in a range of about 700°C to about 125O°C. The roll bonding portion can be configured to impart a thickness reduction approximately in a range of about 25% on the plurality of metal sheets to about 80% on the plurality of metal sheets at a rolling speed approximately in a range of about 1 foot per minute to about 13 feet per minute. The system can further include a flux recycling portion configured to dissolve the collected slag in water to separate the flux from oxides and to return the separated flux to the flux adding portion for reapplication to subsequent metal sheets.Attorney Docket No.: MIT 26265 USPCT | 88212-432500BRIEF DESCRIPTION OF DRAWINGS

[0017] This disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0018] FIG. 1A is a schematic illustration of one embodiment of the present disclosure having two metal pieces having oxide layers formed on surfaces thereof with flux granules deposited therebetween;

[0019] FIG. IB is a schematic illustration of the flux of FIG. 1 A beginning to interact with the oxide layers at an interface of the metal pieces;

[0020] FIG. 1C is a schematic illustration of the flux of FIG. 1 A having dissolved a portion of the oxide layers to form slag;

[0021] FIG. ID is a schematic illustration of an interface between the metal pieces of FIG.1 A that is substantially devoid of oxide with slag remaining disposed therein;

[0022] FIG. IE is a schematic illustration of the metal pieces of FIG. 1 A being fed through rollers to extract slag and promote bonding;

[0023] FIG. IF is a schematic illustration of a resulting consolidated metal sheet with an inset (i) showing a cross-sectional view of a bonded interface;

[0024] FIG. 2A is a perspective view of a first metal sheet having a surface with native oxides thereon;

[0025] FIG. 2B is a perspective view of the first metal sheet of FIG. 2A after flux granules have been deposited onto its oxidized surface;

[0026] FIG. 2C is a perspective view of a second metal sheet being deposited on top of the first metal sheet of FIG. 2B with flux granules distributed across its oxidized surface;

[0027] FIG. 2D is a perspective view of an assembly of the first metal sheet and a second metal sheet with flux disposed therebetween enclosed within an envelope, according to aspects of the present disclosure;

[0028] FIG. 2E is a perspective view of the slag extracted from the first and second metal sheets after preheating and rolling;|0029| FIG. 2F is a perspective view of a final bonded sample showing a consolidated metal sheet;Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0030] FIG. 3A is a perspective view of a heated sample positioned before a roller during flux-assisted solid-state bonding;

[0031] FIG. 3B is a perspective view of the sample of FIG. 3 A beginning to engage with the roller as deformation commences;

[0032] FIG. 3C is a perspective view of the sample of FIG. 3A in an intermediate stage of the rolling process;

[0033] FIG. 3D is a perspective view of the sample of FIG. 3A undergoing further deformation through the roller;

[0034] FIG. 3E is a perspective view of the sample of FIG. 3A at a final stage of the rolling process, with slag being expelled;

[0035] FIG. 4A is a magnified image showing a bonded interface of mild steel processed without flux;

[0036] FIG. 4B is a magnified image at a higher magnification of a region of the interface from FIG. 4A showing pores and oxide inclusions at the interface;

[0037] FIG. 4C is a magnified image showing a bonded interface of mild steel processed with flux, according to aspects of the present disclosure;

[0038] FIG. 4D is a magnified image at a higher magnification of a region of the interface from FIG. 4C showing smaller and more rounded pores at the interface;

[0039] FIG. 5A is a magnified image showing a bonded interface in stainless steel processed without flux;

[0040] FIG. 5B is a magnified image at a higher magnification of a region of the interface from FIG. 5A showing an elongated pore with sharp corners;

[0041] FIG. 5C is a magnified image showing a bonded interface in stainless steel processed with flux, according to aspects of the present disclosure;

[0042] FIG. 5D is a magnified image at a higher magnification of a region of the interface from FIG. 5C showing a rounded pore with smooth edges;

[0043] FIG. 6A is a data table comparing bonding characteristics for mild steel samples processed with and without flux; andAttorney Docket No.: MIT 26265 USPCT | 88212-432500

[0044] FIG. 6B is a data table comparing bonding characteristics for stainless steel samples processed with and without flux.DETAILED DESCRIPTION

[0045] Certain embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems, devices, related components (e.g., flux granules, metal sheets, rollers, furnaces, envelopes, and collection portions), and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Further, to the extent features, layers, sides, objects, steps, or the like are described as being "first," "second," "third," etc., and / or "lower," "upper," "middle," etc., such numerical and / or location ordering / identification is generally arbitrary, and thus such numbering can be interchangeable unless indicated or otherwise understood by those skilled in the art to not be interchangeable.

[0046] The figures provided herein are not necessarily to scale, although a person skilled in the art will recognize instances where the figures are to scale and / or what a typical size is when the drawings are not to scale. Further, to the extent that linear or circular dimensions or shapes are used or described herein, such dimensions are not intended to limit the types of shapes or sizes of such devices, components, etc. A person skilled in the art will recognize that an equivalent to such linear and / or circular dimensions or shapes can be easily determined for any geometric shape (e.g., references to widths and diameters being easily adaptable for circular and linear dimensions, respectively, by a person skilled in the art). While in some embodiments movement of one component is described with respect to another, a person skilled in the art will recognize that other movements are possible. Further, to the extent arrows are used to describe a direction a component can expand or move, these arrows are illustrative and in no way limit the direction the respective component can expand or move. A person skilled in the art will recognize other ways and directions for creating the desired tension or movement.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0047] Still further, in the present disclosure, like-numbered components of various embodiments generally have similar features when those components are of a similar nature and / or serve a similar purpose, unless otherwise noted or otherwise understood by a person skilled in the art. To the extent the present disclosure includes prototypes, mock-ups, bench models, or the like, a person skilled in the art will recognize how to rely upon the present disclosure to integrate the techniques, systems, devices, and methods into a product, such as consolidated metal sheets, recycled steel products, or metal composites formed from scrap metal. A number of terms may be used throughout the disclosure interchangeably but will be understood by a person skilled in the art. By way of non-limiting example, the terms "flux," "flux granules," and "flux material," can be used interchangeably to refer to a chemical composition or material that is used to remove oxides from a surface of a material. In addition, terms such as "roll-bonding," "rolling," and "roll bonding," can be used interchangeably to refer to the machine parts used to deform the metal materials. Further still, the term “slag” will be understood to refer to the substance that is formed when flux reacts or interacts with oxides, such as those on the metal sheets discussed in this disclosure. Lastly, the terms "metal sheets," "sheet metal," and "metal scraps" may be used interchangeably with one another to refer to the metal materials that are being combined to form a consolidated sheet metal. Moreover, it will be appreciated that although features may be discussed with respect to one embodiment within the present disclosure, these features can be applied to every embodiment of the present disclosure where such feature would be supported.

[0048] To the extent terms like "approximately," "about," and "substantially" are used herein, a person skilled in the art will appreciate the scope those words convey in the context of their usage. In the context of flux-assisted solid state bonding of metal sheets, obtaining a certain degree of flux surface density, temperature, deformation percentage, rolling speed, and / or alignment of metal sheets, among other positioning and the like, may be difficult, and thus use of terms like "approximately," "about," and "substantially" is intended to address this difficulty. A person skilled in the art will understand what constitutes how close a particular dimension or placement should be to still fall within the spirit of the quantification and description provided for herein. Even in instances where such terminology is not used, and a dimension or amount just includes the number or term (e.g., "parallel" is used instead of "substantially parallel"), a person skilled in the art will appreciate that, unless explicitly indicated otherwise, terms like "approximately," "about," and "substantially" are applicable toAttorney Docket No.: MIT 26265 USPCT | 88212-432500those dimensions and terms as well. The foregoing notwithstanding, a person skilled in the art will appreciate that terms like "approximately," "about," and "substantially" at least encompass dimensions, quantities, temperatures, percentages, and surface densities that are ±10%, 10°, etc. of the provided amount, or encompass dimensions that are ±5%, 5°, etc. of the provided amount, unless indicated otherwise or otherwise known to those skilled in the art. The present disclosure appreciates that a person skilled in the art, in view of the present disclosure, understands suitable placements for various features of the disclosed systems, devices, and methods, and related components of any of the same, and thus to the extent a particular temperature, flux amount, deformation percentage, or rolling speed is described, unless it is explicitly indicated that such parameter must be exact, a person skilled in the art will appreciate other parameters that are possible without impacting the overall system, device, or method.

[0049] The present disclosure provides systems and methods for solid state bonding of a plurality of materials, such as metal sheets, that have native oxide layers formed on surfaces thereof. Native oxides can form on scrap metal and create a barrier between base metals that prevents contact between adjoining pieces of metal, thereby resulting in sheets that have weak and / or irregular bonding patterns. The presence of native oxides can impact many bonding methods, such as forging, friction stir welding, ultrasonic welding, and / or extrusion, while also impacting sheet metal consolidation (SMC), which is based on rollbonding. Further, native oxides can limit material range by disqualifying rusted steel, stainless steel, and / or superalloys from SMC, thereby limiting potential uses of such materials in recycling and manufacturing operations.

[0050] A method of bonding a plurality of materi als according to the present disclosure can address challenges associated with bonding metals having oxide layers by dissolving oxides with a flux material during roll-bonding operations. Bonding metals with oxide layers can conventionally involve rigorous surface preparation or high temperatures, which can limit scalability and raise recycling costs. The flux-assisted process of the present disclosure can enable bonding at lower temperatures with minimal preparation of the metal surfaces. The flux-assisted process can allow recyclers to achieve effective metal bonding with reduced energy consumption, process time, and costs compared to conventionalapproaches. Moreover, the process can broaden material compatibility within existing recycling infrastructure by allowing previously challenging metals to be joined in a solidAttorney Docket No.: MIT 26265 USPCT | 88212-432500state. Materials that can be bonded using the flux-assisted process include oxidized or rusted steel, stainless steel, and superalloys, among other metals having native oxide layers. The ability to bond such materials can support efficient recycling, aiding industries in meeting sustainability targets and reducing dependency on raw materials while decreasing waste.

[0051] The flux-assisted solid state bonding process can involve applying flux to a surface of at least one material of a plurality of materials to be bonded. The flux can dissolve oxide layers present on the surfaces of the materials, thereby removing barriers that would otherwise prevent metal-to-metal contact during bonding. For example, in some embodiments, the plurality of materials can be aligned with respect to one another, e.g., formed in a stack, and heated to allow the flux to strip the surface oxides from the plurality of materials, which forms a slag. Once the oxide layers are stripped and slag is formed, the plurality of materials can be subjected to roll-bonding by passing the materials between an opposed pair of rollers that deform the materials. During roll-bonding, the slag can be expelled from between the materials, resulting in a strong, clean bond between the metal surfaces.

