Study On Process And Properties Of ZM6Cast Magnesium Alloy MIG Welding

This paper discussed the affect of DC MIG welding process parameters on the weld andmicrostructure of as-cast and heat treated ZM6magnesium alloy combination combining withrepair welding technology of ZM6magnesium alloy. Then take the heat treatment on thewelding joints of as-cast and heat treated ZM6magnesium alloy and study the effect of heattreatment on the microstructure and properties. Then contrast the changes in microstructureand properties before and after heat treatment. Finally, analyze distribution、type andformation mechanism of crack and porosity. Through research, this paper arrives at thefollowing conclusions:(1) The effect of welding process parameters on the as-cast and heat treated ZM6magnesium alloy was consistent. With the increase of current, the weld width and depthincrease. When the current is small, with the increase of current; the welding seam decreases,then current increases, the welding seam change little. With increase of voltage, the weldincrease, the weld depth first increase and then decrease. When the voltage is small, with theincrease of voltage; the welding seam decreases, then voltage increases, the welding seamchange little. With increase of welding speed, the weld width and welding seam decrease.(2) Before the heat treatment, the weld crystal grains of as-cast and heat treated weldingjoint are isometric crystal, β-Mg17Al12is founded at boundary and interior of the grains. Themorphology of β-Mg17Al12in heat treated welding joint is smaller and more decentralizedthan as-cast magnesium alloy welding joint. After heat treatment, the β-Mg17Al12in the twokinds of joints is smaller, the quantity is larger, the performance is improved.(3) Before and after heat treatment, the phases in HAZ of two welding joints areconsistent with base metal. In the welding joint of as-cast state ZM6magnesium alloy, thegrain coarsening of HAZ is not obvious, the second phase in grain boundary of the incomplete fusion zone disappear, the dislocations within grain disappear, the second phases that are fineand showing punctuate are distributed in the grain. After heat treatment, the continuoussecond phases in grain boundary of HAZ are replaced with discontinuous second phases.There are two phase in grains: dot phase and clusters phase. The dislocation tangles arefounded in grains of HAZ in welding joint of heat treated ZM6magnesium alloy, the quantityof clusters precipitated phase is decreased. The phases have no obvious change.(4) The tensile strength is more than90%of base metal. And tensile strength is improvedafter heat treatment.(5) The ZM6was welded by DC MIG and the welding wire is WE-33M. There are crackand pores in the welding joints the pores were mainly hydrogen holes. it was dispersed on theweld surface, weld center, fusion line and root flaw. The crack was hot cracking, the produceprobability in weld center was higher.