A method for improving laser welding performance of CNT / Al composite material by large plastic deformation processing

Abstract

This invention discloses a method for improving the laser welding performance of CNT / Al composite materials through large plastic deformation processing. The method involves pretreatment using large plastic deformation processing, followed by grinding of the surface oxide layer to enhance the laser welding performance of the carbon nanotube-reinforced aluminum matrix composite (CNT / Al). By adjusting the process parameters of large plastic deformation processing, the reinforcing carbon nanotubes in the CNT / Al composite material are completely destroyed to generate nano-Al4C3 phase. With fixed parameters, large plastic deformation processing completely transforms carbon nanotubes into nano-Al4C3 phase, avoiding the formation of large-sized, brittle Al4C3 phase during laser welding. The nano-Al4C3 phase reinforcement allows for more uniform stress distribution, reducing the possibility of fracture at the reinforcement and interface under stress concentration. This effectively reduces porosity defects in the CNT / Al composite material during laser welding.

Description

Technical Field

[0001] This invention belongs to the field of laser welding, specifically relating to a method for improving the laser welding performance of CNT / Al composite materials through large plastic deformation processing. Background Technology

[0002] Compared with traditional welding methods, laser welding has the advantages of low cost, low heat input, small heat-affected zone, large weld pool depth, fast welding speed, small welding deformation, and easy automation and flexible production.

[0003] Among various metal matrix composites, carbon nanotube-reinforced aluminum matrix composites have been widely studied due to their low density and high specific strength. However, the poor weldability of carbon nanotube-reinforced aluminum matrix composites seriously hinders their further practical production applications. Although carbon nanotubes possess extremely high chemical stability and a melting point much higher than that of the Al matrix, the carbon nanotube structure is inevitably damaged during the composite material preparation process. This leads to a rapid and violent chemical reaction between the suspended C atoms at the damaged carbon nanotube structures and the molten Al matrix during laser welding, generating large-sized, brittle, and hard Al4C3 phases. The grains in the weld region, lacking the pinning effect of carbon nanotubes, grow rapidly, with grain sizes much larger than the nanoscale grains of the base material, resulting in significant differences in the properties of the joint and the base material. The joints of carbon nanotube-reinforced aluminum matrix composites exhibit obvious porosity defects after laser welding. Furthermore, the lower density of carbon nanotubes compared to aluminum causes them to float and agglomerate in the molten Al, leading to crack initiation. This greatly limits the practical application of carbon nanotube-reinforced aluminum matrix composites.

[0004] There is an urgent need to find a method to improve the laser welding performance of carbon nanotube-reinforced aluminum matrix composites. Summary of the Invention

[0005] The purpose of this invention is to address the problem of poor laser welding performance of carbon nanotube-reinforced aluminum matrix composites by proposing a new welding method to reduce the generation of coarse Al4C3 phases, pores, and cracks.

[0006] The above objective is achieved through the following technical solution:

[0007] A method for improving the laser welding performance of CNT / Al composite materials through large plastic deformation pretreatment includes the following steps:

[0008] Step 1: Perform surface treatment on the CNT / Al composite material board by grinding with an angle grinder to remove the surface oxide layer.

[0009] Step 2: The CNT / Al composite material is processed using a large plastic deformation method to obtain nano-Al4C3 / Al composite material.

[0010] Step 3: Cut the material after large plastic deformation using wire cutting.

[0011] Step 4: Perform surface treatment on the cut material by grinding with an angle grinder to remove the surface oxide layer.

[0012] Step 5: Use a clamp to fix the two treated nano-Al4C3 / Al composite material plates onto the laser welding worktable.

[0013] Step 6: Pour in argon gas.

[0014] Step 7: Set the laser welding start and end positions, defocusing amount, laser head tilt angle, laser scanning speed, and average laser power.

[0015] Step 8: Perform laser welding at the joint of the two Al4C3 / Al composite material plates.