[0052] The flux-assisted process can be compatible with current scrap metal consolidation machinery, allowing seamless integration into manufacturing and recycling workflows. The process can reduce energy usage by enabling bonding at lower temperatures compared to conventional techniques that involve melting or extensive surface preparation. The flux-assisted process can also reduce processing time and costs by eliminating or minimizing the need for rigorous surface preparation prior to bonding. Benefits of the flux-assisted solid state bonding process can include enhanced productivity, reduced environmental impact from lower emissions, and improved recyclability of metal scraps, all of which can support a more sustainable, circular economy in metal production.

[0053] FIGS. 1A-1F illustrate a flux-assisted solid state bonding process 100 for metal sheets according to the present disclosure. As shown, the process 100 can involve adding flux 102 to a surface of at least one of a first material A or a second material B of a plurality of materials 104, aligning the plurality of materials 104 with respect to one another, and rollbonding the plurality of materials 104 by passing the plurality of materials 104 between an opposed pair of rollers 110 that deform the plurality of materials 104 with respect to one another. The flux 102 can be added continuously to form a solid state consolidated metal sheet of the plurality of materials, as discussed in greater detail below.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0054] In particular, referring to FIGS. 1A-1D, a progressive sequence of the bonding mechanism between two metal pieces labeled A and B is shown. FIG. 1 A illustrates two metal pieces A and B of the plurality of materials 104 having an oxide layer 106 formed on surfaces thereof. It will be appreciated that while pieces A and B are referred to as metal pieces throughout this disclosure, other materials are possible, such as aluminum, copper, nickel, steel, titanium, and their alloys. The oxide layers 106 can include native oxides that form on scrap metal and create a barrier between base metals that prevents contact between adjoining pieces of metal. The oxide layer 106 can be in the form of particles, as shown, though, in some embodiments, the oxide layer 106 can be a film, a coating, or the like.

[0055] One or more flux granules 102 can be deposited between the metal pieces A and B. As shown, the flux granules 102 can be deposited onto the oxide layers 106 to facilitate dissolution of the oxide layers during subsequent processing steps or onto the surface of the plurality of materials A and B. The flux 102 can be applied as an even layer using a saturated flux solution, which is sprayed on the surface of at least one of the metal pieces A or B. The saturated nature of the flux solution can create an even layer as appreciated by one skilled in the art, or a uniform layer, of flux upon drying, whereas an unsaturated solution would result in an uneven layer of flux that could decrease the efficacy of the flux in removing oxides. It will be appreciated that for the purposes of the present disclosure, an even layer of flux can, in some embodiments, include slight variations in size and / or amount of flux particles as compared to adjacent layers and / or layers at another location. For example, variations of up to about 20% in size of flux particles and / or up to about 20 wt% in amount of flux particles present between two locations along the surface of metal pieces A or B are still contemplated to fall within the scope of an even layer of at least some of the present embodiments. The distribution of flux 102 can be global rather than local across the surface of the metal pieces A and B to allow for thorough cleaning of surface oxidation. Adding the flux 102 to the surface of at least one of the first material A or the second material B can remove one or more oxides 106 from a surface of the plurality of materials.

[0056] FIG. IB illustrates the flux 102 beginning to interact with the oxide layers 106 as the materials are brought together. Aligning the plurality of materials A and B with respect to one another can include placing the first material A on top of the second material B, with the surface of at least one of the first material A or the second material B that includes the flux 102 being disposed between the first material A and the second material B. As shown inAttorney Docket No.: MIT 26265 USPCT | 88212-432500FIG. IB, the metal piece A can be positioned on top of the metal piece B with the flux granules 102 and oxide layers 106 disposed at an interface between the metal pieces A and B.

[0057] FIG. 1C illustrates the flux 102 having dissolved the oxide layers 106, with the flux material 102 visible amid slag, e.g., dark slag, 108 formed following a reaction with the oxides. That is, the flux 102 can react with the oxides 106 present on the surfaces of the metal pieces A and B to form slag 108, which can include a mixture of the flux material 102 and the dissolved oxide material 106. The dissolution of the oxide layers 106 by the flux 102 can expose clean metal surfaces on the metal pieces A and B, thereby enabling metal-to-metal contact during subsequent roll-bonding operations. It will be appreciated that the reaction between the flux 102 and the oxide layers 106 can occur once the plurality of materials 104 are heated, as discussed in greater detail below.

[0058] FIG. ID illustrates the substantially complete dissolution of the oxide layers 106. As shown, an interface 109 between the two metal pieces A and B is substantially devoid, or devoid of oxide, with slag 108 remaining disposed therein. With continued reference to FIGS. IE and IF, the roll bonding process is illustrated to facilitate direct contact between the metal surfaces of the metal pieces A and B, thereby enabling solid state bonding to occur at the interface 109. As shown, FIG. IE shows the metal pieces A and B being fed through the rollers 110 in a direction indicated by the curved arrows. Roll-bonding the plurality of materials 104 can include passing the plurality of materials 104 between an opposed pair of rollers 110 that deform the plurality of materials 104 with respect to one another.

[0059] The rollers 110 can apply compressive force to the metal pieces A and B to extract the slag 108, with the compressive force also causing deformation of the materials 104 and promoting bonding at the interface between the metal pieces A and B. For example, during roll-bonding, the remaining slag 108 can be expelled from the interface 109 between the metal pieces A and B. Expelling the slag 108 from the surface of the at least one of the first material A or the second material B to one or more edges of the at least one of the first material A or the second material B can occur as the rollers 110 deform the materials 124. The deformation imparted by the rollers 110 can provide a driving force to push the slag 108 away from the bond interface 109 and toward the edges of the consolidated sheet.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0060] FIG. IF illustrates the resulting consolidated metal sheet AB 120. As shown in the inset (i), a cross-sectional view of the bonded interface illustrates bonding and little to no crack formation therebetween, with the interface 109 between the first material A and the second material B showing no slag 108 remaining therein. The consolidated metal sheet AB can be formed as a solid state consolidated metal sheet of the plurality of materials through the flux-assisted roll-bonding process. The expulsion of the slag 108 during rolling can result in a strong, clean bond between the metal pieces A and B without trapped flux or oxide inclusions at the bond interface 109.

[0061] FIGS. 2A-2F illustrate a sequence of images showing a perspective view of the preparation and processing stages of metal sheets during the flux-assisted solid-state bonding process 100. FIG. 2A shows the first metal sheet A having a surface with native oxides 106, which can appear as a brownish oxidized or rusted surface. In some embodiments, the first material or first metal sheet A can include oxidized scrap metal having native oxide layers formed thereon without substantial preparation of the surface prior to flux application. The flux 102 can be added without substantial preparation of the surface of at least one of the first material A or the second material B, thereby reducing processing time and costs associated with rigorous surface preparation techniques.

[0062] FIG. 2B depicts the same first metal sheet A after granules of flux 102 have been deposited onto the oxidized surface. The white granular flux material 102 is visible distributed across the surface of the first metal sheet A. The flux granules 102 can be deposited onto the oxidized surface to facilitate dissolution of the oxide layers during subsequent processing steps. FIG. 2C shows the second metal sheet B, which can also include native oxides 106 thereon, being placed on the first metal sheet A, thereby sandwiching the flux granules 102 in between to form the plurality of materials or sample 104. It will be appreciated that, in some embodiments, the addition of the second metal sheet B can more evenly distribute the flux 102 across the oxidized surface. The even distribution of flux granules 102 across the surface can allow for thorough cleaning of surface oxidation during the bonding process.

[0063] Adjusting the location along the surface of at least one of the first material A or the second material B to which the flux is added can be based on one or more of sheet geometry, sheet composition, or concentration on the surface. The location of flux deposition can be varied based on the geometry of the metal sheets being bonded to ensure thorough coverageAttorney Docket No.: MIT 26265 USPCT | 88212-432500of the oxide layers and effective oxide dissolution across the entire bonded interface. The flux can be applied in an even layer across the surface of the metal sheets A and B to allow for thorough cleaning of surface oxidation.

[0064] Sheet geometry can include one or more of thickness, form factor, aspect ratio, flux surface density, processing temperature, reduction amount, or size distribution. The thickness of the metal sheets can affect the amount of deformation that can be imparted during roll-bonding and the ability to extrude slag from the bonded interface. The form factor and aspect ratio of the metal sheets can affect the distribution of flux across the surface and the pathways available for slag expulsion during roll-bonding. The processing temperature can affect the viscosity of the flux and the slag, which can influence the ability to extrude the slag during roll-bonding. The reduction amount can affect the driving force available to push the slag toward the edges of the consolidated sheet. The size distribution of scrap metal pieces can affect the porosity of the scrap stack and the amount of flux used to fill gaps and dissolve oxide layers.

[0065] FIG. 2D illustrates sheets A and B after the rust and / or native oxides 106 have been removed from the first and second sheets A and B. The first and second metal sheets A and B can appear as an orange or copper-colored layer following native oxide dissolution. The system for consolidating sheet metal can include an envelope, film, or enclosure system 111 configured to contain the assembled sheet metal pieces during preheating and processing. The envelope 111 can protect the assembled sheet metal pieces from oxidation during elevated temperature processing and can contain the flux during preheating to prevent loss of flux material before roll-bonding. The envelope 111 can be formed from metallic materials compatible with the processing temperatures and can be removed or opened prior to rollbonding to allow the sheet metal pieces to pass through the rollers, though, in some embodiments, the envelope 111 can be removed or opened after roll-bonding.

[0066] FIG. 2E shows the slag 108 that remains after preheating the sheets A and B to facilitate a reaction between the flux 102 and the native oxides 106, and rolling the first and metal sheets A and B. Preheating the assembled sample, e.g., first and metal sheets A and B, can elevate the temperature of the metal sheets A and B and the flux 102 to a processing temperature at which the flux 102 can become active and can dissolve the oxide layers 106 present on the surfaces of the metal sheets A and B to form the slag 108 as noted above. After rolling, the slag 108 can be extracted and contained within the film and / orAttorney Docket No.: MIT 26265 USPCT | 88212-432500envelope 111, indicating that the flux has reacted with and dissolved the oxide layers during the bonding process.

[0067] FIG. 2F depicts the final bonded sample, e.g., consolidated metal sheet 120 after processing, showing a consolidated metal sheet 120 with a uniform grayish appearance. The uniform appearance of the consolidated metal sheet 120 demonstrates successful solid-state bonding of the metal sheets A and B with the oxide layers 106 removed and excess flux 102 expelled from the bond interface 109 in the form of slag 108. The flux-assisted roll-bonding process can produce consolidated metal sheets having strong, clean bonds between the constituent metal sheets.

