A method for improving intermetallic solid phase deposition additive interface bonding strength

Abstract

This invention belongs to the field of solid-state deposition additive manufacturing technology, specifically relating to a method for improving the interfacial bonding strength between metals in solid-state deposition additive manufacturing. The method includes: providing a shaped metal substrate to be processed; forming a curved path groove on the surface of the shaped metal substrate by machining, the groove having a trapezoidal cross-section that is wider at the top and narrower at the bottom; and depositing metal material layer by layer onto the surface of the machined shaped substrate using solid-state deposition additive manufacturing to the required thickness, thereby obtaining a shaped part. This invention, by machining a curved path groove with a narrower top and wider bottom cross-section on the substrate surface before solid-state deposition additive manufacturing, synergistically enhances the mechanical interlocking capability between the first deposited layer and the substrate, thereby effectively resisting interfacial shear stress and pull-out stress generated by multiple thermal cycles, preventing the first deposited layer from peeling off. It has outstanding advantages such as excellent anti-peeling performance, simple process, low cost, and strong adaptability.

Description

Technical Field

[0001] This invention belongs to the field of solid-phase deposition additive manufacturing technology, and specifically relates to a method for improving the interfacial bonding strength of solid-phase deposition additive manufacturing between metals. Background Technology

[0002] In high-end manufacturing fields such as aerospace, automotive manufacturing, power electronics, and nuclear energy engineering, the performance of a single metal material is often insufficient to meet the comprehensive requirements of lightweight structures, electrical conductivity, thermal conductivity, and corrosion resistance under complex working conditions. Therefore, reliable bonding between dissimilar metals has become a key technical path to achieve multifunctional components. However, the bonding process of dissimilar metals faces three major challenges in physicochemical compatibility: First, the significant differences in thermophysical properties such as melting point, thermal conductivity, and coefficient of linear expansion between dissimilar metals lead to extremely uneven thermal stress distribution and residual stress during heating and cooling, which can easily cause deformation or even cracking at the interface. Second, dissimilar metals have limited mutual solubility in liquid or solid states and are prone to forming brittle intermetallic compounds at the interface. For example, when copper / aluminum, steel / aluminum, steel / copper, titanium / aluminum, nickel / aluminum, or titanium / steel are bonded, if the hard and brittle intermetallic compound layer is too thick, it will promote crack initiation and propagation, significantly deteriorating mechanical properties. Third, significant electrochemical potential differences exist between dissimilar metals, making them highly susceptible to forming macroscopic corrosion galvanes in humid or corrosive environments, leading to electrochemical corrosion failure of the joint. Traditional fusion welding methods are often difficult to apply directly to dissimilar metal connections because high dilution rates and intense metallurgical reactions make it difficult to control the brittle phase. Taking copper / aluminum transition components, widely used in power plant busbar connections, substation outgoing terminals, zinc electrowinning cathode conductive heads, and transformer leads, as an example, the physicochemical properties of copper and aluminum differ significantly: copper has a melting point of 1083℃, while aluminum has a melting point of 660℃, a difference of approximately 400℃; copper's coefficient of thermal expansion is 16.5 × 10⁻⁶. -6 / ℃, aluminum is 23.8×10 -6 The difference in temperature is 1.44 times; the standard electrode potential of copper is +0.34V, while that of aluminum is -1.66V, a potential difference of up to 2.0V. Therefore, how to effectively control the distribution of residual stress, suppress the excessive growth of brittle intermetallic compounds, avoid galvanic corrosion, and achieve high-strength and high-reliability connections at the intermetallic interface has always been a core challenge in this field.

[0003] In recent years, solid-state deposition additive manufacturing technology has been considered a promising new method for metal joining due to its low processing temperature and ability to avoid material melting, thus suppressing the continuous formation of brittle intermetallic compounds. This technology uses the intense plastic deformation of high-speed solid particles or rotating rods to deposit metallic materials layer by layer on the substrate surface, thereby fabricating composite metal parts. However, in actual multilayer deposition processes, it has been found that the first deposited layer is highly susceptible to interfacial delamination from the substrate under repeated thermal cycles during subsequent multilayer depositions. Analysis suggests that the accumulation of thermal stress caused by repeated thermal cycles, the release of residual interfacial stress, and the formation of localized brittle phases collectively weaken the bonding strength between the first deposited layer and the substrate. This first-layer delamination problem severely restricts the reliable application of solid-state deposition additive manufacturing technology in the fabrication of composite metal parts, becoming a key technical bottleneck that urgently needs to be addressed.