[0016] Step 9: Use compressed air to blow away the weld seam and remove the carbides precipitated on the surface.

[0017] Step 10: After the Al4C3 / Al composite material sheet has cooled to room temperature, remove it. Welding is now complete.

[0018] Furthermore, the large plastic deformation methods used in step 2 include, but are not limited to, friction stir (FSP), equal channel angle extrusion (ECAP), cumulative roll forming (ARB), and high pressure torsion (HPT).

[0019] Furthermore, in step 3, wire cutting is used to cut the processed material into flat sheets.

[0020] Furthermore, the argon flow rate used in step 6 is 15 L / min.

[0021] Furthermore, in step 7, the laser power used is 1500-3000W, the laser head tilt angle is 10°, the defocusing amount is 15mm, and the scanning speed is 0.36m / min.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] With the parameters set in this invention, carbon nanotubes are completely transformed into nano-Al4C3 phase through large plastic deformation processing, which avoids the generation of large-sized brittle Al4C3 phase during laser welding.

[0024] Nano-Al4C3 phase reinforcement can make the stress distribution more uniform and reduce the possibility of fracture of the reinforcement and interface under stress concentration.

[0025] It effectively reduces the porosity defect problem of CNT / Al composite materials during laser welding. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the carbon nanotube-reinforced aluminum matrix composite material processed by friction stirring according to the present invention.

[0027] In the figure, 1 is a carbon nanotube reinforced aluminum matrix composite plate; 2 is a stirring head; 3 is a nano-Al4C3 reinforced aluminum matrix composite (friction stir weld); 4 is the shoulder of the stirring head; and 5 is the stirring pin.

[0028] Figure 2 This diagram illustrates laser welding on a material processed by friction stir, as described in this invention. In the diagram, 1 represents the laser weld seam; 2 represents the laser head; 3 represents the friction stir weld seam; and 4 represents the nano-Al4C3 reinforced aluminum matrix composite material (carbon nanotube reinforced aluminum matrix composite material plate).

[0029] Figure 3 The image shows the Raman spectra of the carbon nanotube-reinforced aluminum matrix composite material before and after the friction stir processing of this invention.

[0030] Figure 4 This is a comparison of the weld cross-sectional morphology of carbon nanotube-reinforced aluminum matrix composites before and after laser welding under the same laser welding process parameters.

[0031] Figure 5 The microhardness of the carbon nanotube-reinforced aluminum matrix composite material used in this invention before and after processing. Detailed Implementation

[0032] The following is in conjunction with the appendix Figure 1-5 The present invention will be described in further detail.

[0033] Example:

[0034] A method for improving the laser welding performance of CNT / 2024Al composite materials through friction stir processing specifically includes the following steps:

[0035] Step 1: Use an angle grinder to treat the surface of the 200mm×100mm×6mm CNT / 2024Al composite material plate to remove the oxide layer.

[0036] Step 2: Fix the carbon nanotube reinforced aluminum matrix composite plate using a friction stir welding fixture.

[0037] Step 3, as follows Figure 1As shown, a stirring head was installed to perform friction stir processing on a carbon nanotube-reinforced aluminum matrix composite plate to obtain a nano-Al4C3-reinforced aluminum matrix composite material. The stirring head rotation speed was 400 rpm and 800 rpm, the stirring head feed speed was 150 mm / min, and the stirring head downward pressure was 0.1 mm.

[0038] Step 4: Fix the nano-Al4C3 reinforced aluminum matrix composite material sheet after friction stir processing using a laser welding fixture.

[0039] Step 5, as follows Figure 2 As shown, laser welding was performed at the position after friction stir processing. The laser power was 2000W, the laser head tilt angle was 10°, the defocusing amount was 15mm, and the scanning speed was 0.36m / min.

