A steel-aluminum ash slag pressure brazing composite method

Abstract

The present invention discloses a steel-aluminum ash pressure brazing composite method, which belongs to the field of brazing. The method is as follows: a layer of brazing material is coated on the surface of a die 4 with a stepped hole on the inner wall, and molten aluminum ash 2 is poured into the die 4 through an inclined flow channel 3 with an alumina ceramic coating on the inner surface. After the pouring is completed, the riser is immediately squeezed with a hydraulic press head, and the pressure is maintained, the heat is kept, and the cooling is slowed. The riser and the die sleeve 6 are cut, and the mold steel cover plate 5 is welded, and then T4, T5 or T6 heat treatment is performed. The advantage of the present invention over the existing brazing technology is that the high temperature of the molten aluminum ash 2 is used as a heat source to melt the brazing material, saving external energy. The brazing interface adopts a pressure welding composite connection method, which enhances the bonding strength of the weld joint and reduces residual stress. The forming precision is high, the external toughness of the product is good, the internal hardness is high, the weight is light, and the compressive strength is high. The process is simple, easy to promote, the product has high use value, and solid hazardous waste resource utilization is realized.

Description

[0001] Field

[0002] The invention belongs to the field of brazing, and in particular relates to a steel-aluminum ash slag pressure brazing composite method. Background Art

[0003] Aluminum ash is the scum and skimming residue that floats on top of the molten aluminum during the smelting process of electrolytic aluminum, cast aluminum, and recycled aluminum. It also includes the residue remaining after subsequent processes such as roasting and ball milling. It is considered a hazardous solid waste. The chemical composition of aluminum ash (slag) is primarily composed of metallic aluminum and oxides, with aluminum oxide typically accounting for over 60%. Other oxides include silicon oxide, magnesium oxide, sodium oxide, iron oxide, calcium oxide, and aluminum nitride. A major byproduct of the aluminum industry, aluminum ash is generated in all aluminum melting processes, and its aluminum content accounts for approximately 1-12% of the total aluminum loss during production and use. Discarding aluminum slag as waste not only wastes aluminum resources but also creates environmental problems. Therefore, finding cost-effective methods to utilize and manage aluminum ash slag will not only improve the economic benefits of the aluminum processing industry, but also effectively recycle resources and have a significant impact on achieving sustainable economic and social development. Currently, waste aluminum ash is primarily used to produce aluminum sulfate, aluminum powder, and basic aluminum chloride. These products have low added value and require more advanced processing technologies.

[0004] Brazing is a solid-phase connection. Unlike fusion welding, the base material does not melt during brazing. A brazing material with a lower melting point than the base material is used, and the heating temperature is lower than the solidus line of the base material but higher than the liquidus line of the brazing material. Chinese scholars have studied the buffer layer mechanism of Si3N4 / 40Cr steel brazed joints. Pressure brazing is used to promote plastic deformation of the buffer layer, reduce the residual stress of the joint, and improve the strength of the joint. Patent CN103084690A discloses a method for ultra-high pressure brazing connection of tungsten-diamond / copper-low activation steel. Patent CN101693326A discloses a silver-free copper-based brazing material used for high-frequency induction pressure brazing to complete large-area composite brazing of stainless iron / copper / stainless steel dissimilar metals in one go. The weld shear strength τ b ≥100Mpa. Currently, there are no reports on the research and application of pressure brazing composite of aluminum ash slag and steel. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a steel-aluminum ash slag pressure brazing composite method. The composite material manufactured by this method has good mechanical properties, low cost, high product added value, realizes solid waste resource utilization, and is conducive to promotion and application.

[0006] The technical solution of the present invention is: Figure 1As shown, the inner surface of the steel die 4 (also the outer shell of the workpiece) is coated with a layer of brazing material. After preheating, it is fixed to a vibrating table on the hydraulic press workbench and begins to vibrate up and down. The molten aluminum slag 2 in the crucible 1 is poured into the die 4 through a long U-shaped inclined flow channel 3 with an outer steel inner surface coated with an alumina coating. The inner wall of the die 4 has stepped holes with axes perpendicular to the die plane (the so-called stepped holes are multiple large blind holes with a diameter of 30mm opened at intervals of 30mm on the inner wall surface, and then a small through hole with a diameter of 2mm is opened in the center of the bottom of each large blind hole). The high temperature of the molten aluminum slag 2 is used to melt the brazing material, achieving steel-aluminum slag brazing. The molten aluminum slag 2's easy flow characteristics and vibration force are utilized to make the aluminum slag liquid fill the die 4 under the action of the vibration force and exhaust through the small holes in the stepped holes of the die. After the casting is completed, when the workpiece is in a thixotropic state, the hydraulic press head is immediately used to squeeze the riser. The pressure is transmitted to the brazing interface to promote the formation of the interface buffer layer. Plastic deformation is generated, which reduces the residual stress of the joint and improves the connection strength of the joint. The molten aluminum ash slag crystallizes and solidifies under pressure and forcibly eliminates shrinkage cavities and shrinkage caused by solidification shrinkage. After maintaining the pressure for a certain period of time, the pressure head is lifted and covered with insulation material. After cooling to room temperature, the die sleeve 6 is separated, the riser is cut off, and the mold steel cover plate 5 (which is also the workpiece steel cover plate) is covered. The steel cover plate 5 is welded and sealed to the side wall of the die 4 to obtain a steel-aluminum ash slag pressure brazing composite part with a steel shell, a brazing material in the middle interface layer, and an aluminum ash slag casting without casting defects inside. Finally, the formed part is subjected to T4 heat treatment, T5 heat treatment or T6 heat treatment.