[0004] Currently, the main method to improve the intermetallic bonding strength is to introduce one or more intermediate transition materials to alleviate the physicochemical differences between different metals, inhibit the formation of brittle intermetallic compounds, and improve the interfacial bonding strength. Taking copper / aluminum as an example, commonly used intermediate layer materials include silver (Ag), nickel (Ni), zinc (Zn), tin (Sn), and their alloys. The intermediate layer can be applied to the copper substrate surface through electroplating, electroless plating, physical vapor deposition, magnetron sputtering, or pre-placed foil. Its mechanism of action mainly includes: ① acting as a diffusion barrier layer to inhibit the interdiffusion of copper and aluminum atoms; ② buffering interfacial thermal stress through the plastic deformation capacity of the intermediate layer itself; ③ forming a better solid solution or intermetallic compound with copper and aluminum, avoiding the formation of continuous brittle phases. The drawbacks of this method are as follows: First, new brittle phases may still be generated between the intermediate layer material and copper and aluminum, especially under repeated thermal cycling, the risk of interface embrittlement still exists; second, the preparation process of the intermediate layer is complex and costly, and the multi-layer interface increases the risk of failure during long-term service; more importantly, the intermediate layer cannot solve the peeling problem that is prone to occur in the first deposition layer during solid phase deposition additive manufacturing, the interface is still mainly chemically bonded, and the peeling resistance is limited.

[0005] Therefore, there is a lack of existing technologies that can effectively improve the interfacial bonding strength of the first deposition layer in intermetallic solid-phase deposition additive manufacturing. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for improving the interfacial bonding strength of solid-state deposition additive manufacturing between metals. This method involves processing a curved groove with a narrow top and wide bottom cross-section on the substrate surface before solid-state deposition additive manufacturing. This synergistically enhances the mechanical interlocking ability between the first deposited layer and the substrate, effectively resisting interfacial shear stress and pull-out stress generated by multiple thermal cycles, preventing the first deposited layer from peeling off. It has outstanding advantages such as excellent anti-peeling performance, simple process, low cost, and strong adaptability.

[0007] The technical solution of this invention is as follows: A method for improving the interfacial bonding strength of solid-state deposition additive manufacturing between metals includes: providing a shaped metal substrate to be processed; forming a curved path groove on the surface of the shaped metal substrate by machining, the groove having a trapezoidal structure with a wider top and a narrower bottom; and depositing metal material layer by layer on the surface of the machined shaped substrate to the required design thickness by solid-state deposition additive manufacturing to obtain a shaped part.

[0008] In this process, trenches with curved paths are machined into the surface of the copper substrate, creating a periodically varying tortuous path within the plane. This structure provides multi-directional mechanical resistance to the deposited layer in the horizontal direction, preventing the first layer from sliding and peeling off in any direction. The trench cross-section is narrower at the top and wider at the bottom, forming an inverted anchoring effect of "larger inside and smaller outside," which prevents the deposited layer from being pulled out of the trench in the vertical direction, effectively resisting the pull-out stress generated by thermal cycling. Combining the curved planar tortuous path with the narrow-at-the-top, wide-at-the-bottom trench cross-section structure forms a three-dimensional, all-around mechanical anchoring system that simultaneously resists vertical pull-out stress and multi-directional shear stress, avoids stress concentration, and significantly improves the peel resistance of the first layer under repeated thermal cycling.

[0009] Before solid-phase deposition additive manufacturing, the copper substrate surface is prefabricated with curved paths and narrow tops and wide bottoms, creating trenches. This allows the first deposition layer to be partially filled and anchored in the trenches during the deposition process, eliminating the need for intermediate layer materials. This fully utilizes the combined effect of metallurgical bonding and mechanical interlocking, thereby simplifying the process and reducing production costs.

[0010] In some implementation schemes, the machining method is not specifically limited and can be CNC milling, laser machining, or micro electrical discharge machining.

[0011] In some embodiments, the bending path is a curved or zigzag bend. The curved bend is S-shaped or wavy, while the zigzag bend is serrated or Z-shaped. Preferably, the bending path is S-shaped, and the chord lengths of two adjacent circular arcs of the S-shape are equal. More preferably, the chord length is 2-4 mm. Equal chord lengths ensure consistent geometry and curvature variation in each arc segment. When the joint is under load, the equal chord length design provides symmetrical tensile / shear resistance, avoids localized failure, and facilitates manufacturing.

