A low stress diffusion bonding method suitable for copper / titanium dissimilar materials

Abstract

The application relates to a low-stress diffusion connection method suitable for copper / titanium dissimilar materials, and aims to solve the problem of low connection strength caused by excessive interface residual stress of the existing copper / titanium dissimilar alloy diffusion connection joint. The diffusion connection method comprises the following steps: one, filling the particle material for adjusting the thermal expansion coefficient in the groove or array circular groove of the copper workpiece, and filling the zirconium oxide particles in the groove or array circular groove of the titanium workpiece; two, using a friction stir head to respectively perform friction stir surface treatment on the welding surfaces of the copper workpiece and the titanium workpiece; three, oppositely connecting the welding surfaces of the copper workpiece and the titanium workpiece, and performing vacuum diffusion connection at a temperature of 600-900 DEG C. The application introduces the silicon carbide particles on the surface of the copper alloy plate through the friction stir surface treatment process, introduces the zirconium oxide ceramic particles on the surface of the titanium alloy plate, adjusts the CTE of the friction stir treatment areas of the copper alloy and the titanium alloy respectively, and reduces the interface residual stress of the dissimilar material joint.

Description

Technical Field

[0001] The invention belongs to the field of metal material connection, and in particular relates to a diffusion connection method for copper / titanium dissimilar materials. Background Art

[0002] Titanium alloys, with their high specific strength and corrosion resistance, have become indispensable materials in manufacturing industries such as aerospace and biomedicine. Copper alloys, on the other hand, possess excellent electrical and thermal conductivity and are widely used in power engineering, the electronics industry, and heat exchange systems. In certain applications, it is essential to leverage the unique properties of both materials to achieve a reliable connection. In addition to mechanical assembly and gluing, welding methods, such as solid-phase diffusion bonding, can also be used to create copper / titanium dissimilar joints.

[0003] However, due to the large difference in thermal expansion coefficients between copper alloy and titanium alloy materials—the thermal expansion coefficient (CTE) of copper alloy is 17.2×10 -6 ·K -1 , while the CTE of titanium alloy is 8.5×10 -6 ·K -1 Direct diffusion joints of dissimilar materials often suffer from high residual stress, resulting in poor joint plasticity and low joint strength. Therefore, it is of great significance to develop a method that can regulate the CTE of the copper / titanium dissimilar diffusion interface to achieve low-stress, high-strength joining. Summary of the Invention

[0004] The present invention aims to solve the problems of excessive interface residual stress in existing copper / titanium dissimilar alloy diffusion bonding joints and the resulting poor joint plasticity and low connection strength, and provides a low-stress diffusion bonding method suitable for copper / titanium dissimilar materials.

[0005] The low stress diffusion bonding method suitable for copper / titanium dissimilar materials of the present invention is implemented by the following steps:

[0006] Step 1: Processing multiple grooves or arrays of circular grooves on the surfaces to be welded of the copper workpiece and the titanium workpiece, respectively. Then, the copper workpiece and the titanium workpiece are cleaned and dried. The grooves or arrays of circular grooves of the copper workpiece are filled with granular materials for adjusting the thermal expansion coefficient, and the grooves or arrays of circular grooves of the titanium workpiece are filled with zirconium oxide (ZrO2) particles.

[0007] Step 2: using a friction stir head to perform friction stir surface treatment on the to-be-welded surfaces of the copper workpiece and the titanium workpiece, respectively, to obtain pretreated copper workpieces and titanium workpieces;

[0008] Step 3: Grind and polish the pre-treated copper and titanium workpiece surfaces to be welded, place the copper and titanium workpiece surfaces to be welded opposite each other, apply joining pressure, and perform vacuum diffusion bonding in a vacuum diffusion furnace at a temperature of 600-900°C, thereby completing low-stress diffusion bonding between the copper and titanium dissimilar materials.

[0009] The material of the granular material for adjusting the thermal expansion coefficient in step 1 is silicon carbide, titanium carbide, tungsten carbide, molybdenum powder, tungsten powder, zirconium tungstate or yttrium tungstate.