[0007] The process flow is as follows: coating brazing material on the inner surface of the mold 4, preheating the mold 4, smelting and slag removal, vibrating the mold 4, rheological casting using the inclined flow trough 3, closing the mold and applying pressure, maintaining pressure, removing the punch, keeping warm, cutting the die sleeve 6 and the riser, welding the steel cover plate 5, heat treatment, and product.

[0008] Technical Parameters

[0009] In the steel-aluminum ash slag pressure brazing composite forming process, the main process parameters involved are: brazing flux, mold preheating temperature, aluminum ash slag liquid pouring temperature, pressurization start time, thixotropic extrusion pressure ratio, holding time, workpiece cooling, heat treatment, etc. The specific process parameters are as follows:

[0010] Brazing flux: eutectic flux of potassium tetrafluoroaluminate and potassium hexafluoroaluminate.

[0011] Mold preheating temperature: Preferably, the mold preheating temperature is 300-350°C.

[0012] Aluminum ash slag pouring temperature: Determine the ideal aluminum ash slag pouring temperature based on the liquidus temperature and solidification range of the aluminum ash slag, and control it at the lowest value. For aluminum ash slag with smaller heat capacity, it is preferably 80°C above the aluminum ash slag liquidus, otherwise it is 50°C above the aluminum ash slag liquidus.

[0013] Solid fraction: Preferably, the solid content of the aluminum ash slurry flowing into the mold is controlled to be 40-60% by adjusting the length and angle of the inclined flow channel.

[0014] Pressurization start time: Preferably, pressurization is applied immediately after the aluminum ash slag liquid fills the metal mold cavity.

[0015] Thixotropic extrusion pressure ratio: preferably, the pressure ratio value is 140-190 MPa.

[0016] Holding time: The length of the holding time mainly depends on the maximum wall thickness of the workpiece section and is calculated and selected based on the cooling rate of 0.5-1mm / Sec.

[0017] Cooling: After thixotropic extrusion is released, the punch is removed immediately (the die is not removed). To prevent cracks during air cooling due to the high temperature of the workpiece, the die and the workpiece are immediately buried with sand or soil and removed for air cooling after cooling to room temperature.

[0018] The advantages of the present invention are:

[0019] 1. The high temperature of molten aluminum ash is used as the heat source to melt the brazing material, saving external energy.

[0020] 2. The brazing interface adopts pressure welding composite connection method, which enhances the bonding strength of the joint and reduces residual stress.

[0021] The present invention also has the following beneficial effects: aluminum ash slag is an industrial solid waste, and my country's annual output is huge. Inventing a comprehensive utilization technology with low cost and high added value is beneficial to the country and the people. Rheocasting plus thixotropic extrusion densification is an emerging process combining casting and forging. It has the advantages of simple casting process, low raw material cost, and complex parts shape, and also has the characteristics of fine grains, uniform structure, good mechanical properties, and high forming precision of die forging products. The main advantages are as follows: (1) The molten aluminum ash slag flows into the die through an inclined long steel trough. During the flow process, the slurry forms a semi-solid structure. (2) During the thixotropic forming process, the aluminum ash slag liquid that has not yet solidified is crystallized and solidified under the action of isostatic pressing from beginning to end, and flows into shape; the solidified aluminum ash slag layer undergoes plastic deformation under pressure, has a thermal deformation structure, fine grains, and uniform structure. (3) Under the action of pressure, the solid-liquid zone undergoes forced shrinkage compensation, thereby eliminating defects such as shrinkage cavities and looseness inside the part, and improving the mechanical properties of the part. (4) The fluidity of aluminum ash slag liquid during rheocasting is much greater than that of solid aluminum ash slag, and its performance in filling the mold is better. It can form parts with relatively complex shapes in one mold. (5) The density and mechanical properties are basically equivalent to those of aluminum ash slag die forgings. (6) The high-temperature aluminum ash slag scraped out during aluminum smelting is poured into the die forging mold through an inclined flow trough for pressure forming, without the need for secondary heating, which saves labor and energy. (7) After rheocasting, the molten aluminum ash slag is formed and solidified under pressure, so that the part and the cavity wall fit tightly. The air gap between the molds is reduced, which increases the thermal conductivity and accelerates the solidification speed, which is conducive to grain refinement. In addition, the workpiece after rheocasting and pressurization has a higher surface finish and dimensional accuracy, and its level can reach the level of die casting. Therefore, aluminum ash slag rheocasting is an important method for near-net forming. (8) Rheocasting is carried out on a hydraulic press. It is easy to achieve mechanization and automation, greatly reduces the labor intensity of people, and improves the production environment of the workshop. (9) During the solidification process, the rheological casting is pressurized, and all parts are under compressive stress, which is beneficial to the shrinkage compensation of the parts and the prevention of cracks in the parts. Therefore, the practicality of this process is relatively strong and is not limited by the casting performance of aluminum ash slag. (10) The outer shell of the part is made of steel with good toughness, and the interior is made of rheological casting thixotropic extrusion densification with high cohesive strength, light weight, high hardness, wear resistance, high temperature resistance, corrosion resistance, and impact resistance without casting defects. After this deep processing of solid waste resources, the added value of aluminum ash slag is increased. The product can be used as wear-resistant, corrosion-resistant, and impact-resistant parts, and is widely used in metallurgy, mining, chemical industry, and electricity. It can also be used as bulletproof armor modules and applied in the field of military engineering protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0023] Figure 1 Schematic diagram of the inclined flow channel rheocasting process