[0012] In some embodiments, the groove is a dovetail groove. Preferably, the width of the dovetail groove opening is 0.4~0.6mm, the width of the groove bottom is 0.8~1.2mm, and the groove depth is 0.4~0.6mm.

[0013] In some implementations, the process includes surface cleaning of the shaped metal substrate before and after machining. Before machining, the shaped metal substrate is surface-cleaned to remove oil, oxide layers, and impurities. Specifically, a polar organic solvent, such as acetone or ethanol, can be used for ultrasonic cleaning for 5-10 minutes, followed by rinsing with deionized water and finally drying in a drying oven at 60-80°C. After machining, the substrate with curved grooves is cleaned again to remove residual chips and oil. This can be achieved using a combination of compressed air purging and ultrasonic cleaning to ensure no residual impurities remain in the grooves. After cleaning, the substrate is dried at low temperature under inert gas protection or directly fed into a solid-phase deposition additive manufacturing system.

[0014] In some embodiments, the shaped metal substrate and the metal material deposited on its surface may be of the same or different material, selected from copper, aluminum, steel, titanium, or nickel. Preferably, the shaped metal substrate and the metal material deposited on its surface are selected from any combination of the following: copper / aluminum, steel / aluminum, steel / copper, titanium / aluminum, nickel / aluminum, and titanium / steel.

[0015] Solid-state deposition additive manufacturing is an additive manufacturing technology that uses mechanical force and frictional heat to soften materials to a plastic state at temperatures below their melting point, and then deposits layers to form a dense three-dimensional structure. It includes friction stir deposition and friction extrusion deposition, with friction stir deposition being the preferred method. More preferably, the raw material for the deposited metal coating is a square-section rod, with the following parameters: the cross-sectional area of ​​the square-section rod is 5~15mm×5~15mm, preferably 8~12mm×8~12mm; the diameter of the tool head is 20~40mm, preferably 26~30mm; the rotational speed of the tool head is 600~2000 rpm, preferably 600~1000 rpm; the travel speed is 20~300 mm / min, preferably 30~200mm / min, more preferably 30~100mm / min; the rod feed rate is 5 mm / min~100 mm / min, preferably 5 mm / min~50 mm / min, more preferably 5 mm / min~20 mm / min; and the thickness of a single layer is 0.5 mm~3mm, preferably 0.5 mm~1.5mm.

[0016] In some implementations, the substrate after the metal material has been deposited is also machined to remove excess material from the edges.

[0017] The beneficial effects of this invention are as follows: 1. The method provided by this invention, in addition to interfacial metallurgical bonding, enhances mechanical interlocking capability and significantly improves peel resistance through three-dimensional omnidirectional mechanical anchoring. Specifically, this invention combines a curved planar tortuous path with a groove cross-section structure that is narrower at the top and wider at the bottom to form a three-dimensional omnidirectional anchoring system: the narrower-at-the-top cross-section generates a reverse buckling effect in the vertical direction, preventing the deposited layer from being pulled out; the curved planar tortuous path generates tortuous resistance against multi-directional shear in the horizontal direction, preventing the deposited layer from slipping. The synergistic effect of these two elements enables the first deposited layer to simultaneously resist vertical pull-out stress and multi-directional shear stress during multiple thermal cycles in the intermetallic solid-phase deposition additive manufacturing process.

[0018] 2. The method provided by this invention can effectively disperse accumulated stress under multiple thermal cycling conditions. Specifically, this invention disperses the interfacial shear stress to multiple bending segments through a tortuous structure with a curved shape, avoiding stress concentration; at the same time, it uses a cross-section that is narrow at the top and wide at the bottom to convert the vertical pull-out stress into the sidewall extrusion stress, so that the interfacial stress accumulated by thermal cycling can be effectively released, solving the technical problem in the prior art that the first deposited layer peels off after several thermal cycles.

[0019] 3. The method provided by this invention is simple, low-cost, and requires no intermediate layer material. Specifically, this invention achieves a significant improvement in peel resistance simply by pre-fabricating trenches on the surface of the copper substrate, without adding any intermediate materials. It is highly compatible with existing solid-phase deposition additive manufacturing processes and is easy to implement for industrial applications. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A top view of an "S"-shaped meandering trench; Figure 2 This is a schematic diagram of the longitudinal section structure of the trench; Wherein: 1-copper substrate; 2-"S" shaped zigzag groove; 3-groove opening; 4-groove bottom; 5-groove sidewall; d-chord length of two adjacent positive and negative circular arcs; h-groove depth; w1-groove opening width; w2-groove bottom width. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 A method for improving the bonding strength of the solid-phase deposition additive interface between copper and aluminum metals, comprising the following steps: (1) Surface pretreatment of copper substrate The surface of the copper substrate to be processed is ultrasonically cleaned with ethanol for 10 minutes, then rinsed with deionized water, and dried in a drying oven at 60°C for later use.

