Method for improving laser welding performance of CNT / Al composite material through severe plastic deformation processing

Abstract

The invention relates to a method for improving the laser welding performance of a CNT / Al composite material through severe plastic deformation processing, which comprises the following steps of: pre-treating by using a severe plastic deformation processing method, polishing a surface oxide layer, and enhancing the laser welding performance of the CNT / Al composite material by using a carbon nanotube, so as to improve the laser welding performance of the CNT / Al composite material. By adjusting technological parameters of large plastic deformation processing, a reinforced phase carbon nano tube in the CNT / Al composite material is completely damaged, so that a nano Al4C3 phase is generated. When the parameters are certain, the carbon nano tube is completely converted into a nano Al4C3 phase in a large plastic deformation processing mode, so that the large-size brittle and hard Al4C3 phase is prevented from being generated in the laser welding process; the nanometer Al4C3 phase reinforcement can enable stress distribution to be more uniform, and the possibility of fracture of the reinforcement and an interface under the action of stress concentration is reduced; and the pore defect problem of the CNT / Al composite material in the laser welding process is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the field of laser welding, and in particular relates to a method for improving the laser welding performance of a CNT / Al composite material through large plastic deformation processing. Background Art

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

[0003] Among many metal-based composite materials, carbon nanotube-reinforced aluminum-based composite materials have been widely studied due to their low density and high specific strength. However, the poor weldability of carbon nanotube-reinforced aluminum-based composite materials seriously hinders their further practical production and application. Although carbon nanotubes have 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 preparation of the composite material. This results in the suspended C atoms at the damaged part of the carbon nanotube structure reacting violently with the molten Al matrix during laser welding, generating large-sized brittle Al 4 C 3 The grains in the weld area without the pinning effect of carbon nanotubes grow rapidly, and the grain size is much larger than the nanoscale grains of the base material, resulting in a huge difference in the performance of the joint and the base material. The joints of carbon nanotube-reinforced aluminum-based composites after laser welding have obvious pore defects. In addition, the density of carbon nanotubes is lower than that of aluminum, and carbon nanotubes will float and agglomerate in the molten Al liquid, causing crack initiation. This greatly limits the practical application of carbon nanotube-reinforced aluminum-based composites.

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

[0005] The purpose of the present invention is to propose a new welding method to reduce the coarse Al 4 C 3 The generation of phases, pores and cracks.

[0006] The above purpose is achieved through the following technical solutions:

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

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

[0009] Step 2: Process the CNT / Al composite material using a large plastic deformation method to obtain nano-Al 4 C 3 / Al composite materials.

[0010] Step 3: Use wire cutting method to cut the material after large plastic deformation processing.

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

[0012] Step 5: Use a fixture to fix the two processed nano-Al 4 C 3 / Al composite material plate is fixed on the laser welding workbench.

[0013] Step 6: Pass argon gas.

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

[0015] Step 8: On two pieces of Al 4 C 3 Laser welding is performed at the joints of the aluminum / Al composite panels.

[0016] Step 9: Use compressed air to purge the weld to remove carbides precipitated on the surface.

[0017] Step 10: Wait for Al 4 C 3 After the / Al composite material sheet cools to room temperature, it is removed and the welding is completed.

[0018] Furthermore, the large plastic deformation methods used in step 2 include but are not limited to methods such as friction stir processing (FSP), equal channel angular pressing (ECAP), cumulative rolling bond (ARB) and high pressure torsion (HPT).

[0019] Furthermore, in step 3, the processed material is cut into flat plates using a wire cutting method.

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

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

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] When the parameters of the present invention are constant, the carbon nanotubes are completely converted into nano-Al by large plastic deformation processing. 4 C 3 This avoids the formation of large-scale brittle Al phase during laser welding. 4 C 3 Mutually;

[0024] Nano Al 4 C 3 Phase reinforcement can make stress distribution more uniform, reducing the possibility of reinforcement and interface fracture under stress concentration;

[0025] The porosity defect problem of CNT / Al composite materials during laser welding is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the friction stir processing of carbon nanotube reinforced aluminum-based composite materials according to the present invention.

[0027] In the figure, 1 is a carbon nanotube reinforced aluminum matrix composite material plate; 2 is a stirring head; 3 is a nano-Al 4 C 3 Reinforced aluminum matrix composite material (friction stir processing weld); 4 is a stirring head shoulder; 5 is a stirring needle.

[0028] Figure 2 This is a schematic diagram of laser welding on a material after friction stir processing in the present invention. In the figure, 1 is a laser welding seam; 2 is a laser head; 3 is a friction stir processing weld; 4 is a nano-Al 4 C 3 Reinforced aluminum matrix composite material (carbon nanotube reinforced aluminum matrix composite material plate)

[0029] Figure 3 This is a graph showing the Raman spectrum test results of the carbon nanotube reinforced aluminum-based composite material before and after friction stir processing of the present invention.

[0030] Figure 4 This is a comparison diagram of the weld cross-sectional morphology of laser welding of carbon nanotube reinforced aluminum-based composite materials before and after stir friction processing under the same laser welding process parameters in the present invention.