[0068] FIGS. 3A-3E illustrate a sequence of images showing the rolling process during flux-assisted solid-state bonding. The images capture the progression of a heated sample, such as an assembly of first and second metal sheets A and B shown in FIG. 2D, passing through a roller 110. FIG. 3 A shows the initial stage with the heated plurality of materials or sample 104 positioned before the roller 110, with a scale bar indicating one centimeter for reference. The heated sample 104 can be at a processing temperature suitable for flux activation and solid state bonding of the metal sheets A and B.

[0069] FIG. 3B depicts the sample 104 beginning to engage with the roller 110 as deformation commences. FIG. 3C shows the sample 104 in an intermediate stage of the rolling process, with the roller 110 applying compressive force to the heated material. The compressive force applied by the roller 110 can deform the metal sheets A and B and promote bonding at the interface 109 between the metal sheets A and B while simultaneously driving the slag 108 toward the edges of the sample.

[0070] FIG. 3D illustrates continued progression of the sample through the roller 110, with the material undergoing further deformation. FIG. 3E shows the final stage of the rolling process, where the slag 108 formed from the reaction between the flux and the dissolved oxides is visible being expelled from the sample 104 as indicated by an arrow inFIG. 3E. The expulsion of the slag 108 during rolling demonstrates the mechanism by which the flux-assisted process removes oxide layers and facilitates bonding between the metal sheets A and B to form the consolidated metal sheet AB, while simultaneously extruding the slag 108 from the bond interface.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0071] The slag 108 formed from the reaction between the flux 102 and the dissolved oxides 106 can exhibit viscous behavior that is dependent on time and temperature. For example, the flux viscosity can have temperature dependence, with the flux becoming thicker as the flux cools, which can affect extrusion behavior of the slag during rolling. As the slag 108 cools during the rolling process, the slag 108 can become more viscous and more difficult to extrude from between the metal sheets A and B.

[0072] The rolling speed can be chosen to provide sufficient time for the viscous slag 108 to flow toward the edges of the sample 104 and be expelled before the slag 108 solidifies or becomes too viscous to extrude. For example, in some embodiments, the rolling speed can be between about 1 foot / minute to about 8 feet / minute at laboratory scale. The rolling speed can be selected such that the viscous slag 108 has sufficient time to be extruded from the bonded interface based on the time-dependent flow response of the slag. Rolling speeds approximately within the range of about 1 foot / minute to about 8 feet / minute can provide sufficient time for the slag to flow toward the edges of the sample and be expelled before the slag solidifies or becomes too viscous to extrude. The rolling speed can be selected based on one or more of the processing temperature, the flux composition, and the viscosity characteristics of the slag to achieve effective slag expulsion.

[0073] In some embodiments, the rolling speed can be up to 13 feet / minute with appropriate force applied during roll-bonding. Higher rolling speeds can be achieved when greater compressive force is applied by the rollers, which can provide increased driving force for slag expulsion. The ability to achieve higher rolling speeds can depend on the rolling equipment capabilities and the force that can be applied to the metal sheets during rollbonding. Higher rolling speeds can increase the throughput of the flux -assisted solid state bonding process, which can improve productivity in industrial-scale applications.

[0074] Rolling speeds that are too fast, e.g., above these ranges, may not provide sufficient time for the slag to be extruded, which can result in slag inclusions trapped at the bond interface and poor bond quality. Rolling speeds that are too slow, e.g., below these ranges, may allow the slag 108 to cool excessively and become too viscous to extrude effectively. The rolling speed can be selected based on the processing temperature, the flux composition, and the viscosity characteristics of the slag to achieve effective slag expulsion and high-quality bonding.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0075] In some embodiments, adding the flux 102 and rolling the plurality of materials 104 can occur substantially simultaneously. It will be appreciated that for the purposes of the present disclosure, "substantially simultaneously" can refer to the flux 102 and rolling to occur with at least a single instance of a time overlap, though, in some embodiments, one or more of the addition of the flux and / or the rolling can be terminated for up to ten seconds, up to five seconds, up to three seconds, and / or up to one second, while the other of the addition of the flux and / or the rolling can continue. The flux 102 can be applied continuously as the metal sheets A and B are fed into the rolling apparatus 110, with the flux 102 being deposited onto the surfaces of the metal sheets A and B and the metal sheets A and B being consolidated through roll-bonding in a continuous process. The continuous process can allow for efficient production of consolidated metal sheets without the need for batch processing of individual samples. The flux 102 can be added continuously to form a solid state consolidated metal sheet 120 of the plurality of materials through the flux-assisted rollbonding process.

[0076] FIGS. 4A-4D illustrate a comparison of microscopy images showing bonded interfaces 109, 209 in mild steel with and without flux treatment. The plurality of materials 104 can include metal sheets A and B, and the metal sheets A and B can include oxidized scrap metal such as 1000 series mild steel. In particular, FIGS. 4A and 4B illustrate mild steel processed using conventional techniques, such as those without flux 102, while FIGS.4C and 4D illustrate mild steel processed with flux in accordance with the techniques discussed in the present disclosure.

[0077] Referring to FIG. 4A, a low magnification view at a 100 micrometer scale shows the bonded interface 109 of mild steel using conventional means, e.g.. without flux. A continuous dark line of trapped oxides 106 and irregularities is visible along the bond line 209 in FIG. 4A. The trapped oxides 106 can create banners between the base metals A and B that prevent contact between adjoining pieces of metal, thereby resulting in sheets that have weak and / or irregular bonding patterns. FIG. 4B provides a higher magnification view at a 10 micrometer scale of a region from FIG. 4 A, revealing large, irregularly shaped pores 212 and oxide inclusions trapped at the interface 209. The irregularly shaped pores 212 can have sharp corners that create stress concentration points where cracks can propagate during mechanical loading of the consolidated metal sheet.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0078] The addition of flux can result in pore rounding at the bonded interface 109, creating spherical pores 112 that are more resistant to cracking compared to sharp diamondshaped pores. The sharp diamond-shaped pores 212 observed in samples processed without flux, such as in FIGS. 4A-4B, can have sharp corners that act as stress concentration points. The stress concentration at sharp comers can promote crack initiation and propagation during mechanical loading of the consolidated metal sheet. FIG. 4C, for example, illustrates a low magnification view at a 100 micrometer scale shows the bonded interface 109a of mild steel with flux 102 of the present disclosure. The bond line 109a in FIG. 4C appears significantly cleaner with minimal visible defects compared to the interface 209 shown in FIG. 4A. FIG. 4D provides a higher magnification view at a 10 micrometer scale of a region of the interface 109 from FIG. 4C, showing smaller, more rounded pores 112a with substantially reduced or even eliminated oxide inclusions compared to the sample without flux shown in FIG. 4B. The spherical pores 112a created through flux-assisted bonding can have smooth edges that distribute stress more evenly, thereby reducing the likelihood of crack initiation and improving the mechanical performance of the consolidated metal sheet.

[0079] FIGS. 5A-5D illustrate a comparison of microscopy images showing bonded interfaces in stainless steel samples processed with and without flux. The metal sheets can include one or more of rusted steel, stainless steel, or a superalloy. The stainless steel samples 104 shown in FIGS. 5A-5D can include 300 series stainless steel, such as 304L stainless steel. FIGS. 5A-5B illustrate a sample 104 processed without flux using conventional techniques, while FIGS. 5C-5D illustrate the sample 104 processed with flux 102 in accordance with the techniques discussed in the present disclosure.

[0080] Referring to FIG. 5A, a low magnification view at a 20 micrometer scale shows a bonded interface 309 in stainless steel without flux. Elongated dark features and / or irregular voids are visible along the bond line 309 in FIG. 5A. The elongated features can represent trapped oxides and unbonded regions at the interface 309 between the stainless steel sheets. FIG. 5B provides a higher magnification view at a 2 micrometer scale of a region of the interface 309 from FIG. 5 A, revealing an elongated, irregularly shaped pore 312 with sharp corners characteristic of trapped oxides at the interface 309. The sharp corners of the elongated pore 312 can create stress concentration points where cracks can initiate and propagate during mechanical loading of the consolidated metal sheet.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0081] FIG. 5C illustrates a low magnification view at a 20 micrometer scale shows a bonded interface 109b in stainless steel with flux 102. Discrete rounded dark spots are distributed along the bond region in FIG. 5C, in contrast to the elongated features observed in FIG. 5A. FIG. 5D provides a higher magnification view at a 2 micrometer scale of a region of the interface 109b from FIG. 5C, revealing a single rounded pore 112b with smooth edges and a substantially circular cross-section. The rounded pore 112b shown in FIG. 5D demonstrates the pore rounding phenomenon that can occur when flux is used during the bonding process.

[0082] The pore rounding phenomenon observed in stainless steel samples processed with flux can result from the dissolution of oxide layers by the flux material 102. For example, as noted above, when oxide layers are dissolved by the flux 102, the flux 102 and dissolved oxides 106 can react to form slag 108 that is expelled during roll-bonding. The removal of the oxide layers can allow metal-to-metal contact between the stainless steel sheets, and any remaining pores at the interface can assume a more rounded morphology compared to the sharp, elongated pores observed in samples processed without flux.

[0083] The comparison between FIGS. 5A-5B and FIGS. 5C-5D demonstrates that the flux-assisted bonding process can produce improved bond quality in stainless steel samples. The transformation from sharp, elongated pores 212 to rounded pores 112b with smooth edges can improve the mechanical performance of consolidated stainless steel sheets by reducing stress concentration points at the bonded interface. The flux-assisted solid state bonding process can enable effective bonding of stainless steel, including 300 series stainless steel, without rigorous surface preparation prior to bonding.

[0084] A comparison between FIGS. 4A-4B and FIGS. 4C-4D demonstrates that the flux-assisted bonding process can result in improved bond quality with fewer and more rounded pores at the interface 109, 209. The reduction in pore density, the increase in pore roundness, the increase in average ligament length, and the increase in bonded fraction can all contribute to improved mechanical performance of consolidated metal sheets formed through the flux-assisted solid state bonding process. The flux-assisted process can enable effective bonding of oxidized scrap metal, such as 1000 series mild steel, without rigorous surface preparation prior to bonding.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0085] The addition of flux 102 can increase an average ligament length, which represents a bonded area between two pores 112a, at the bonded interface 109a. The increased average ligament length can indicate that the bonded regions between adjacent pores are larger in samples processed with flux compared to samples processed without flux. The addition of flux 102 can also increase an overall bonded fraction at the interface between the metal sheets A and B. The bonded fraction can represent a percentage of the interface area that is bonded between the metal sheets.

