Abstract:The evolution and distribution of Al₂Sm phase in as-extruded AZ61-xSm (x=0, 1.5, 2.0 and 2.5, mass fraction, %) magnesium alloys during semi-solid isothermal heat treatment were investigated. The results showed that when as-extruded AZ61 magnesium alloys were modified with Sm, the smaller and rounder grains were obtained during semi-solid isothermal heat treatment. When the Sm content is 2.0% (mass fraction), the average size of the globular grains reached the smallest value of 90 μm. Although a few Al₂Sm particles existed in the α-Mg grains, most of Al₂Sm particles solidified at the edge of the globular grains with the width of ~20 μm. These phenomena are mainly attributed to the forces acting on Al₂Sm particles in front of the solid-liquid interface, leading to Al₂Sm particles accumulating at the solid-liquid interface and then solidifying at the edge of the globular grains in the quenching process.

Key words: magnesium alloy; rare earth element; semi-solid isothermal heat treatment; Al₂Sm particle