Effects of melt temperature on as-cast structure and mechanical properties of AZ31B magnesium alloy

The effects of melt temperature on the as-cast structure and mechanical properties of AZ31B magnesium alloy were studied through a home-made electrical resistance furnace. The results show that the equiaxed dendrite size of AZ31B magnesium alloy under water-cooled metal cooling is linearly decreased with increasing the melt temperature below 850 °C, whereas the size changes little over 850 °C. The second phases in the microstructure are firstly refined; however, they are coarsened when the melt temperature exceeds 850 °C. With the increase of melt temperature, the tensile strength, yield strength and elongation of AZ31B magnesium alloy samples are rapidly enhanced first, then are slightly declined. When the melt temperature is increased to 850 °C, the tensile strength, yield strength and elongation reach 260 MPa, 75.4 MPa and 27.57%, respectively. The tensile strength, yield strength and elongation are increased by 15%, 13% and 61%, respectively compared with 750 °C. DSC analysis shows that the nucleation temperature is decreased, the critical nucleus radius is lessened with the increase of melt temperature, which increase the degree of supercooling and heterogeneity nucleation rate in melt, and the growth rate becomes larger with the increase of the degree of supercooling. That is the reason why the grain size is first rapidly decreased, and then is little increased.