[0086] FIGS. 6A-6B illustrates such quantitative data comparing bonding characteristics for mild steel and stainless steel samples processed with and without flux. FIG. 6A presents data for mild steel samples of FIGS. 4A-4D and includes four measured parameters: average pore area in square micrometers, average pore density in number per millimeter, average ligament length in micrometers, and bonded seam fraction as a percentage, while FIG. 6B presents corresponding data for stainless steel samples of FIGS. 5A-5D processed. The quantitative data presented in FIGS. 6A-6B demonstrates the improvements in bond quality that can be achieved through the flux-assisted solid state bonding process.

[0087] Referring to FIG. 6A, for mild steel processed without flux, the average pore area is 6.01 square micrometers, the average pore density is 79.2 per millimeter, the average ligament length is 7.37 micrometers, and the bonded seam fraction is 59.2 percent. For mild steel processed with flux, the average pore area decreases to 1.29 square micrometers, the average pore density decreases to 46.6 per millimeter, the average ligament length increases to 16.8 micrometers, and the bonded seam fraction increases to 82.6 percent. The data in FIG. 6A demonstrates that flux addition can improve bonding quality in mild steel by reducing average pore area, reducing pore density, increasing average ligament length, and increasing bonded seam fraction. For example, larger ligament lengths can provide greater bonded area to resist mechanical loading and can improve the overall strength of the bond between the metal sheets. Moreover, a higher bonded fraction can indicate that a greater proportion of the interface is in direct metal-to-metal contact, which can improve the mechanical properties of the consolidated metal sheet. The flux-assisted bonding process can dissolve oxide layers that would otherwise prevent metal-to-metal contact, thereby increasing the bonded fraction at the interface.

[0088] The reduction in average pore area from 6.01 square micrometers to 1.29 square micrometers in mild steel samples processed with flux indicates that the pores 112aAttorney Docket No.: MIT 26265 USPCT | 88212-432500remaining at the bonded interface 109a are smaller when flux is used during the bonding process. Smaller pores can have less impact on the mechanical properties of a consolidated metal sheet compared to larger pores. The reduction in average pore density from 79.2 per millimeter to 46.6 per millimeter indicates that fewer pores are present along the bonded interface when flux is used, which can result in a more continuous bond between the metal sheets A and B.

[0089] The increase in average ligament length from 7.37 micrometers to 16.8 micrometers in mild steel samples processed with flux indicates that the bonded regions between adjacent pores are larger when flux is used during the bonding process. The increase in bonded seam fraction from 59.2 percent to 82.6 percent indicates that a greater proportion of the interface is in direct metal-to-metal contact when flux is used, which can improve the mechanical properties of a consolidated metal sheet formed through the flux-assisted solid state bonding process.

[0090] With continued reference to FIG. 6B, for stainless steel processed without flux, the average pore area is 0.22 square micrometers, the average pore density is 301.6 per millimeter, the average ligament length is 2.27 micrometers, and the bonded seam fraction is 68.4 percent. For stainless steel processed with flux, the average pore area increases to 1.32 square micrometers, the average pore density decreases to 117.5 per millimeter, the average ligament length increases to 6.22 micrometers, and the bonded seam fraction increases to 72.6 percent. The data in FIG. 6B demonstrates that flux addition can improve bonding quality in stainless steel by reducing pore density, increasing average ligament length, and increasing bonded seam fraction.

[0091] The increase in average pore area from 0.22 square micrometers to 1.32 square micrometers in stainless steel samples processed with flux can be attributed to the pore rounding phenomenon. As mentioned above, the pores in stainless steel samples processed without flux can have elongated, thin shapes with sharp comers, which can result in a lower nominal pore area measurement. The pores in stainless steel samples processed with flux can have more spherical shapes with smooth edges, which can result in a higher nominal pore area measurement despite the pores being more stable and resistant to cracking. That is, despite the spherical pores having a larger cross-sectional area, they are more resistant to cracking than elongated pores with sharp comers, and therefore the increase in cross-sectional area is not a detriment to the techniques of the present disclosures.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0092] The reduction in average pore density from 301.6 per millimeter to 117.5 per millimeter in stainless steel samples processed with flux indicates that fewer pores are present along the bonded interface when flux is used. The reduction in pore density can result in a more continuous bond between the stainless steel sheets. The increase in average ligament length from 2.27 micrometers to 6.22 micrometers indicates that the bonded regions between adjacent pores are larger when flux is used during the bonding process, which can improve the overall strength of the bond. The increase in bonded seam fraction from 68.4 percent to 72.6 percent indicates that a greater proportion of the interface is in direct metal-to-metal contact when flux is used.

[0093] The quantitative data presented in FIGS. 6A-6B demonstrates that the flux-assisted solid state bonding process can produce a consolidated metal sheet 120a, 120b having improved bond quality compared to metal sheets bonded without flux. The flux-assisted solid state bonding process can enable production of consolidated metal sheets from oxidized scrap metal, including mild steel and stainless steel, with bond quality suitable for subsequent forming and manufacturing operations. In particular, the improvements in bond quality can result in improved mechanical performance of the consolidated metal sheet, including increased resistance to crack initiation and propagation during mechanical loading. It will be appreciated that while these figures are discussed with respect to mild steel and stainless steel in the figures above, the improvements in the properties discussed above can be seen in other metals and alloys, such as those discussed below.

[0094] FLUX COMPOSITION

[0095] The flux used in the flux-assisted solid state bonding process can include various flux compositions that operate at different temperature ranges. The selection of flux composition can be based on the processing temperature, the alloy composition of the metal sheets being bonded, and the characteristics of the oxide layers to be dissolved. Different flux compositions can have different melting temperatures, viscosity characteristics, and oxide dissolution capabilities, which can affect the performance of the flux during the bonding process.

[0096] The flux can be borax, which operates at an approximate temperature range of about 700°C to about 1250°C. Borax can be selected due to low toxicity and cost, making borax suitable for large-scale industrial applications. Borax can dissolve various oxides, includingAttorney Docket No.: MIT 26265 USPCT | 88212-432500Fe-based, Ni-based, Cr-based, Ti-based, and Mn-based oxides, which can be present on the surfaces of steel, stainless steel, and titanium scrap metal. The approximate temperature range of about 700°C to about 1250°C at which borax melts and becomes reactive can provide flexibility in selecting processing temperatures for different alloy compositions and bonding requirements.

[0097] Various other examples of fluxes can be used. In some embodiments, the flux can be anhydrous sodium metaborate, which can also operate at a temperature approximately in a range of about 700°C to about 1250°C, with the term "operates" being used throughout this disclosure to refer to a temperature range in which the flux can melt and become reactive to oxides of the plurality of materials 104 for the purposes of this disclosure. Anhydrous sodium metaborate can provide oxide dissolution capabilities similar to borax and can be used as an alternative flux composition or in combination with other flux materials. The approximate temperature range of about 700°C to about 1250°C for anhydrous sodium metaborate can overlap with the temperature range for borax, allowing anhydrous sodium metaborate to be used in similar processing conditions as those discussed with respect to borax above.

[0098] The flux can be boric acid, which operates at an approximate temperature range of about 700°C to about 1250°C. Boric acid can provide oxide dissolution capabilities and can be used independently or in combination with other flux materials. The approximate temperature range of about 700°C to about 1250°C for boric acid can be similar to the temperature range for borax, allowing boric acid to be used in similar processing conditions as those discussed with respect to borax above.

[0099] Flux compositions that operate in alternative temperature ranges can be used as well. For example, the flux can be silica, which operates at a temperature range of as those discussed with respect to borax above. Silica can be used as a flux component to modify the viscosity and oxide dissolution characteristics of a flux mixture. The approximate temperature range of about 800°C to about 1250°C for silica can be suitable for processing at elevated temperatures where lower-temperature fluxes may not be effective.

[0100] The flux can be sodium silicate, which operates at an approximate temperature range of about 850°C to about 1300°C. Sodium silicate can provide oxide dissolution capabilities at elevated temperatures and can be used for processing alloys that use higherAttorney Docket No.: MIT 26265 USPCT | 88212-432500bonding temperatures. The approximate temperature range of about 850°C to about 1300°C for sodium silicate can extend the upper temperature limit compared to borax and boric acid, allowing sodium silicate to be used in higher-temperature processing conditions.

[0101] The flux can be sodium fluoride, which operates at an approximate temperature range of about 800°C to about 1200°C. Sodium fluoride can provide oxide dissolution capabilities and can be used independently or in combination with other flux materials. The approximate temperature range of about 800°C to about 1200°C for sodium fluoride can be suitable for processing at elevated temperatures.

[0102] The flux can be potassium fluoride, which operates at an approximate temperature range of about 800°C to about 1200°C. Potassium fluoride can provide oxide dissolution capabilities similar to sodium fluoride and can be used as an alternative flux composition or in combination with other flux materials. The approximate temperature range of about 800°C to about 1200°C for potassium fluoride can overlap with the temperature range for sodium fluoride, allowing potassium fluoride to be used in similar processing conditions.

[0103] The flux can be calcium fluoride, which operates at an approximate temperature range of about 1000°C to about 1400°C. Calcium fluoride can provide oxide dissolution capabilities at elevated temperatures and can be used for processing alloys that use higher bonding temperatures. The approximate temperature range of about 1000°C to about 1400°C for calcium fluoride can extend the upper temperature limit compared to other flux compositions, allowing calcium fluoride to be used in high-temperature processing conditions where other fluxes may not be effective.

[0104] The flux can be sodium chloride, which operates at an approximate temperature range of about 800°C to about 1200°C. Sodium chloride can provide oxide dissolution capabilities and can be used independently or in combination with other flux materials. The approximate temperature range of about 800°C to about 1200°C for sodium chloride can be suitable for processing at elevated temperatures.

[0105] In some embodiments, the flux can be potassium chloride, which operates at an approximate temperature range of about 800°C to about 1200°C. Potassium chloride can provide oxide dissolution capabilities similar to sodium chloride and can be used as an alternative flux composition or in combination with other flux materials. The approximate temperature range of about 800 to about 1200°C for potassium chloride can overlap with theAttorney Docket No.: MIT 26265 USPCT | 88212-432500temperature range for sodium chloride, allowing potassium chloride to be used in similar processing conditions.

[0106] The flux can be ammonium chloride, which operates at an approximate temperature range of about 300°C to about 700°C. Ammonium chloride can provide oxide dissolution capabilities at lower temperatures compared to other flux compositions. The approximate temperature range of about 300°C to about 700°C for ammonium chloride can be suitable for processing at lower temperatures where higher-temperature fluxes may not be appropriate or where lower processing temperatures are desired to reduce energy consumption or to accommodate temperature-sensitive alloy compositions.