[0024] Figure 2 Schematic diagram of the side view of the workpiece

[0025] Figure 3 Schematic diagram of the cross-section of the workpiece

[0026] Figure 4 Schematic diagram of the die sleeve 6

[0027] Figure 5 Schematic diagram of steel cover

[0028] Reference numerals:

[0029] 1- Crucible 2- Molten aluminum ash 3- Diagonal chute 4- Die 4.1- Die side steel plate 4.2- Die bottom steel plate 5- Steel cover 6- Die sleeve DETAILED DESCRIPTION

[0030] The exemplary embodiments of the present invention will be described in more detail below in conjunction with the accompanying drawings in accordance with the embodiments of the present invention. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0031] The part's overall dimensions are 400x400x80mm. The die is welded from 30mm thick 616 armor steel. The die consists of a lower die 4 and a die sleeve 6, both welded from steel plates. Before welding, blind holes with a diameter of 30mm and a depth of 10mm are drilled every 30mm on the inner surface of the lower die 4. A 2mm through-hole is drilled in the center of each blind hole. The die sleeve 6 is welded from 30mm thick 616 armor steel, with the same length, width, and shape as the lower die, but with a height of 30mm. The difference is that it lacks a bottom. When in use, it fits over the lower die 4 and is spot welded to the lower die 4 on its outer surface. The die sleeve 6 serves as a guide for the ram and compensates for the aluminum slag inside the die sleeve.

[0032] After pouring the aluminum ash slag liquid 2, a 5000KN three-beam four-column hydraulic press is used for pressurization. After pouring, a thixotropic extrusion densification composite process is performed: the steel die 4 with stepped holes is fixed on the vibration table of the hydraulic press workbench. The outward-convex half-mold (male mold) serves as the punch for metal stamping and is fixed to the movable crossbar of a hydraulic press. A eutectic brazing paste of potassium tetrafluoroaluminate and potassium hexafluoroaluminate is applied to the inner surface of the mold (4). The mold is preheated, and molten aluminum slag liquid (3) is poured into the female mold (4) through an inclined trough (3). The vibrating table vibrates up and down. After the vibration ends, the male mold is pressed vertically downward, and the aluminum slag liquid (3) in the female mold is pressed by the male mold machine to fill the mold cavity. It solidifies under pressure and forms a steel-aluminum slag brazing composite. The high temperature of the molten aluminum slag (3) melts the brazing material, achieving a steel-aluminum slag brazing composite. The extrusion force transmitted to the brazing interface causes plastic deformation of the interface buffer layer, reducing residual stress in the joint and improving joint strength. The molten aluminum slag crystallizes and solidifies under pressure, forcibly eliminating shrinkage cavities and porosity caused by solidification shrinkage. After a period of pressure maintenance, the male mold is lifted. At this point, the female mold (4) and the aluminum slag block become one. After lifting the pressure head, immediately bury it in sand to cool slowly. When it cools to room temperature, take it out, cut off the die sleeve 6 and the riser, weld on the steel cover plate 5, and the workpiece is formed and manufactured. Finally, heat treatment is carried out. The specific process parameters are as follows: Mold 4 preheating temperature: 350℃. Casting temperature: 80℃ higher than the liquidus temperature of the aluminum ash 3. Solid fraction: By adjusting the length and angle of the inclined flow channel 3, the solid phase content of the aluminum ash slurry flowing into the mold 4 is controlled at 40-60%. The interval for starting pressurization after pouring: Start pressurization immediately after pouring. Specific pressure value: 290Mpa. The downward movement speed of the punch during extrusion: 30mm / s. Holding time: 5 minutes.

