Research On Laser Welding & Laser-MIG Hybrid Welding Of 7A52 Aluminum Alloy

The 7A52 aluminum alloy is an Al-Zn-Mg based high strength alloy,and it is prone to form defects such as porosity,joint softening and large deformation during traditional arc welding.Laser welding and laser-arc hybrid welding have developed rapidly in recent years due to their high welding efficiency and good quality.In order to explore the laser welding and laser-arc hybrid welding process of 7A52 aluminum alloy,in this study,fiber laser welding and laser-MIG hybrid welding of 7A52 aluminum alloy was investigated.First,doing research on high power laser welding of 7A52 aluminum alloy.It was found that when the laser power is 7k W,welding speed is 2.1m/min,defocusing distance is-2mm &laser power is 6k W,welding speed is 1.2m/min,defocusing distance is 0mm,a good welding appearance can be obtained.The control variable method was used to analyze the influence of each process parameter on the weld formation.When the base metal is welded through and without the gasket added to the back of the weld,the surface of the laser weld seam will inevitably subside,and its value will be about 1-2mm.Analysis of microstructure and mechanical properties of well-formed welds.An equiaxed grain structure with snow-flower like features was found within the weld,while a fine grain region located near the fusion line and a transition area with coloumnar grains in between.EDS analysis confirmed that the Zn and Mg compositions within the weld joint were about 1%-2% lower than the base material.Lower micro-hardness value was also achieved in such areas compared to the base material and its value is about 95 HV.The longitudinal micro-hardness distribution in the center of the weld is uniform.The tensile strength of the joint is about 320-330 MPa,the elongation is about 3.2%,and the fracture mode is microporous aggregate fracture.Laser welding has higher requirements on the assembly accuracy of the base material and the obtained weld seam is prone to collapse,in order to improve the welding process,doing research on laser-MIG hybrid welding of 7A52 aluminum alloy.It was found that when the laser power is 7k W,welding speed is 1.8m/min,defocusing distance is-2mm,welding current is 220 A & laser power is 6k W,welding speed is 1.5m/min,defocusing distance is-2mm,welding current is 180 A,a good welding appearance can be obtained.The control variable method was used to analyze the influence of each process parameter on the weld formation.MIG hybrid welding can effectively suppress the welding surface from sinking due to the welding wire’s molten filling,but when the welding current is too small or the defocusing distance is less than-4mm,the welding surface will still sink.The microstructure of the welding joint is similar to that of laser welding,but the width of the heat affected zone and the width of the columnar crystal region are larger than that of the laser welding joint.The micro-hardness of the upper center of the weld is lower than that of laser welding,and its value is about 85 HV.The micro-hardness of the upper arc region of the weld center is lower than that of the lower laser region.The tensile strength of the joint is about 300-310 MPa,the elongation is about 2.8%,and the fracture mode is still microporous aggregate fracture.7A52 aluminum alloy is prone generate porosity during welding process,the influence of process parameters on the weld porosities was studied through statistic quantification of the porosity area fraction and distribution of the porosities size in this article.Although the laserMIG hybrid welding can reduce process porosities,it increases the source of hydrogen,resulting in an increment of the small-sized hydrogen porosities.Process porosities can be increased with insufficient protecting gas input,positive laser defocusing distance as well as too high laser power.It worth noting that hydrogen porosities are typically round,with relative smooth inner walls,and similar Zn and Mg composition to the weld.On the contrary,the process porosities are normally irregular shaped,with step-like features found in the the inner walls,and higher Zn,Mg elements in the inner wall than its weld counterparts.