Research On Laser Welding Process Of 7A52 High-strength Aluminum Alloy Linearly Thickened Plate

7A52 high-strength aluminum alloy is mainly used in aerospace,automobile and other fields due to its excellent mechanical properties and light weight.In order to minimize its quality under the premise of meeting the strength requirements,it is a study hotspot in recent years to weld plates with continuous-thickness changes.Because of its high energy density and high efficiency,laser welding has become a better choice for aluminum alloy welding.However,the current research on laser welding of aluminum alloy materials is mainly focused on equal-thickness plates,and less on the laser welding process of variable-thickness plates.This subject takes linear thickening 7A52 high-strength aluminum alloy plate as the research object.The research on welding thick plates with constant parameters(constant power,constant speed)and variable parameters(continuous variable power,continuous variable speed)has been carried out.The specific research work is as follows:(1)Build the laser welding system platform.Use the fiber laser welding head with the output head type HHBH to match the ABB robot arm,and the multi-degree-of-freedom welding system increases the equipment flexibility;the independently designed fixture is fixed on the dual-track variable speed sliding platform module.Through compiling the program to control the moving speed and acceleration of the platform,and control the continuous change of the welding speed;adjust the power and speed to perform fixed and variable parameter welding on the linear thickening 7A52 high-strength aluminum alloy plate.(2)At the thin end and the thick end of the weld,a small piece of 10x5 mm in size is taken as the observation sample by wire cutting,inlaid into a cylinder,polished with sandpaper,polished by a polishing machine,corroded by hydrofluoric acid,and observed by a metallographic microscope.Structure,pores,cracks;ZEISS Gemini 300 field emission scanning electron microscope(SEM)was used to observe the distribution of visual defects in welds at different thickness positions.(3)According to the experimental results and test results,analysis of the welding process due to the input energy and thickness mismatch,energy density changes,resulting in the thin end welds collapse through penetration and penetration,thick end welds do not penetrate and bulge,the weld structure is coarse,The formation mechanism of problems such as the concentrated distribution of pores and the extension and intersection of cracks.Welding is performed by changing the input energy through three methods of continuous variable power,continuous variable speed,and power-speed co-continuous change,observe the weld morphology,detect the weld structure,welding defects,and clarify the power change interval and the speed change interval.Explore the coupling relationship between laser power,welding speed,thickness,and energy density to achieve uniform penetration of welds at different thickness positions of the linear thickened 7A52 high-strength aluminum alloy plate by laser welding,and solve the problem of coarse weld structure,concentrated pore distribution and crack extension to improve the quality of welding.