[0107] Multiple fluxes can be used together in varying proportions to improve oxide removal, viscosity, and active temperature range. Combining different flux compositions can allow the flux mixture to be tailored for specific processing conditions and alloy compositions. The proportions of different flux components in a flux mixture can be adjusted to achieve desired oxide dissolution characteristics, viscosity behavior, and active temperature range for a particular bonding application. The use of multiple fluxes in combination can extend the effective temperature range of the flux mixture beyond the temperature range of any single flux component, thereby providing greater flexibility in selecting processing temperatures.

[0108] The flux compositions can react chemically with the alloy being bonded and can exchange elements with the alloy through surface reactions. The flux composition can be selected to prevent the evolution of unintended microstructures at the bonded interface. For example, when bonding austenitic stainless steel, the flux composition can be selected to prevent martensite formation at the bonded interface, which could adversely affect the mechanical properties of the consolidated metal sheet. The selection of flux composition based on the alloy composition of the metal sheets being bonded can allow the flux-assisted solid state bonding process to be applied to a wide range of alloy compositions while maintaining desired microstructural characteristics at the bonded interface.

[0109] In some embodiments, roll-bonding can occur at a temperature of at least about 400 degrees Celsius to about 750 degrees Celsius, at least about 400 degrees Celsius to about 500 degrees Celsius, or at a temperature of about 750 degrees Celsius. The processing temperature can be selected based on the flux composition and the alloy composition of theAttorney Docket No.: MIT 26265 USPCT | 88212-432500metal sheets being bonded. Processing temperatures of at least about 750 degrees Celsius can be suitable for use with flux compositions such as anhydrous sodium metaborate, silica, sodium silicate, sodium fluoride, potassium fluoride, calcium fluoride, sodium chloride, and potassium chloride, which have lower temperature limits at or above about 750 degrees Celsius. Processing temperatures of at least about 750 degrees Celsius can also be suitable for use with borax and boric acid, which have lower temperature limits of about 700 degrees Celsius. The selection of processing temperature can be based on the flux composition, the alloy composition, and the desired bonding characteristics for a particular application.

[0110] The flux composition can be selected based on the alloy composition of the metal sheets being bonded to prevent the evolution of unintended microstructures at the bonded interface. Fluxes can react chemically with the alloy being bonded and can exchange elements with the alloy through surface reactions that occur during the flux-assisted solid state bonding process. The exchange of elements between the flux and the alloy can affect the microstructure that develops at the bonded interface during and after the bonding process. Selection of an appropriate flux composition for a particular alloy composition can prevent the formation of undesirable phases or microstructures at the bonded interface that could adversely affect the mechanical properties of the consolidated metal sheet.

[0111] For example, when bonding austenitic stainless steel, the flux composition can be selected to prevent martensite formation at the bonded interface. Austenitic stainless steels can be susceptible to martensite formation when subjected to certain thermal and chemical conditions. Martensite formation at the bonded interface of austenitic stainless steel can adversely affect the mechanical properties and corrosion resistance of the consolidated metal sheet. The flux composition can be selected to avoid chemical interactions that would promote martensite formation, thereby maintaining the austenitic microstructure at the bonded interface and preserving the desired properties of the austenitic stainless steel.

[0112] The flux can dissolve various types of oxides that form on the surfaces of metal sheets, including Al-based, Cu-based, Ti-based, Fe-based oxides, Ni-based oxides, Cr-based oxides, and Mn-based oxides. Al-based oxides can form on the surfaces of aluminum-containing alloys. Cu-based oxides can form on the surfaces of copper-containing alloys. Ti-based oxides can form on the surfaces of copper-containing alloys. Fe-based oxides can form on the surfaces of carbon steels and low-alloy steels, including rust that forms on oxidized or rusted steel scrap. Ni-based oxides can form on the surfaces of nickel-containing alloys,Attorney Docket No.: MIT 26265 USPCT | 88212-432500including stainless steels and nickel-based superalloys. Cr-based oxides can form on the surfaces of chromium-containing alloys, including stainless steels that rely on chromium oxide layers for corrosion resistance. Mn-based oxides can form on the surfaces of manganese-containing alloys, including various steel compositions that contain manganese as an alloying element.

[0113] The ability of the flux to dissolve Al-based, Cu-based, Ti-based, Fe-based, Ni-based, Cr-based, and Mn-based oxides can enable the flux-assisted solid state bonding process to be applied to a wide range of alloy compositions. The flux-assisted solid state bonding process can be applied to any Fe-dominant alloy, including carbon steels, low-alloy steels, and stainless steels that have iron as the primary constituent element. The flux-assisted solid state bonding process can be applied to any Al-dominant alloy, including alloys that have aluminum as the primary constituent element. The flux-assisted solid state bonding process can be applied to any Cu-dominant alloy, including alloys that have copper as the primary constituent element. The flux-assisted solid state bonding process can be applied to any Ti-dominant alloy, including alloys that have titanium as the primary constituent element. The flux-assisted solid state bonding process can also be applied to any Ni-dominant alloy, including nickel-based superalloys and other nickel-based alloys that have nickel as the primary constituent element. The flux-assisted solid state bonding process can be applied to any high entropy alloy. The applicability of the flux-assisted solid state bonding process to Fe-dominant, Al-dominant, Cu-dominant, and Ni-dominant alloys can enable recycling and consolidation of a wide range of scrap metal compositions through the flux-assisted process.

[0114] The flux-assisted solid state bonding process can enable creation of novel composites by bonding different alloy classes that would otherwise be difficult to join through conventional solid state bonding techniques. For example, in some embodiments, a composition of a first material can be different from a composition of a second material in the method of bonding a plurality of materials. The flux-assisted solid state bonding process can enable bonding of dissimilar metals having different alloy or metal compositions by dissolving the oxide layers present on the surfaces of both materials. The ability to bond dissimilar metals can enable creation of metal composites through the flux-assisted rollbonding process, where different alloy compositions are joined to produce a consolidated metal sheet having properties derived from both constituent materials. The flux compositionAttorney Docket No.: MIT 26265 USPCT | 88212-432500can be selected to be compatible with both alloy compositions being bonded, such that the flux can dissolve the oxide layers present on both materials without causing undesirable microstructural changes at the bonded interface of either material.

[0115] For example, the process can bond stainless steel to mild steel, creating a composite having the corrosion resistance of stainless steel on one surface and the lower cost of mild steel in the core. The process can also bond titanium to stainless steel, creating a composite suitable for applications that use the properties of both materials, such as hydrogen barrier applications where a multilayer structure can provide enhanced performance compared to a single-material structure.

[0116] The flux composition can be selected to be compatible with both alloy compositions being bonded in dissimilar metal bonding applications. The flux can dissolve the oxide layers present on both materials without causing undesirable microstructural changes at the bonded interface of either material. The selection of flux composition for dissimilar metal bonding can account for the different oxide compositions that form on the surfaces of the different alloy classes being bonded. For example, when bonding stainless steel to mild steel, the flux can dissolve both the chromium-rich oxide layer on the stainless steel surface and the iron oxide layer on the mild steel surface.

[0117] The flux can be used to introduce new microstructures at the bonded interface during the flux-assisted solid state bonding process. The flux can react chemically with the alloy surfaces during elevated temperature processing, and the chemical reactions between the flux and the alloy surfaces can influence the microstructure that develops at the bonded interface. The flux composition can be selected to promote formation of desired microstructural features at the bonded interface, such as particular phases, grain structures, or compositional gradients that can enhance the properties of the consolidated metal sheet.

[0118] The introduction of new microstructures at the bonded interface through flux-assisted bonding can enable tailoring of interface properties for specific applications. The chemical interactions between the flux and the alloy surfaces can result in local compositional changes at the interface that can promote formation of particular phases or microstructural features. The flux composition and processing parameters can be selected to control the microstructural development at the bonded interface, thereby enabling productionAttorney Docket No.: MIT 26265 USPCT | 88212-432500of consolidated metal sheets having interface properties tailored for specific performance parameters.

[0119] The exchange of elements between the flux and the alloy through surface reactions can occur during the elevated temperature processing of the flux-assisted solid state bonding process. At elevated temperatures, the flux can become molten and can interact chemically with the surfaces of the metal sheets being bonded. The chemical interaction between the molten flux and the metal surfaces can result in exchange of elements across the flux -metal interface. The element exchange can affect the local composition of the metal surfaces and can influence the microstructure that develops at the bonded interface during cooling after the bonding process.

[0120] The selection of flux composition based on the alloy composition of the metal sheets being bonded can account for the element exchange that occurs during the bonding process. Different flux compositions can have different tendencies to exchange particular elements with particular alloy compositions. The flux composition can be selected to minimize undesirable element exchange that could lead to formation of unintended microstructures at the bonded interface. The flux composition can also be selected to promote beneficial element exchange that could improve the properties of the bonded interface or the consolidated metal sheet.

[0121] The method of bonding a plurality of materials can include adjusting one or more of an amount of flux added to the at least one of the first material or the second material, or a location along the surface of the at least one of the first material or the second material to which the flux is added. The adjustment of flux amount and location can be based on various process parameters to achieve effective oxide dissolution and slag expulsion during rollbonding. The process parameters can be optimized to ensure that sufficient flux is present to dissolve all oxide on the surface while avoiding excess flux that could generate excessive slag, each of which can remain trapped at the bonded interface.

[0122] The flux surface density can depend on the flux composition selected for a particular bonding application. Different flux compositions can have different oxide dissolution capabilities and different viscosity characteristics, which can affect the amount of flux being used to achieve effective oxide dissolution and slag expulsion. For borax, the flux surface density can be approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2forAttorney Docket No.: MIT 26265 USPCT | 88212-432500borax. The flux surface density can represent the amount of flux deposited per unit area of the metal sheet surface. A flux surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2can provide sufficient flux to dissolve the oxide layers present on the surfaces of the metal sheets while avoiding excessive flux that could result in slag inclusions at the bonded interface when, for example, roller-induced deformation is not sufficient to extrude the slag. The flux surface density can be adjusted based on the thickness of the oxide layer present on the metal sheet surfaces, with thicker oxide layers using higher flux surface densities to achieve complete oxide dissolution. The flux surface density can be selected based on the oxide thickness, the flux composition, and the deformation parameters to achieve effective oxide dissolution and slag expulsion. Too little flux can result in incomplete oxide dissolution, leaving oxide barriers at the interface that prevent metal-to-metal contact and reduce bond quality, while too much flux can result in excessive slag formation that cannot be fully extruded during roll-bonding, leading to slag inclusions trapped at the bonded interface. It will be appreciated that other flux compositions may use different flux surface density ranges based on the oxide dissolution characteristics and viscosity behavior of the particular flux composition.