[0010] The surface with a different CTE from the original base material is obtained by pre-grooved filling particles combined with friction stir surface treatment, that is, for the copper alloy plate with a higher CTE (CTE = 17.2 × 10 -6 ·K -1 ), by introducing a material with extremely low CTE such as silicon carbide (CTE = 4.7 × 10 -6 ·K -1 ) powder, tungsten powder (CTE = 4.5 × 10 -6 ·K -1 ) or molybdenum powder (CTE = 4.8 × 10 -6 ·K -1 ) and negative thermal expansion coefficient materials such as zirconium tungstate (CTE = -8.7 × 10 -6 ·K -1 ) and so on, significantly reducing the CTE of the copper alloy surface material; while for the titanium alloy plate on the side with lower CTE (CTE = 8.5 × 10 -6 ·K -1 ), by introducing zirconium oxide with a CTE higher than that of titanium alloy (CTE = 10.2×10 -6 ·K -1 ) particles, which improves the CTE of the titanium alloy surface to a certain extent. After the CTE difference between the interface of the copper alloy and the titanium alloy treated by the stir friction surface CTE adjustment treatment is effectively reduced, the residual stress of the diffusion bonding interface is reduced. In addition, in addition to the CTE adjustment effect on the surface of the plate during the stir friction surface treatment, the treatment process is accompanied by the coupling behavior of frictional heat generation and shear flow of the plasticized metal material. After the original coarse grains in the alloy plate structure are broken, incomplete dynamic recrystallization occurs, forming a fine-grained structure with more dislocation defects. These changes are conducive to reducing the diffusion activation energy of the interface in subsequent diffusion bonding and improving the diffusion coefficient. Since the residual stress is reduced and the diffusion metallurgical bonding is more sufficient, the plasticity and connection strength of the joint are effectively improved. The present invention can realize low-stress diffusion bonding between copper / titanium dissimilar materials, and has good technical application effects and broad application prospects.

[0011] The low-stress diffusion bonding method for copper / titanium dissimilar materials of the present invention has the following beneficial effects:

[0012] 1. The present invention increases the coefficient of thermal expansion (CTE) of the titanium alloy side while reducing the CTE of the copper alloy side, thereby achieving a more matched combination of the diffusion welding interface between the two, thereby reducing the residual stress at the diffusion welding interface of the copper / titanium dissimilar materials and improving the joint plasticity and connection strength;

[0013] 2. The friction stir treated surface of the copper / titanium dissimilar materials in the present invention has the microstructural characteristics of fine grains and multiple dislocations, the diffusion bonding interface has a lower diffusion activation energy and a higher diffusion coefficient, the metallurgical diffusion is more sufficient, and the joint bonding is reliable;

[0014] 3. The present invention realizes direct diffusion connection of copper / titanium dissimilar material interfaces without changing the properties of the parent materials and without adding an intermediate layer. It has little impact on the functionality of materials outside the joint interface and has wide technical adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the process of filling CTE adjusting particles in the prefabricated grooves according to the present invention;

[0016] Figure 2 Schematic diagram of the friction stir surface treatment process of the present invention;

[0017] Figure 3 Schematic diagram of the low stress diffusion bonding process of the present invention;

[0018] Figure 4 The CTE curves of the copper and titanium plates after adding CTE adjusting particles in Example 1 and the CTE comparison diagram of each treated surface at 200°C are shown;

[0019] Figure 5 This is a backscattered electron microscopy photograph of the copper-titanium diffusion interface obtained after interface CTE adjustment in Example 1;

[0020] Figure 6 Schematic diagram of the low-stress diffusion bonding method suitable for copper / titanium dissimilar materials according to the present invention. DETAILED DESCRIPTION

[0021] Specific embodiment 1: This embodiment is suitable for the low stress diffusion bonding method between copper and titanium dissimilar materials and is implemented according to the following steps:

[0022] Step 1: Processing multiple grooves or arrays of circular grooves on the surfaces to be welded of the copper workpiece and the titanium workpiece, respectively. Then, the copper workpiece and the titanium workpiece are cleaned and dried. The grooves or arrays of circular grooves of the copper workpiece are filled with granular materials for adjusting the thermal expansion coefficient, and the grooves or arrays of circular grooves of the titanium workpiece are filled with zirconium oxide (ZrO2) particles.