[0031] Figure 5 The microhardness of the carbon nanotube reinforced aluminum-based composite material used in the present invention before and after processing. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1-5 The present invention is further described in detail

[0033] Example:

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

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

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

[0037] Step 3: Figure 1 As shown, a stirring head is installed to stir friction process the carbon nanotube reinforced aluminum matrix composite material plate to obtain nano-Al 4 C 3 Reinforced aluminum matrix composite material. The stirring head rotation speed is 400rpm and 800rpm, the stirring head feed speed is 150mm / min, and the stirring head pressing amount is 0.1mm.

[0038] Step 4: Use a laser welding fixture to weld the friction stir processed nano-Al 4 C 3 Strengthen the fixing of aluminum matrix composite materials.

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

[0040] Figure 3 The Raman test results of the carbon nanotube aluminum matrix composite material before and after the friction stir processing of the present invention are shown in the figure. As can be seen from the figure, the intensity ratio of the D peak to the G peak of the base material is 1.18, and the quality and structure of the carbon nanotubes remain relatively good; after the friction stir processing with the stirring head speed of 400rpm, the intensity ratio of the D peak to the G peak rises to 1.35, the carbon nanotube structure is destroyed, and there is a clear Al 4 C 3 When the rotation speed is 800rpm, the D peak and G peak show the characteristics of steamed bun peaks. 4 C 3 The relative intensity of the peak has exceeded that of the D peak and the G peak, and the structure of the carbon nanotubes has been completely destroyed.

[0041] Figure 4 The figure is a comparison of the cross-sectional morphology of the weld of the carbon nanotube reinforced aluminum-based composite material before and after the friction stir processing under the same laser welding process parameters. Figure 4 As shown in (a), laser welding of carbon nanotube reinforced aluminum matrix composites will produce a large number of pore defects; Figure 4As shown in (b), when laser welding is performed on the material after friction stir processing, no macroscopic porosity defects are observed.

[0042] Figure 5 The microhardness of the carbon nanotube reinforced aluminum-based composite material used in the present invention before and after processing shows that the microhardness of the base material after direct laser welding is about 50HV, and the microhardness of the base material after friction stir processing is about 130HV. The microhardness of the base material after friction stir processing and laser welding far exceeds the microhardness of direct laser welding, and the microhardness is increased by more than 3 times. Friction stir processing greatly improves the mechanical properties of the laser welded joints of carbon nanotube reinforced aluminum-based composite materials.

[0043] The above phenomenon shows that carbon nanotubes can be completely converted into nano-Al through the method of stir friction processing. 4 C 3 phase, avoiding coarse Al 4 C 3 The appearance of the phase solves the problem of a large number of pore defects during laser welding, and improves the mechanical properties of laser welded joints by more than 3 times. Friction stir processing is a method that can improve the laser weldability of CNT / Al composites.

Claims

1. A method for improving the laser welding performance of CNT / Al composite materials by large plastic deformation processing, characterized in that: The method is: pre-treating by large plastic deformation processing method, polishing the surface oxide layer of carbon nanotube reinforced aluminum-based composite material CNT / Al to improve its laser welding performance.

2. The method for improving the laser welding performance of CNT / Al composite materials by large plastic deformation processing according to claim 1, characterized in that: By adjusting the process parameters of large plastic deformation processing, the reinforcing phase carbon nanotubes in the CNT / Al composite material are completely destroyed to produce nano-Al4C3 phase.

3. A method for improving the laser welding performance of CNT / Al composite materials by large plastic deformation processing, characterized in that: The following steps are involved: Step 1: Surface treatment of the CNT / Al composite material plate is performed by grinding with an angle grinder to remove the surface oxide layer; Step 2, processing the CNT / Al composite material by a large plastic deformation method to obtain a nano Al4C3 / Al composite material; Step 3, cutting the material after large plastic deformation processing by wire cutting method; Step 4: Surface treatment is performed on the cut material by grinding it with an angle grinder to remove the surface oxide layer; Step 5, fix the two processed nano-Al4C3 / Al composite material plates on the laser welding workbench using a fixture; Step 6, passing argon gas; Step 7: Set the laser welding start and end positions, defocus, laser head tilt angle, laser scanning speed, and laser average power; Step 8, laser welding is performed at the joint of two Al4C3 / Al composite material plates; Step 9: Use compressed air to purge the weld to remove carbides precipitated on the surface; Step 10: After the Al4C3 / Al composite material plate is cooled to room temperature, it is removed and the welding is completed.

4. The method according to claim 3, characterized in that In step 2, the large plastic deformation methods used include but are not limited to stir friction FSP, equal channel angular pressing ECAP, cumulative rolling ARB and high pressure torsion HPT method.

5. The method according to claim 3, characterized in that: In step 3, the processed material is cut into flat plates using a wire cutting method.

6. The method according to claim 3, characterized in that In step 6, the argon gas flow rate used is 15 L / min.

7. The method according to claim 3, characterized in that In step 7, the laser power used is 1500-3000W, the laser head tilt angle is 10°, the defocus amount is 15mm, and the scanning speed is 0.36m / min.

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