[0123] The metal sheets can have a thickness approximately in a range of about 0.1 mm to about 2.7 mm in laboratory scale applications. The thickness approximately in a range of about 0.1 mm to about 2.7 mm can be suitable for laboratory-scale experiments and proof-of-principle testing of the flux-assisted solid state bonding process. Metal sheets within the approximate thickness range of about 0.1 mm to about 2.7 mm can be processed using laboratory-scale rolling equipment to demonstrate the effectiveness of the flux-assisted bonding process.

[0124] In some embodiments, the metal sheets can have a thickness of up to about 20 mm or more in industrial scale applications. The ability to bond thicker metal sheets at industrial scale can depend on having larger rollers that can impart more force on the constituent pieces. Larger rollers can provide greater compressive force during roll-bonding, which can enable effective bonding and slag expulsion for thicker metal sheets. The flux-assisted solid state bonding process can be scaled from laboratory-scale applications of metal sheets with thicknesses approximately in a range of about 0.1 mm to about 2.7 mm to industrial-scale applications using metal sheets with thicknesses in a range of about 20 mm or more by using appropriately sized rolling equipment.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0125] The deformation percentage during rolling can be approximately in a range of about 25% to about 80% thickness reduction. The deformation percentage represents the amount of thickness reduction imparted on the scrap stack during roll-bonding. The deformation percentage can directly affect the ability of the slag to be extruded from the bonded interface. Too little deformation can result in slag inclusions and poor bond quality because insufficient driving force is available to push the slag toward the edges of the consolidated sheet, while too much deformation can limit the geometry of the final slab that is created by excessively reducing the thickness of the consolidated metal sheet.

[0126] A deformation percentage within the approximate range of about 25% to about 80% thickness reduction can provide sufficient driving force to extrude the slag from the bonded interface while maintaining acceptable final sheet geometry. The deformation percentage can be selected based on the flux composition, the processing temperature, and the desired final sheet thickness. Higher deformation percentages can provide greater driving force for slag expulsion but can result in thinner final sheet products. Lower deformation percentages can preserve greater final sheet thickness but may use adjustment of other process parameters, such as rolling speed or processing temperature, to achieve effective slag expulsion.

[0127] The process can enable bonding of metals with variable scrap geometry including different thickness and form factors. The flux-assisted solid state bonding process can accommodate scrap metal pieces having different thicknesses and form factors within a single scrap stack. The variability in scrap geometry can be accommodated by adjusting the flux amount and distribution to ensure thorough coverage of the oxide layers on all scrap metal pieces regardless of individual piece geometry. The ability to bond metals with variable scrap geometry can enable recycling of mixed scrap streams without the need to sort scrap metal pieces by thickness or form factor prior to bonding.

[0128] The adjustment of process parameters based on sheet geometry can account for the variability in scrap metal geometry that can be encountered in recycling applications. The flux surface density, deformation percentage, and rolling speed can be adjusted based on the thickness, form factor, aspect ratio, and size distribution of the scrap metal pieces being bonded. The adjustment of process parameters can ensure effective oxide dissolution and slag expulsion across the entire bonded interface regardless of variations in scrap metal geometry. The ability to adjust process parameters based on sheet geometry can enable theAttorney Docket No.: MIT 26265 USPCT | 88212-432500flux-assisted solid state bonding process to be applied to a wide range of scrap metal compositions and geometries encountered in recycling and manufacturing operations.

[0129] The process can accommodate scrap metal pieces having different cross-sectional geometries within a single consolidated product. Unlike conventional joining processes that can use constituent pieces to have matching cross-sections, the flux-assisted solid state bonding process can bond scrap metal pieces having different cross-sectional shapes and sizes. The deformation imparted during roll-bonding can consolidate the scrap metal pieces into a unified cross-section regardless of the initial cross-sectional geometries of the individual scrap metal pieces. The ability to bond scrap metal pieces having different cross-sectional geometries can increase the flexibility of the recycling process and can enable utilization of scrap metal streams that would otherwise be difficult to consolidate.

[0130] The flux distribution can be adjusted based on the geometry of the scrap metal pieces being bonded to ensure effective oxide dissolution across all surfaces. For scrap metal pieces having irregular geometries, the flux can be applied to ensure coverage of all oxidebearing surfaces that will form bonded interfaces during roll-bonding. The flux surface density can be adjusted based on the surface area and oxide thickness of the scrap metal pieces to ensure sufficient flux is present to dissolve all oxide layers while avoiding excessive flux that could result in slag inclusions at the bonded interfaces.

[0131] The method of bonding a plurality of materials can include collecting the slag from the at least one of the first material A or the second material B after the slag has been expelled during roll-bonding. The expelled slag can be collected from the edges of the consolidated metal sheet where the slag is extraded during the rolling process. The collection of the expelled slag can enable its recycling and reuse as flux, which can reduce material costs and support a more sustainable bonding process.

[0132] The method can include reintroducing flux from the collected slag to the surface of the at least one of the first material A or the second material B. The collected slag can be processed to separate the flux material from the dissolved oxides, and the separated flux can be reapplied to the surfaces of metal sheets for subsequent bonding operations. The ability to reintroduce the flux to the surfaces of metal sheets can enable a continuous recycling loop where flux material is used, collected, processed, and reused in the flux-assisted solid state bonding process.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0133] The method can include dissolving the collected slag in a liquid to separate the flux from oxides bonded thereto. The flux can be water soluble while the oxides are not water soluble, which can allow separation of the flux from the oxides by dissolving the flux in water. For example, when the collected slag is placed in water, the flux can dissolve into the water while the oxides remain as insoluble particles. The insoluble oxide particles can fall out of solution and settle, leaving a flux solution remaining in the water, which can be reused. The separation of flux from oxides based on differential water solubility can provide a straightforward method for recovering flux material from the expelled slag.

[0134] The collected slag can be recycled through a process that includes grinding the slag, soaking the ground flux in water, heating the water, and reapplying the recovered flux to sheet surfaces. The grinding step can break up the collected slag into smaller particles that can more readily dissolve in water. The soaking step can allow the water-soluble flux to dissolve into the water while the insoluble oxides remain as solid particles. The heating step can increase the solubility of the flux in water and can accelerate the dissolution process. After the flux has dissolved and the oxides have settled out of solution, the flux solution can be separated from the oxide particles and can be reapplied to the surfaces of metal sheets for subsequent bonding operations.

[0135] The flux recycling process of the flux-assisted solid state bonding method can provide advantages over conventional molten stage flux or slag recycling. In conventional flux applications involving molten metal, the flux reacts with oxides and impurities to form slag that floats on the surface of the molten metal. The slag formed in conventional molten metal processes can be a dirty flux that is mixed with various chemicals and impurities, which can complicate recyclability of the slag material. The separation of flux from impurities in conventional slag can be difficult due to the complex chemical composition of the slag and the manner in which the flux and impurities are intermixed during the molten metal process.

[0136] The slag expelled during the flux-assisted solid state bonding process of the present disclosure can be more readily recycled compared to conventional molten stage flux or slag. The slag in the solid state bonding process can be expelled from between the metal sheets during roll-bonding, which can result in the slag being collected in a more controlled manner compared to slag that forms on the surface of molten metal. The expelled slag can be collected from the edges of the consolidated metal sheet where the slag is extruded duringAttorney Docket No.: MIT 26265 USPCT | 88212-432500rolling, which can facilitate collection of the slag for recycling. The water solubility of the slag can enable straightforward separation of the flux from the dissolved oxides by dissolving the slag in water to separate out the flux, which can be simpler than separating flux from impurities in conventional slag.

[0137] The recyclability of the flux in the flux-assisted solid state bonding process can support a circular economy approach to metal recycling and consolidation. The ability to collect, process, and reuse the flux material can reduce the amount of flux consumed in the bonding process and can reduce waste generated by the process. The recycling of flux can reduce material costs associated with the flux-assisted solid state bonding process by enabling reuse of flux material that would otherwise be discarded. The flux recycling process can be integrated into the flux-assisted solid state bonding process as part of a continuous operation where flux is applied, expelled during bonding, collected, processed, and reapplied in a continuous cycle.

[0138] The flux-assisted solid state bonding process can be performed as a batch process or a continuous process. In a batch process, a discrete sample can be assembled by depositing flux onto the surfaces of metal sheets, aligning the metal sheets with respect to one another, enclosing the assembled metal sheets within an envelope, preheating the assembled sample, and passing the assembled sample through rollers to achieve bonding. The batch process can provide controlled processing of individual samples, which can be suitable for laboratoryscale experiments, proof-of-principle testing, and applications where precise control over individual sample processing is desired.

[0139] In a continuous process, flux can be sprayed on as the stack is being built while being squeezed out as the stack passes through the rollers. The continuous process can involve feeding metal sheets into a rolling apparatus while simultaneously applying flux to the surfaces of the metal sheets as the metal sheets are assembled into a stack. The flux can be deposited onto the surfaces of the metal sheets using a spray application system that applies a saturated flux solution to the metal sheet surfaces as the metal sheets are fed into the rolling apparatus. The metal sheets with flux deposited thereon can be aligned with respect to one another and fed between an opposed pair of rollers that deform the metal sheets and promote bonding at the interfaces between adjacent metal sheets.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0140] During the continuous process, the slag can be expelled from between the metal sheets as the stack passes through the rollers. The compressive force applied by the rollers can deform the metal sheets and drive the slag toward the edges of the consolidated sheet. The simultaneous application of flux and roll-bonding in the continuous process can enable efficient production of consolidated metal sheets without separate batch processing of individual samples, as mentioned above.

[0141] The continuous process can enable production of metal strips of extended length. The metal sheets can be fed continuously into the rolling apparatus, with flux being applied and bonding occurring as the metal sheets pass through the rollers. The continuous feeding of metal sheets and continuous roll-bonding can produce a consolidated metal strip that extends in length as additional metal sheets are fed into the process. The length of the consolidated metal strip produced through the continuous process can be limited by the supply of metal sheets fed into the rolling apparatus rather than by the processing capacity of individual batch operations.

[0142] The continuous process can add thickness through layer-upon-layerbonding. Additional metal sheets can be fed into the rolling apparatus and bonded onto previously consolidated layers to increase the thickness of the consolidated metal product. The layer-upon-layer bonding approach can enable production of consolidated metal products having thicknesses greater than the thickness of individual metal sheets by successively bonding additional layers onto the consolidated product. The continuous process can enable production of consolidated metal products having both extended length and increased thickness through the combination of continuous feeding and layer-upon-layer bonding.