[0024] (2) Machining “S” shaped bends and grooves On the copper substrate surface to be deposited, a meandering groove with an "S" shape is machined using CNC milling. The projection of this groove onto the plane is a continuous "S" shaped curve, where the chord lengths of two adjacent positive and negative circular arcs of the S are equal, d=3 mm.

[0025] The groove has a dovetail groove structure that is narrow at the top and wide at the bottom. The processing parameters of the groove are: groove depth h = 0.5 mm, groove opening width w1 = 0.5 mm, and groove bottom width w2 = 1 mm.

[0026] (3) Post-trenching After processing, the copper substrate with the "S"-shaped grooves is cleaned again to remove residual chips and oil. Compressed air purging combined with ultrasonic cleaning is used to ensure no impurities remain in the grooves. After cleaning, it is dried at low temperature under inert gas protection.

[0027] (4) Solid-phase deposition additive manufacturing of the first deposition layer The pretreated copper substrate is fixed on the worktable of the solid-phase deposition additive manufacturing equipment. Aluminum is deposited on the surface of the copper substrate using solid-phase deposition additive manufacturing technology to form the first deposition layer. The process parameters are set as follows: tool head diameter 28 mm, additive aluminum square rod cross-sectional area 10 mm × 10 mm, tool head rotation speed 800 rpm, feed speed 30 mm / min, aluminum rod feed rate 9 mm / min, and single-layer thickness 1 mm.

[0028] (5) Deposit layer by layer to the target thickness Based on the initial deposition layer, multiple layers are deposited until the designed transition thickness is achieved. During each subsequent deposition process, the initial deposition layer undergoes multiple thermal cycles, but thanks to the anchoring effect of the "S"-shaped tortuous trenches, the initial deposition layer maintains a strong bond with the copper substrate, preventing interface delamination.

[0029] (6) Post-processing After completing all additive deposition, machining is performed to remove excess material from the edges, resulting in a copper / aluminum transition part. The copper / aluminum transition part primarily bears shear loads during service; therefore, the interfacial shear strength was tested, reaching 120 MPa. This indicates that the first layer of aluminum deposition on the copper substrate exhibits excellent anti-peeling performance, thus ensuring the connection reliability and stability of the copper / aluminum transition part during long-term service.

[0030] Example 2 A method for improving the bonding strength of the solid-phase deposition additive interface between titanium and aluminum metals, comprising the following steps: (1) Surface pretreatment of titanium substrate The surface of the titanium substrate to be processed is ultrasonically cleaned with ethanol for 10 minutes, then rinsed with deionized water, and dried in a drying oven at 60°C for later use.

[0031] (2) Machining “S” shaped bends and grooves On the titanium substrate surface to be deposited, a meandering groove with an "S" shape is machined using CNC milling. The projection of this groove onto the plane is a continuous "S" shaped curve, where the chord lengths of two adjacent positive and negative circular arcs of the S are equal, d=3 mm.

[0032] The groove has a dovetail groove structure that is narrow at the top and wide at the bottom. The processing parameters of the groove are: groove depth h = 0.5 mm, groove opening width w1 = 0.5 mm, and groove bottom width w2 = 1 mm.

[0033] (3) Post-trenching After processing, the titanium substrate with the "S"-shaped grooves is cleaned again to remove residual chips and oil. Compressed air purging combined with ultrasonic cleaning is used to ensure no impurities remain in the grooves. After cleaning, it is dried at low temperature under inert gas protection.

[0034] (4) Solid-phase deposition additive manufacturing of the first deposition layer The pretreated titanium substrate is fixed on the worktable of the solid-phase deposition additive manufacturing equipment. Aluminum is deposited on the surface of the titanium substrate using solid-phase deposition additive manufacturing technology to form the first deposition layer. The process parameters are set as follows: tool head diameter 28 mm, additive aluminum square rod cross-sectional area 10 mm × 10 mm, tool head rotation speed 800 rpm, travel speed 30 mm / min, aluminum rod feed rate 9 mm / min, and single layer thickness 1 mm.