[0040] Figure 3 The figures show the Raman spectral analysis results of the carbon nanotube aluminum matrix composite material before and after friction stir processing according to this invention. As can be seen from the figure, the intensity ratio of the D peak to the G peak in the parent material is 1.18, indicating that the quality and structure of the carbon nanotubes are well maintained. After friction stir processing at a stirring head speed of 400 rpm, the intensity ratio of the D peak to the G peak increases to 1.35, indicating that the carbon nanotube structure is damaged and a distinct Al4C3 phase appears. When the speed is 800 rpm, the D peak and G peak exhibit a peak-like characteristic, and the relative intensity of the Al4C3 peak exceeds that of the D peak and G peak. At this point, the structure of the carbon nanotubes has been completely destroyed.

[0041] Figure 4 This image shows a comparison of the weld cross-sectional morphology of carbon nanotube-reinforced aluminum matrix composites before and after laser welding under the same laser welding process parameters, according to the present invention. Figure 4 As shown in (a), laser welding of carbon nanotube-reinforced aluminum matrix composites produces a large number of porosity defects; as Figure 4 As shown in (b), no macroscopic porosity defects were observed when laser welding was performed on the material after friction stir processing.

[0042] Figure 5 The microhardness of the carbon nanotube-reinforced aluminum matrix composite material used in this invention before and after processing was determined. The results showed that the microhardness of the base material after direct laser welding was approximately 50 HV, while the microhardness after friction stir processing (FSM) was approximately 130 HV. The microhardness of the material after FSM and laser welding significantly exceeded that of direct laser welding, increasing by more than three times. FSM greatly improved the mechanical properties of the laser-welded joint of the carbon nanotube-reinforced aluminum matrix composite material.

[0043] The above phenomena indicate that friction stir processing can completely transform carbon nanotubes into nano-Al4C3 phase, avoiding the formation of coarse Al4C3 phase while solving the problem of numerous pore defects generated during laser welding, and improving the mechanical properties of the laser-welded joint by more than three times. Friction stir processing is a method to improve the laser weldability of CNT / Al composite materials.

Claims

1. A method for improving laser welding properties of CNT / Al composites processed by severe plastic deformation, characterized by, The method is as follows: By adjusting the process parameters of large plastic deformation processing, the reinforcing phase carbon nanotubes in CNT / Al composite materials are completely destroyed to generate nano-Al4C3 phase, thereby reducing the porosity defects of CNT / Al composite materials during laser welding.

2. A method for improving laser welding properties of CNT / Al composites processed by severe plastic deformation, characterized by, Includes the following steps: Step 1: Perform surface treatment on the CNT / Al composite material board by grinding with an angle grinder to remove the surface oxide layer; Step 2: The CNT / Al composite material is processed using a large plastic deformation method to obtain nano-Al4C3 / Al composite material; Step 3: Cut the material after large plastic deformation using wire EDM. Step 4: Perform surface treatment on the cut material by grinding with an angle grinder to remove the surface oxide layer; Step 5: Use a clamp to fix the two treated nano-Al4C3 / Al composite material plates onto the laser welding worktable; Step 6: Purge with argon gas; Step 7: Set the laser welding start and end positions, defocusing amount, laser head tilt angle, laser scanning speed, and average laser power; Step 8: Perform laser welding at the joint of the two Al4C3 / Al composite material plates; Step 9: Use compressed air to blow away the weld seam and remove the carbides precipitated on the surface; Step 10: After the Al4C3 / Al composite material sheet has cooled to room temperature, remove it. Welding is now complete.

3. The method of claim 2, wherein, In step 2, the large plastic deformation methods used include friction stir (FSP), equal channel angle extrusion (ECAP), cumulative roll forming (ARB), or high pressure torsion (HPT).

4. The method according to claim 2, characterized in that, In step 3, wire cutting is used to cut the processed material into flat sheets.

5. The method according to claim 2, characterized in that, In step 6, the argon flow rate used is 15 L / min.

6. The method according to claim 2, characterized in that, In step 7, the laser power used is 1500-3000W, the laser head tilt angle is 10°, the defocusing amount is 15mm, and the scanning speed is 0.36m / min.

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