The Study On AC CMT Welding Process Of AZ31B Magnesium Alloys

In the21stcentury, the balance of resources and the environment as well assustainable development has become the most important humanity issue, has put forwardhigher requirement on the weight of the material. Magnesium alloy is an ideal lightweightmaterial. With its wide range of applications in engineering structures will face thewelding problems. AC CMT technology is an emerging technology, until now, theresearch on the technology for AC CMT welding of magnesium allog is still a blank.In this paper, based on1.5mm thickness of AZ31B magnesium alloy sheet, conductAC CMT and DC CMT two kinds of welding process tests. The metallurgical microscope,tensile testing machine, microhardness tester and other analytical testing methods wereused studying organization and performance of the weld joints with two different weldingprocesses.The result showed that the weld was typical cast structure, and the boundarybetween weld zone and heat affected zone was clear. The heat affected zone was typicaloverheating organization and the heat input would impact the grain. The compositions ofwelding seam wereα-Mg andβ-Mg17Al12. when AC CMT welding, with the increase ofwelding current, or decrease of welding speed, or decrease of EN polar number as EN:EPwas1:1, or increasing EN polar number as EN+EP was14, led to the size of weld zonegrains became larger and larger, the organization of heat affect constantly coarsening andscope gradually extended. During the microhardness test of joint, hardness curve showedthe “W” shape and the hardness of weld area was maximum, followed by the base metaland that of heat affected zone was minimum. The orthogonal design experiment of DCCMT welding showed that the welding speed combated the most significant influence ontensile strength and elongation, arc-length correction with minimal impact. Its optimalwelding parameters as following: welding current was50A, the arc-length corrected was0,the welding speed was450mm·min-1. The best process parameters of AC CMT weldingprocess were as following: the welding current was66A, welding speed was450mm·min-1and EN:EP was7:7. At this time, the tensile strength and elongation were the largest andwere respectively235MPa and9%, achieved96.7%and85.7%of base metal respectivelyand broke in the heat-affected zone.The energy distribution in AC CMT welding process was adjusted by adjusting thenumber of EN and EP wave, minimzing the heat input of base metal to improve theperformance of joints. The joint performance of AC CMT was better than that of DC CMTconnectors.