An investigation on hot tearing of AZ91 alloys with yttrium additions

Abstract

In this study, the effect of yttrium (Y) content on the hot tearing behavior of the AZ91 + xY alloys was investigated with a constrained rod casting (CRC) apparatus which was equipped with a load sensor and a data acquisition system. The microstructure and the morphology of hot cracks on the surfaces of the alloys were observed by a scanning electron microscope (SEM). The results demonstrate that with increasing Y content, the hot tearing susceptibility of AZ91 + xY alloys is decreased, reaching a minimum value when the alloy contains 1.5 wt%Y, and is further increased with further increasing Y content. In other words, AZ91 alloy (without Y) has the highest hot tearing susceptibility, whereas AZ91 + 1.5 wt%Y has the lowest hot tearing susceptibility. The SEM results further indicate that hot tears that take place during the solidification of AZ91 + xY alloys are mainly due to the liquid film and the solidification compensation force.