[0023] Step 2: using a friction stir head to perform friction stir surface treatment on the to-be-welded surfaces of the copper workpiece and the titanium workpiece, respectively, to obtain pretreated copper workpieces and titanium workpieces;

[0024] Step 3: Grind and polish the pre-treated copper and titanium workpiece surfaces to be welded, place the copper and titanium workpiece surfaces to be welded opposite each other, apply joining pressure, and perform vacuum diffusion bonding in a vacuum diffusion furnace at a temperature of 600-900°C, thereby completing low-stress diffusion bonding between the copper and titanium dissimilar materials.

[0025] The material of the granular material for adjusting the thermal expansion coefficient in step 1 is silicon carbide, titanium carbide, tungsten carbide, molybdenum powder, tungsten powder, zirconium tungstate or yttrium tungstate.

[0026] This embodiment addresses the problem of excessive residual stress in the connection caused by the large difference in the coefficient of thermal expansion (CTE) in the diffusion bonding of copper / titanium dissimilar materials. By introducing silicon carbide (SiC) particles with a lower CTE on the surface of the copper alloy plate through a stir friction surface treatment process, and introducing zirconium oxide (ZrO2) ceramic particles with a higher CTE on the surface of the titanium alloy plate, respectively, the CTE of the stir friction treatment area on the copper alloy surface is lowered and the CTE of the titanium alloy surface treatment area is increased, thereby alleviating the CTE difference between the two materials and reducing the interfacial residual stress of the dissimilar material joint. In addition, in addition to filling the plate surface with CTE adjustment particles during the stir friction surface treatment, the treatment process is accompanied by the coupling behavior of frictional heat generation and shear flow of the plasticized metal material. After the original coarse grains in the alloy plate structure are broken, incomplete dynamic recrystallization occurs, forming a fine-grained structure with more dislocation defects, which is beneficial to reducing the diffusion activation energy of the interface in the subsequent diffusion bonding and improving the diffusion coefficient. Due to the reduction of residual stress and more complete diffusion metallurgical bonding, the plasticity and connection strength of the joint are effectively improved.

[0027] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the material of the copper workpiece in step 1 is pure copper, brass, aluminum bronze or white copper.

[0028] Specific embodiment three: The difference between this embodiment and specific embodiment one or two is that the material of the titanium workpiece in step one is pure titanium (TA1, TA2), TC4 alloy, TC6 alloy, TC11 alloy or TB6 alloy.

[0029] Specific embodiment 4: This embodiment differs from any one of specific embodiments 1 to 3 in that the particle size of the granular material for adjusting the thermal expansion coefficient and the zirconium oxide particles in step 1 is 0.01 to 10 μm.

[0030] Specific embodiment 5: The difference between this embodiment and specific embodiments 1 to 4 is that the width of the groove in step 1 is 0.5-1.5 mm, and the depth of the groove is 0.1-0.3 mm; the diameter of the array circular groove is 0.5-4 mm, and the depth of the circular groove is 0.1-0.3 mm.

[0031] Specific embodiment six: The difference between this embodiment and specific embodiments one to five is that in the stir friction surface treatment process in step two, the stir friction head speed is controlled to be 220-380rpm, the travel speed is 20-100mm / min, the inclination angle is 0-3.5°, and the piercing treatment depth is 0.1-0.8mm.

[0032] The friction stirring head in this embodiment is in the form of a needle-free flat shoulder, a needle-free shoulder with an indented angle, or a stirring head with a stirring needle.

[0033] Specific embodiment seven: This embodiment differs from any one of specific embodiments one to six in that in step three, the pre-treated copper workpiece and the titanium workpiece to be welded are mechanically ground and polished respectively.

[0034] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that the connection pressure applied in step three is 2 to 30 MPa.

[0035] Specific embodiment 9: The difference between this embodiment and any one of specific embodiments 1 to 8 is that the time for vacuum diffusion connection in step 3 is 5 to 100 minutes.