[0033] Quantitative pouring of aluminum ash slag liquid: The volumetric method is used to quantify the amount of aluminum ash slag liquid poured into the concave mold. When designing the mold concave mold sleeve 6, an opening can be opened in the upper part of the mold sleeve 6 to allow excess aluminum ash slag to flow out during rheocasting, acting as an overflow device and ensuring that the casting dimensions are not deviated due to excessive pouring of aluminum ash slag.

[0034] Workpiece Cooling: After rheocasting pressure is released, the punch is immediately lifted. Because the demolding temperature of the workpiece is high, in order to prevent cracks from forming during air cooling of the high-temperature workpiece, the demolded workpiece is immediately buried in sand and removed for air cooling after cooling to room temperature.

[0035] The formed parts are subjected to T4 heat treatment: (solution treatment (400-490°C, 8-10h) + quenching + natural aging; the formed parts are subjected to T5 heat treatment (150-200°C, 8-12h) or T6 heat treatment (solution treatment (400-490°C, 8-10h) + quenching + artificial aging (120-160°C, 24-48h)).

[0036] The above are only preferred embodiments of the invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the conceptual principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A steel-aluminum ash slag pressure brazing composite method, characterized in that: The following steps are involved: (1) uniformly coating a layer of brazing material on the inner surface of the steel die (4); (2) preheating the die (4) to a set temperature and fixing it on a vibration table on a hydraulic press workbench; (3) starting the vibration table to vibrate the die (4) up and down; (4) pouring the molten aluminum ash (2) in the crucible (1) into the die (4) through an inclined U-shaped chute (3), wherein the outer surface of the chute (3) is made of steel and the inner surface is coated with an aluminum oxide coating; (5) utilizing the high temperature of the molten aluminum ash (2) to melt the brazing material, thereby achieving steel-aluminum ash brazing composite; simultaneously, utilizing the fluidity and vibration of the molten aluminum ash (2) to fill the die (4) with the aluminum ash liquid, and exhausting the gas through the stepped holes on the inner wall of the die (4); the axis of the stepped holes being perpendicular to the plane of the die (4); (6) After the casting is completed, when the workpiece is in a thixotropic state, the riser is immediately squeezed with a hydraulic press head; the pressure is transmitted to the brazing interface to cause the interface buffer layer to produce plastic deformation, reduce the residual stress of the joint, and improve the joint strength; at the same time, the molten aluminum ash slag (2) crystallizes and solidifies under pressure, forcibly eliminating the shrinkage cavities and porosity formed by solidification shrinkage; (7) After holding the pressure for the set time, lift the pressure head and cover the workpiece with insulation material; (8) After cooling to room temperature, the steel cover plate (5) is welded and sealed to the side steel plate (4.1) of the die (4) to obtain a steel-aluminum ash pressure brazing composite part with a steel shell, a steel-aluminum ash interface layer as brazing material, and an aluminum ash casting inside; (9) The composite part is subjected to T4 heat treatment, T5 heat treatment or T6 heat treatment.

2. The steel-aluminum ash slag pressure brazing composite method according to claim 1, characterized in that: The mold used in steps (1) and (2) consists of two parts, a die (4) and a die sleeve (6), both of which are welded with steel plates; before welding, the stepped holes are machined on all inner surfaces of the die (4); the die sleeve (6) has a size and shape that matches the die (4), and when in use, it is sleeved on the die (4), and its outer surface is fixed to the die (4) by spot welding.

3. The steel-aluminum ash slag pressure brazing composite method according to claim 1 or 2, characterized in that: The preheating temperature in step (2) is 300-350°C; the pouring temperature of the molten aluminum ash (2) in step (4) is 50-80°C above the liquidus line of the aluminum ash; the specific pressure value of the extrusion in step (6) is 140-190 MPa; the holding time in step (7) is calculated and determined based on the maximum wall thickness of the cross-section of the workpiece at a cooling rate of 0.5-1 mm / sec; after cooling to room temperature in step (8), the die sleeve (6) and the riser are cut off, and then the steel cover plate (5) is welded; the stepped hole spacing is 20-30 mm, and is composed of a blind hole with a diameter of 20-30 mm and a through hole with a diameter of 2 mm located at the center of its bottom.

4. The steel-aluminum ash slag pressure brazing composite method according to claim 3, characterized in that: The stepped holes have a spacing of 30 mm and are composed of a blind hole with a diameter of 30 mm and a depth of 10 mm and a through hole with a diameter of 2 mm located at the center of the bottom thereof.

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