[0143] The method of bonding a plurality of materials can include finishing a solid state consolidated metal sheet. Finishing the solid state consolidated metal sheet can include trimming edges of the consolidated metal sheet where flux and slag have been expelled during roll-bonding. The trimming operation can remove material from the edges of the consolidated metal sheet that contains expelled slag, flux, and / or remaining oxide residue, thereby producing a consolidated metal sheet having clean edges suitable for subsequent processing or use. Finishing the solid state consolidated metal sheet can also include surface treatment operations, dimensional adjustments, heat treatment operations, or other processingAttorney Docket No.: MIT 26265 USPCT | 88212-432500steps that prepare the consolidated metal sheet for subsequent forming, manufacturing, or end-use applications.

[0144] The continuous process can integrate flux recycling operations with the bonding process. The slag expelled from the edges of the consolidated metal sheet during rollbonding can be collected as the consolidated metal sheet exits the rolling apparatus. The collected slag can be processed to separate the flux material from the dissolved oxides and can be reintroduced into the flux application system for deposition onto subsequent metal sheets fed into the rolling apparatus. The integration of flux recycling with the continuous bonding process can enable a closed-loop operation where flux material is continuously applied, expelled, collected, processed, and reapplied without interruption of the bonding process.

[0145] The flux can facilitate diffusional bonding between the metal sheets by removing oxide barriers and enabling direct metal-to-metal contact at elevated temperatures. At elevated processing temperatures, atomic diffusion can occur across the interface between adjacent metal sheets, promoting metallurgical bonding between the materials. The removal of oxide layers by the flux can enable the diffusional bonding process to proceed without interference from oxide barriers that would otherwise prevent atomic diffusion across the interface. The flux can aid in diffusional bonding by maintaining clean metal surfaces at the interface during the elevated temperature processing.

[0146] A system for consolidating sheet metal according to the present disclosure can include a consolidation portion configured to produce a product from a plurality of sheet metals. The consolidation portion, or consolidator, which can combine a plurality of metals of the same material or different materials, can receive sheet metal pieces and process the sheet metal pieces to form a consolidated metal product through the flux-assisted solid state bonding process described herein. The consolidation portion can be configured to accommodate sheet metal pieces having various thicknesses, form factors, and alloy compositions, and can produce consolidated metal products having properties suitable for subsequent forming, manufacturing, or end-use applications.

[0147] The system for consolidating sheet metal can include a scrap metal adding portion configured to add scrap metal into a receiving cavity of the consolidation portion. The scrap metal adding portion, which can be an opening or a receptacle that holds scrap metal therein,Attorney Docket No.: MIT 26265 USPCT | 88212-432500can feed scrap metal pieces into the consolidation portion for processing through the flux-assisted solid state bonding process. The scrap metal adding portion can be configured to handle scrap metal pieces having variable geometries, including different thicknesses, form factors, and cross-sectional shapes. The scrap metal adding portion can feed scrap metal pieces continuously into the consolidation portion for continuous processing, or can feed discrete batches of scrap metal pieces for batch processing, depending on the configuration of the system and the parameters of a particular application.

[0148] The system for consolidating sheet metal can include a flux adding portion configured to apply a flux to a surface of the plurality of sheet metals. The flux adding portion or receptacle for containing and expelling flux therefrom, can deposit flux onto the surfaces of the sheet metal pieces as the sheet metal pieces are fed into the consolidation portion or as the sheet metal pieces are assembled into a stack for processing. The flux adding portion can apply flux using various deposition methods, including spraying a saturated flux solution onto the sheet metal surfaces, depositing flux granules onto the sheet metal surfaces, or other flux application methods suitable for achieving even distribution of flux across the sheet metal surfaces.

[0149] The flux adding portion can be configured to apply flux at a controlled surface density based on the oxide thickness, alloy composition, and processing parameters for a particular bonding application. The flux adding portion can adjust the amount of flux deposited onto the sheet metal surfaces to achieve a flux surface density within a range suitable for effective oxide dissolution and slag expulsion during roll-bonding. The flux adding portion can apply flux to one or both surfaces of the sheet metal pieces depending on the configuration of the scrap stack and the locations of oxide layers to be dissolved during the bonding process.

[0150] The system for consolidating sheet metal can include a roll bonding portion configured to roll bond the plurality of metal sheets using a plurality of rollers. The roll bonding portion, or rollers, can include an opposed pair of rollers configured to receive the assembled sheet metal pieces and apply compressive force to deform the sheet metal pieces with respect to one another. The rollers can apply sufficient compressive force to promote bonding at the interfaces between adjacent sheet metal pieces while simultaneously driving the slag toward the edges of the consolidated sheet for expulsion.Attorney Docket No.: MIT 26265 USPCT | 88212-432500

[0151] The roll bonding portion can be configured to operate at processing temperatures suitable for flux activation and solid state bonding of the sheet metal pieces. The roll bonding portion can include heating elements or can receive preheated sheet metal assemblies from a preheating station to maintain the sheet metal pieces at elevated temperatures during roll-bonding. The roll bonding portion can operate at rolling speeds selected to provide sufficient time for the viscous slag to be extruded from the bonded interfaces based on the time-dependent flow response of the slag.

[0152] The roll bonding portion can be configured to impart a deformation percentage within a range suitable for effective slag expulsion and bond formation. The rollers 110 of the roll bonding portion can be sized and configured to apply compressive force sufficient to achieve thickness reduction within a range that provides driving force for slag expulsion while maintaining acceptable final sheet geometry. The roll bonding portion can be configured for laboratory-scale processing using smaller rollers or for industrial-scale processing using larger rollers capable of imparting greater compressive force on thicker sheet metal pieces.

[0153] The system for consolidating sheet metal can include a collection portion configured to collect the slag from the surface of the plurality of sheet metals. The collection portion, or storage container or tank, can be positioned to receive slag that is expelled from the edges of the consolidated sheet metal during roll-bonding. The collection portion can collect the expelled flux as the consolidated sheet metal exits the roll bonding portion, enabling recovery of the flux material for recycling and reuse.

[0154] The collection portion can include receptacles, troughs, or other collection structures positioned adjacent to the roll bonding portion to capture the expelled slag. The collection portion can be configured to direct the collected slag to a processing station where the flux can be separated from the dissolved oxides for recycling. The collection portion can enable continuous collection of expelled slag during continuous processing operations, or can collect expelled slag from discrete samples during batch processing operations.

[0155] The system for consolidating sheet metal can integrate the collection portion with a flux recycling system that processes the collected flux for reuse. The flux recycling system can include piping or solutions that separate the flux from the dissolved oxides based on differential water solubility, with the water-soluble flux dissolving in water while theAttorney Docket No.: MIT 26265 USPCT | 88212-432500insoluble oxides remain as solid particles. The separated flux can be returned to the flux adding portion for reapplication to subsequent sheet metal pieces fed into the consolidation portion.

[0156] The system for consolidating sheet metal can be configured for batch processing or continuous processing depending on production parameters and equipment configuration. In a batch processing configuration, the system can process discrete samples of assembled sheet metal pieces through the consolidation portion, with the scrap metal adding portion feeding discrete batches of scrap metal, the flux adding portion applying flux to the assembled batches, and the roll bonding portion processing individual samples. In a continuous processing configuration, the system can continuously feed scrap metal pieces through the scrap metal adding portion, continuously apply flux through the flux adding portion, and continuously roll bond the sheet metal pieces through the roll bonding portion to produce extended length consolidated metal products.

[0157] The system for consolidating sheet metal can include control systems configured to adjust process parameters based on the characteristics of the sheet metal pieces being processed. The control systems can adjust the flux surface density applied by the flux adding portion, the rolling speed of the roll bonding portion, and other process parameters based on the thickness, alloy composition, and oxide characteristics of the sheet metal pieces. The control systems can enable the system to accommodate variable scrap metal streams having different geometries and compositions while maintaining effective oxide dissolution and bond quality.

[0158] The system for consolidating sheet metal can include a preheating portion configured to heat the assembled sheet metal pieces to a processing temperature prior to rollbonding. The preheating portion can include a furnace, induction heating system, or other heating apparatus configured to elevate the temperature of the sheet metal pieces and the flux to a temperature at which the flux becomes active and can dissolve the oxide layers present on the sheet metal surfaces. The preheating portion can be positioned between the flux adding portion and the roll bonding portion in the process flow of the system.

[0159] The system for consolidating sheet metal can include a finishing portion configured to perform finishing operations on the consolidated metal sheet after roll-bonding. The finishing portion can include trimming equipment configured to remove material from theAttorney Docket No.: MIT 26265 USPCT | 88212-432500edges of the consolidated metal sheet where flux and slag have been expelled during rollbonding. The finishing portion can also include surface treatment equipment, dimensional adjustment equipment, or other processing equipment configured to prepare the consolidated metal sheet for subsequent forming, manufacturing, or end-use applications.

