Microstructure, Texture And Their Effect On Tensile Properties Of 6016 Aluminum Alloy Laser Welded Joints

In this paper,laser beam butt welding was carried out with 1mm thick6016 automotive aluminum alloy plate to study the microstructure and texture of welded joints under different welding process parameters,what’s more,their effects on tensile properties of welded joints.The correlation between welding process parameters,microstructure,texture and tensile properties was developed based on the EBSD results.And it will provide reference for welding joints regulation and property improvement.The results are as follows:The typical microstructure of the 6016 aluminum alloy laser welded joint and the influence of welding process parameters on the microstructure were studied.The weld area consisted of columnar dendrites and coarse equiaxed dendrites;some beneficial second phase such as Mg₂Si andαAl₁₅（FeMn）₃Si₂ was found in the grain interior and boundary of the weld metal.The welding process parameters have a significant effect on the grain structure and the second phase of the welded joint.As the laser power increased,the equiaxed ratio in WM increased,the ratio of second phase increased while its dimension changed little;with the increase of welding speed,equiaxed ratio of WM increased and then decreased,meanwhile,the ratio of second phase and its size decreased,as the defocus increased,the equiaxed ratio increased,but the ratio of second phase and its size both increasedThe mechanical properties test showed that the WM of 6016aluminum alloy had obvious softening,and the tensile strength of the welded joint was 170 MPa（74.2%of the BM）,the elongation was 3.94%（16.0%of the BM）.The fracture morphology showed a typical ductile fracture,and the fracture location was in the weld zone.As the equiaxed ratio in WM increased,the tensile strength of welded joints increased;with the ratio of second phase increased（or the decrease in the size of second phase）,the average hardness of the WM increased.Strong cubic texture（{001}<100>）was observed in columnar dendrites in the 6016 aluminum alloy laser welded joint,but the equiaxed dendrites region was randomly oriented.The welding process parameters did not alter texture in the WM but had an effect on the mud of columnar crystal.As the laser power increased,the mud of columnar crystal decreased,with the increase of welding speed,the mud of columnar crystal rose;as defocus increased,the mud of columnar crystal decreased f.Tensile test results showed that as mud of columnar crystal increased,the elongation decreased obviously.By increasing the laser power and defocus,furthermore minimizing the welding speed,the structure of laser welded joint was successfully optimized under the welding process of laser power of 4.0 kW,welding speed of 2.8 m/min and defocus of+20 mm,and the properties was further improved.The results showed that,compared to the typical laser welded joint of the 6016 aluminum alloy,the equiaxed ratio of the laser welded joint after optimization increased from 30.8%to 40.2%,and the mud of columnar crystal decreased from 11.5 to 7.8.Tensile test results showed that the tensile strength of welded joints has increased from 170 MPa to187 MPa,and the elongation had increased from 3.9%to 5.3%.