[0036] Specific embodiment ten: This embodiment differs from specific embodiments one to nine in that in step three, vacuum diffusion bonding is performed at a temperature of 700 to 900° C. for 20 to 50 minutes.

[0037] Example 1: This example is suitable for a low-stress diffusion bonding method between copper and titanium dissimilar materials. The method is implemented by the following steps:

[0038] Step 1: Process the following shapes on the welded surfaces of the C11000 copper alloy sheet and the TC4 titanium alloy sheet: Figure 1 The grooves shown have a depth of 0.18 mm and a width of 1.5 mm. The C11000 copper alloy sheet and the TC4 titanium alloy sheet are then cleaned and dried. The grooves of the C11000 copper alloy sheet are filled with silicon carbide powder having an average particle size of 5 μm, and the grooves of the TC4 titanium alloy sheet are filled with zirconium oxide (ZrO2) particles having an average particle size of 8 μm.

[0039] Step 2: Use a needle-free flat shoulder friction stir head to perform friction stir surface treatment on the copper workpiece and the titanium workpiece to be welded (such as Figure 2 As shown), the friction stir processing parameters are controlled as follows: rotation speed of 400 rpm, travel speed of 50 mm / min, inclination angle of 0.5°, and shoulder plunging depth of 0.2 mm to obtain pretreated copper and titanium workpieces;

[0040] Step 3: Grind and polish the pre-treated copper workpiece and titanium workpiece surfaces to be welded, place the copper workpiece and titanium workpiece surfaces to be welded together, and apply a connection pressure of 8 MPa. Figure 3 As shown, vacuum diffusion bonding is performed in a vacuum diffusion furnace at a temperature of 730° C. for 40 minutes, thereby completing low-stress diffusion bonding between copper and titanium dissimilar materials.

[0041] In this embodiment, the CTE of copper and titanium plates changes after adding CTE regulating particles. The CTE curves at different temperatures are measured by thermal expansion instrument as shown in the following figure: Figure 4 As shown in a, the CTE comparison of each treated surface at 200℃ is obtained. Figure 4 As shown in Figure b, it can be seen that after the surface friction stir treatment and filling with silicon carbide particles, the CTE of the copper plate surface is reduced to a certain extent; while the CTE of the titanium alloy surface is slightly improved after filling with zirconium oxide particles and undergoing friction stir treatment. The CTE difference of the copper / titanium interface measured by the thermal expansion instrument at 200°C steady-state conditions after the friction stir surface CTE adjustment is 12.1×10 -6 ·K -1 Reduced to 9.2×10 -6 ·K -1 In this embodiment, the copper-titanium diffusion interface obtained after adjusting the interface CTE is as follows: Figure 5 As shown in the figure, the interface microstructure shows that the positive and negative CTE adjustment particles are dispersed near the titanium and copper interfaces. After the CTE difference between the materials on both sides of the interface is reduced, the interface residual stress generated by the thermal shrinkage and deformation inconsistency of the copper / titanium dissimilar materials during the diffusion cooling stage can be effectively alleviated (schematic diagram as shown in the figure). Figure 6 This helps improve joint plasticity and connection strength. Experimental measurements show that the joint shear strength achieved under the process conditions of this example is 93 MPa, a 20.7% increase compared to the direct diffusion joint strength of 77 MPa achieved under the same process conditions in the untreated control group.

[0042] Example 2: This example differs from Example 1 in that in step 1, an array of circular grooves is machined on the surfaces to be welded of the B10 cupronickel alloy sheet and the TB6 titanium alloy sheet, respectively. The depth of the circular grooves is 0.2 mm, the diameter of the circular grooves is 1.5 mm, and the spacing between the circular grooves is 2 mm. Then, the B10 cupronickel alloy sheet and the TB6 titanium alloy sheet are cleaned and dried, and the circular grooves of the B10 cupronickel alloy sheet are filled with a 4.5×10-6 ·K -1 Tungsten carbide particles with an average particle size of 0.5 μm are used, and zirconium oxide (ZrO2) particles with an average particle size of 3 μm are filled in the circular grooves of the TB6 titanium alloy plate workpiece;

[0043] The experimental results show that the joint shear strength obtained under the process conditions of this embodiment is 103 MPa, which is 21.2% higher than the direct diffusion joint strength of 85 MPa obtained under the same process conditions without treatment on the copper side of the control group.

