Segregation effect on microstructure stability & mechanical properties of Mg-0.4 wt% Ca alloy

Abstract

Despite the large amount of work done in the last two decades on light weight magnesium (Mg) alloys, there is a lack of systematic and careful study on the effect of segregation on microstructure stability of Mg alloys. In previous studies, small precipitates were found at grain boundaries along with segregation in dilute magnesium alloys. Hence, it was not clear whether grain growth was hindered by grain boundary pinning effect or segregation effect. Furthermore, in earlier studies the amount of segregation was not uniform across the boundaries. Hence, the aim of present study is to study the effect of Ca as a segregating element on the microstructure stability of dilute magnesium alloys. In this context, Mg - 0.4wt% Ca alloys were processed by high pressure torsion (HPT) and extrusion techniques. Ca segregation was observed along the grain boundaries in extruded alloys, whereas no segregation was observed in HPT processed alloys. Microstructure stability experiments show that the grain size of the extruded alloys with grain boundary segregation has not increased to a greater extent after heat treatment. Whereas, the grain size of the HPT alloys without grain boundary segregation has increased quite an extent, hence, its microstructure is least stable with respect to heat treatment.