Casting in the Semi-Solid State of ZK60 Magnesium Alloy Modified with Rare Earth Addition

摘要

In this work, the casting process under mechanical agitation in the semi-solid state was investigated for the production of ZK60 magnesium alloy modified with the addition of 2.5% wt of mischmetal. The results show that this process enables the production of ingots with homogeneous chemical composition and free of shrinkage, inner defects and internal oxidation. The as-cast microstructure consists of an a-Mg matrix with globular grains reinforced by a grid of distinct intermetallics of Mg-Zn, Mg-Zn-RE and Mg-RE type along the grain boundaries. The yield strength at room temperature undergoes more than 50% increase during direct T5 aging, thus reaching 170 MPa. At 300°C, however, the dispersion of nanometric precipitates does not modify the hot deformation behavior of the aged alloy, which undergoes dynamic recrystallization in a similar manner to the as-cast alloy. DRX at 300°C is fastest for the alloy solution-treated at 500°C.