[0044] In summary, compared to the large CTE difference on both sides of the interface in existing copper / titanium direct diffusion processes, by filling CTE-adjusting particles and performing surface stir friction treatment, the CTE on the copper alloy side of the diffusion bonding interface is lowered and the CTE on the titanium alloy side is increased, thereby reducing the degree of material shrinkage and deformation caused by diffusion cooling, thereby reducing the residual stress at the copper / titanium diffusion bonding interface and improving the plasticity and strength of the joint. Because the surface treatment process is also accompanied by the coupled behavior of frictional heat generation and shear flow of the plasticized metal material, the original coarse grains in the alloy plate structure are broken and incomplete dynamic recrystallization occurs, forming a fine-grained structure with more dislocation defects. These changes help reduce the diffusion activation energy of the interface in subsequent diffusion bonding and increase the diffusion coefficient, thereby achieving a more complete metallurgical bond at the interface and a stronger joint.

Claims

1. A low stress diffusion bonding method suitable for copper / titanium dissimilar materials, characterized in that The low stress diffusion bonding method suitable for copper / titanium dissimilar materials is implemented by the following steps: Step 1: Processing multiple grooves or arrays of circular grooves on the surfaces to be welded of the copper workpiece and the titanium workpiece, respectively. Then, the copper workpiece and the titanium workpiece are cleaned and dried. The grooves or arrays of circular grooves of the copper workpiece are filled with granular materials for adjusting the thermal expansion coefficient, and the grooves or arrays of circular grooves of the titanium workpiece are filled with zirconium oxide particles. Step 2: Use a friction stir head to perform friction stir surface treatment on the surfaces to be welded of the copper workpiece and the titanium workpiece, respectively. During the friction stir surface treatment, the friction stir head speed is controlled to be 220-380 rpm, the travel speed is 20-100 mm / min, the inclination angle is 0-3.5°, and the plunge treatment depth is 0.1-0.8 mm to obtain pretreated copper workpieces and titanium workpieces; Step 3: Grind and polish the pre-treated copper and titanium workpiece surfaces to be welded, place the copper and titanium workpiece surfaces to be welded opposite each other, apply a joining pressure of 2 to 30 MPa, and perform vacuum diffusion bonding in a vacuum diffusion furnace at a temperature of 600 to 900°C, thereby completing a low-stress diffusion bonding between the copper and titanium dissimilar materials. The material of the granular material for adjusting the thermal expansion coefficient in step one is silicon carbide, titanium carbide, tungsten carbide, molybdenum powder, tungsten powder, zirconium tungstate or yttrium tungstate; the particle size of the granular material for adjusting the thermal expansion coefficient and the zirconium oxide particles in step one is 0.01~10μm; the width of the groove in step one is 0.5~1.5mm, and the depth of the groove is 0.1~0.3mm; the diameter of the array circular groove is 0.5~4mm, and the depth of the circular groove is 0.1~0.3mm.

2. The low stress diffusion bonding method suitable for copper / titanium dissimilar materials according to claim 1, characterized in that The material of the copper workpiece in step 1 is pure copper, brass, aluminum bronze or white copper.

3. The low stress diffusion bonding method suitable for copper / titanium dissimilar materials according to claim 1, characterized in that The material of the titanium workpiece in step 1 is pure titanium, TC4 alloy, TC6 alloy, TC11 alloy or TB6 alloy.

4. The low stress diffusion bonding method suitable for copper / titanium dissimilar materials according to claim 1, characterized in that In step three, the pre-treated copper workpiece and titanium workpiece surfaces to be welded are mechanically polished.

5. The low stress diffusion bonding method suitable for copper / titanium dissimilar materials according to claim 1, characterized in that The time for vacuum diffusion connection in step 3 is 5 to 100 minutes.

6. The low stress diffusion bonding method suitable for copper / titanium dissimilar materials according to claim 1, characterized in that In step 3, vacuum diffusion bonding is performed at a temperature of 700-900° C. for 20-50 minutes.

Images