[0035] (5) Deposit layer by layer to the target thickness Based on the first deposited layer, multiple layers are deposited until the designed transition thickness is achieved. During each subsequent deposition process, the first deposited layer undergoes multiple thermal cycles, but thanks to the anchoring effect of the "S"-shaped tortuous grooves, the first deposited layer maintains a strong bond with the titanium substrate, and no interfacial delamination occurs.

[0036] (6) Post-processing After completing all additive deposition, machining is performed to remove excess material from the edges, resulting in a titanium / aluminum composite part. The first layer of aluminum deposited on the titanium substrate exhibits excellent peel resistance. During service, the tensile strength along the additive height direction of the titanium / aluminum composite part is of paramount importance, achieving a tested strength of 260 MPa. This ensures the connection reliability and stability of the titanium / aluminum composite part during long-term service.

[0037] Comparative Example 1 The difference from Example 1 is that the groove cross-section has a structure with equal width at the top and bottom. The processing parameters of the groove are: groove depth h = 0.5 mm, groove opening width = groove bottom width = 1 mm. The measured interfacial shear strength is 97 MPa, which is lower than 120 MPa in Example 1.

[0038] Comparative Example 2 The difference from Example 1 is that the groove direction is a straight line. The measured interfacial shear strength is 106 MPa, which is lower than 120 MPa in Example 1.

[0039] Comparative Example 3 The difference from Example 2 is that the groove cross-section has a structure with equal width at the top and bottom. The processing parameters of the groove are: groove depth h = 0.5 mm, groove opening width = groove bottom width = 1 mm. The measured tensile strength is 195 MPa, which is lower than 260 MPa in Example 2.

[0040] Comparative Example 4 The difference from Example 2 is that the groove runs in a straight line. The measured tensile strength was 224 MPa, which is lower than the 260 MPa of Example 2.

[0041] By comparing the results of Example 1 with Comparative Example 1, Example 1 with Comparative Example 2, and Example 2 with Comparative Example 3 and Example 2 with Comparative Example 4, it can be seen that compared with the molded parts prepared by using only a curved shape path or only a trapezoidal structure with a wider top and narrower bottom, the molded parts prepared by using a curved shape path + a trapezoidal structure with a wider top and narrower bottom have significantly improved interface bonding strength and significantly better peel resistance.

[0042] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of improving intermetallic solid phase deposition additive interface bond strength, characterized in that, The method includes: Provide the shaped metal substrate to be processed; Curved path grooves are formed on the surface of the molded metal substrate by mechanical processing, the cross-section of the grooves being a trapezoidal structure wider at the top and narrower at the bottom; and, Solid-phase deposition additive manufacturing involves depositing metal material layer by layer onto the surface of a machined metal substrate to the required thickness, thereby obtaining a shaped part.

2. The method according to claim 1, characterized in that, The curved path is either a curved path or a broken line path. The curved path is S-shaped or wavy, and the broken line path is zigzag or Z-shaped.

3. The method according to claim 2, characterized in that, The curved path is S-shaped, and the chord lengths of two adjacent positive and negative circular arcs of S are equal.

4. The method according to claim 3, characterized in that, The chord length is 2~4mm.

5. The method according to claim 1, characterized in that, The groove is a dovetail groove.

6. The method according to claim 5, characterized in that, The dovetail groove has an opening width of 0.4~0.6mm, a bottom width of 0.8~1.2mm, and a depth of 0.4~0.6mm.

7. The method according to claim 1, characterized in that, It also includes surface cleaning treatment of the formed metal substrate before and after machining.

8. The method according to claim 7, characterized in that, The surface cleaning process includes: rinsing with a polar organic solvent and / or deionized water, purging, and drying.

9. The method according to claim 1, characterized in that, The shaped metal substrate may be the same as or different from the metal material deposited on its surface, and may be selected from copper, aluminum, steel, titanium or nickel.

10. The method according to claim 9, characterized in that, The materials of the shaped metal substrate and the metal material deposited on its surface are respectively referred to as the first metal and the second metal, and are selected from any combination of the following: (1) The first metal is copper, and the second metal is aluminum; (2) The first metal is steel, and the second metal is aluminum; (3) The first metal is steel, and the second metal is copper; (4) The first metal is titanium, and the second metal is aluminum; (5) The first metal is nickel, and the second metal is aluminum; (6) The first metal is titanium and the second metal is steel.

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