[0160] Examples of the above-described embodiments can include the following:1. A method of bonding a plurality of materials, comprising:applying a flux to a surface of at least one of a first material or a second material of a plurality of materials;aligning the plurality of materials with respect to one another such that the flux is disposed between the first material and the second material; androll-bonding the plurality of materials by passing the plurality of materials between an opposed pair of rollers that deform the plurality of materials with respect to one another to form a consolidated metal sheet of the plurality of materials,wherein the flux is applied continuously throughout roll-bonding.2. The method of claim 1, wherein aligning the plurality of materials further comprises placing at least a portion of the first material on top of at least a portion of the second material.3. The method of claim 1 or claim 2, wherein adding the flux and rolling the plurality of materials occurs substantially simultaneously.4. The method of claim 1, wherein the first material and the second material each comprise a metal sheet having a native oxide layer on a surface thereof.5. The method of claim 4, further comprising preheating the plurality of materials prior to rolling the plurality of materials.6. The method of claim 5, wherein the plurality of materials is preheated to a temperature at which the flux dissolves the native oxide layer to form a slag.7. The method of claim 6, further comprising:Attorney Docket No.: MIT 26265 USPCT | 88212-432500expelling the slag from between the first material and the second material to one or more edges of the solid state consolidated metal sheet during roll-bonding;collecting the expelled slag; anddissolving the collected slag in water to separate the flux from oxides,wherein the flux is water soluble and the oxides are not water soluble.8. The method of claim 7, further comprising reapplying the separated flux to a surface of a subsequent metal sheet for a subsequent bonding operation.9. The method of any of claims 4 to 8, wherein the native oxide layer comprises one or more of Fe-based oxides. Al-based oxides, Cu-based oxides, Ni-based oxides, Cr-based oxides, Ti-based, or Mn-based oxides.10. The method of any of claims 1 to 9,wherein the flux comprises borax, andwherein preheating the plurality of materials comprises preheating to a temperature approximately in a range of about 700°C to about 1250°C.11. The method of any of claims 1 to 10, wherein the flux comprises one or more of anhydrous sodium metaborate, boric acid, silica, sodium silicate, sodium fluoride, potassium fluoride, calcium fluoride, sodium chloride, potassium chloride, or ammonium chloride.12. The method of any of claims 1 to 11, wherein the flux is applied as a saturated flux solution that is sprayed onto the surface of the at least one of the first material or the second material to form an even layer of flux upon drying.13. The method of claim 1, wherein the flux is applied at a flux surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2.14. The method of any of claims 1 to 13, wherein a composition of the first material is different from a composition of the second material.15. The method of any of claims 4 to 14, wherein the metal sheets include one or more of rusted steel, stainless steel, or a superalloy.Attorney Docket No.: MIT 26265 USPCT | 88212-43250016. The method of any of claims 5 to 15, wherein the metal sheets include oxidized scrap metal.17. The method of any of claims 1 to 16, wherein the flux is applied without substantial preparation of the surface of the at least one of the first material or the second material.18. The method of any of claims 1 to 17, wherein roll-bonding comprises imparting a thickness reduction approximately in a range of about 25% to about 80% on the plurality of materials.19. The method of any of claims 1 to 18, wherein roll -bonding occurs at a rolling speed approximately in a range of about 1 foot per minute to about 13 feet per minute.20. The method of any of claims 1 to 19, further comprising adjusting one or more of an amount of flux applied to the at least one of the first material or the second material, or a location along the surface of the at least one of the first material or the second material to which the flux is applied based on one or more of sheet geometry, sheet composition, or concentration on the surface.21. The method of claim 20, wherein sheet geometry includes one or more of thickness, form factor, aspect ratio, flux surface density, processing temperature, reduction amount, or size distribution.22. The method of any of claims 1 to 21, further comprising collecting the slag from the at least one of the first material or the second material and reintroducing the flux from the slag to the surface of the at least one of the first material or the second material.23. The method of claim 22, further comprising dissolving the collected slag in a liquid to separate the flux from oxides bonded thereto.24. The method of any of claims 1 to 17, wherein roll -bonding occurs at a temperature of at least about 750 degrees Celsius.25. The method of any of claims 1 to 18, further comprising finishing the solid state consolidated metal sheet.26. A consolidated metal sheet formed by any of the methods of claims 1 to 25.Attorney Docket No.: MIT 26265 USPCT | 88212-43250027. A method of continuously producing a consolidated metal sheet, comprising:feeding a plurality of metal sheets having native oxide layers on surfaces thereof into a rolling apparatus;applying a flux to one or more surfaces of each of the plurality of metal sheets as the plurality of metal sheets are fed into the rolling apparatus, wherein the flux is applied at a surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2;heating the plurality of metal sheets to a temperature of at least about 700°C such that the flux dissolves the native oxide layers to form a slag;passing the plurality of metal sheets between an opposed pair of rollers to deform the plurality of metal sheets and expel the slag from between the plurality of metal sheets; and collecting the expelled slag from edges of the consolidated metal sheet.28. The method of claim 27, wherein the flux comprises borax, and wherein heating the plurality of metal sheets comprises heating to a temperature approximately in a range of about 700°C to about 1250°C.29. The method of claim 27 or claim 28, wherein the plurality of metal sheets comprises one or more of 1000 series mild steel or 300 series stainless steel.30. The method of any of claims 27 to 29, wherein passing the plurality of metal sheets between the opposed pair of rollers comprises imparting a thickness reduction approximately in a range of about 25% on the plurality of sheets to about 80% on the plurality of metal sheets.31. The method of any of claims 27 to 30, further comprising:dissolving the collected slag in water to separate the flux from oxides,wherein the flux is water soluble and the oxides are not water soluble.32. The method of any of claims 27 to 31 , further comprising reapplying the separated flux to surfaces of subsequent metal sheets fed into the rolling apparatus.33. The method of any of claims 27 to 32, wherein applying the flux comprises spraying a saturated flux solution onto the surfaces of the plurality of metal sheets to form an even layer of flux upon drying.Attorney Docket No.: MIT 26265 USPCT | 88212-43250034. The method of any of claims 27 to 33, wherein the plurality of metal sheets has thicknesses approximately ranging from about 0.1 mm to about 20 mm.35. The method of any of claims 27 to 34, wherein the native oxide layers comprise one or more of Fe-based oxides, Ni-based oxides, Cr-based oxides, or Mn-based oxides.36. The method of any of claims 27 to 35, wherein a rolling speed is approximately in a range of about 1 foot / minute to about 8 feet / minute.37. A system for consolidating sheet metal, comprising:a consolidation portion configured to produce a product from a plurality of sheet metals;a scrap metal adding portion configured to add scrap metal into the receiving cavity of the consolidation portion;a flux adding portion configured to apply a flux to a surface of the plurality of sheet metals; anda roll bonding portion configured to roll bond the plurality of metal sheets using a plurality of rollers.38. The system of claim 37, further comprising a collection portion configured to collect slag from the surface of the plurality of sheet metals.39. The system of claim 37 or claim 38, wherein the flux adding portion is configured to spray a saturated flux solution onto the surfaces of the plurality of metal sheets to form an even layer of flux upon drying.40. The system of any of claims 37 to 39, wherein the flux adding portion is configured to apply the flux at a surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2.41. The system of any of claims 37 to 40, wherein the preheating portion is configured to heat the plurality of metal sheets to a temperature approximately in a range of about 700°C to about 1250°C.Attorney Docket No.: MIT 26265 USPCT | 88212-43250042. The system of any of claims 37 to 41, wherein the roll bonding portion is configured to impart a thickness reduction approximately in a range of about 25% on the plurality of metal sheets to about 80% on the plurality of metal sheets at a rolling speed approximately in a range of about 1 foot per minute to about 13 feet per minute.43. The system of any of claims 37 to 42, further comprising a flux recycling portion configured to dissolve the collected slag in water to separate the flux from oxides and to return the separated flux to the flux adding portion for reapplication to subsequent metal sheets.

[0161] One skilled in the art will appreciate further features and advantages of the disclosure based on the above -described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. By way of example, the flux-assisted solid state bonding process can be applied to consolidate scrap metal from various industrial sectors including transportation, construction, machinery, and metal goods manufacturing, and can be adapted for bonding of additional alloy compositions beyond mild steel and stainless steel, such as aluminum, copper, nickel, galvanized steel, titanium, and superalloys. A person skilled in the art, in view of the present disclosures, will be able to adapt some or all of the various systems, devices, and methods disclosed herein for recycling and consolidating metal scraps in continuous or batch manufacturing operations, for creating dissimilar metal composites through flux-assisted roll-bonding, and for integrating flux recycling systems into existing scrap metal consolidation infrastructure. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

Attorney Docket No.: MIT 26265 USPCT | 88212-432500CLAIMS1. A method of bonding a plurality of materials, comprising:applying a flux to a surface of at least one of a first material or a second material of a plurality of materials;aligning the plurality of materials with respect to one another such that the flux is disposed between the first material and the second material; androll-bonding the plurality of materials by passing the plurality of materials between an opposed pair of rollers that deform the plurality of materials with respect to one another to form a consolidated metal sheet of the plurality of materials,wherein the flux is applied continuously throughout roll-bonding.

2. The method of claim 1, wherein adding the flux and rolling the plurality of materials occurs substantially simultaneously.

3. The method of claim 1, wherein the first material and the second material each comprise a metal sheet having a native oxide layer on a surface thereof.

4. The method of claim 3, further comprising preheating the plurality of materials prior to rolling the plurality of materials.

5. The method of claim 4, wherein the plurality of materials is preheated to a temperature at which the flux dissolves the native oxide layer to form a slag.

6. The method of claim 5, further comprising:expelling the slag from between the first material and the second material to one or more edges of the solid state consolidated metal sheet during roll-bonding;collecting the expelled slag; anddissolving the collected slag in water to separate the flux from oxides,wherein the flux is water soluble and the oxides are not water soluble.

7. The method of claim 1,wherein the flux comprises borax, andwherein preheating the plurality of materials comprises preheating to a temperature approximately in a range of about 700°C to about 1250°C.Attorney Docket No.: MIT 26265 USPCT | 88212-4325008. The method of claim 1, wherein the flux is applied as a saturated flux solution that is sprayed onto the surface of the at least one of the first material or the second material to form an even layer of flux upon drying.

9. The method of claim 1, wherein the flux is applied at a flux surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2.

10. The method of claim 1, wherein the flux is applied without substantial preparation of the surface of the at least one of the first material or the second material.

11. The method of claim 1, wherein roll-bonding comprises imparting a thickness reduction approximately in a range of about 25% to about 80% on the plurality of materials.

12. The method of claim 1, further comprising adjusting one or more of an amount of flux applied to the at least one of the first material or the second material, or a location along the surface of the at least one of the first material or the second material to which the flux is applied based on one or more of sheet geometry, sheet composition, or concentration on the surface.

13. The method of claim 12, wherein sheet geometry includes one or more of thickness, form factor, aspect ratio, flux surface density, processing temperature, reduction amount, or size distribution.

14. The method of claim 1, further comprising collecting the slag from the at least one of the first material or the second material and reintroducing the flux from the slag to the surface of the at least one of the first material or the second material.

15. The method of claim 14, further comprising dissolving the collected slag in a liquid to separate the flux from oxides bonded thereto.

16. A method of continuously producing a consolidated metal sheet, comprising:feeding a plurality of metal sheets having native oxide layers on surfaces thereof into a rolling apparatus;Attorney Docket No.: MIT 26265 USPCT | 88212-432500applying a flux to one or more surfaces of each of the plurality of metal sheets as the plurality of metal sheets are fed into the rolling apparatus, wherein the flux is applied at a surface density approximately in a range of about 0.03 g / cm2to about 0.15 g / cm2;heating the plurality of metal sheets to a temperature of at least about 700°C such that the flux dissolves the native oxide layers to form a slag;passing the plurality of metal sheets between an opposed pair of rollers to deform the plurality of metal sheets and expel the slag from between the plurality of metal sheets; and collecting the expelled slag from edges of the consolidated metal sheet.

17. The method of claim 16, further comprising:dissolving the collected slag in water to separate the flux from oxides,wherein the flux is water soluble and the oxides are not water soluble.

18. The method of claim 16, further comprising reapplying the separated flux to surfaces of subsequent metal sheets fed into the rolling apparatus.

19. The method of claim 16, wherein applying the flux comprises spraying a saturated flux solution onto the surfaces of the plurality of metal sheets to form an even layer of flux upon drying.

20. The method of claim 16, wherein a rolling speed is approximately in a range of about 1 foot / minute to about 8 feet / minute.

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