Microstructure and mechanical properties of 6061 aluminum alloy welded joints by ultrasonic frequency pulsed MIG welding
A ultrasonic frequency pulsed MIG welding method was proposed to solve the problems of multiple porosity defects,coarse microstructure and poor mechanical properties in the MIG welding of 6061 aluminum alloy used in high speed trains.ER4043 aluminum alloy welding wire was used as the filler material,and the influence of different ultrasonic frequency pulse parameters on the microstructure and mechanical properties of the welded joint was studied.It was found that the ultrasonic frequency pulse arc could reduce the size and number of coarse dendrites in the weld zone,increase the area occupied by equiaxed fine grains,and the higher the frequency of ultrasonic pulse,the better the grain refinement effect.As the pulse frequency increased,the columnar dendrites at the edge of the fusion zone of the ultrasonic frequency pulsed MIG weld also became narrower,finer,and more dispersed,and the number of columnar dendrites gradually decreased.On the basis of conventional pulsed MIG,adding ultrasonic frequency pulse current could simultaneously improve the strength and ductility of welded joints.At the frequency of 40 kHz,the tensile strength was highest,reaching 250 MPa,which was 88.3％of the base metal strength,and the elongation rate reached 15.2％.
6061 aluminum alloyultrasonic frequency pulseMIG weldingmicrostructuremechanical property
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