Semi-Solid Processing and Properties of RE-Containing Mg Alloys

Abstract

The RE-containing Mg alloys usually have big RE-rich intermetallic compounds distributed along grain boundaries. In this paper, a 3 wt.% RE containing Mg alloy is processed by combination of semi-solid slurry-making with ultrasonic vibration (UV) and squeeze casting. Results show that good semi-solid slurry with fine and spherical primary α-Mg particles can be obtained due to the effects of the cavitation and acoustic streaming induced by UV, and the average particle size and average shape factor are about 30 μm and 0.70 respectively. The RE-rich intermetallic compounds are refined and uniformly distributed along grain boundaries. With the increase of squeeze pressure from 0 MPa to 200 MPa during the casting of semi-solid slurry, the tensile strength and the elongation of the as-cast samples are increased continuously, which reach 182 MPa and 8.4% respectively. The microstructure is also analyzed with SEM, TEM, XRD and EDS, and the phase constitutions of this Mg-RE-Zn-Y-Zr alloy are mainly α-Mg matrix, α-Zr, W phase (Mg3Zn2Y3), I phase (Mg3Zn6Y) and T phase ((La,Ce)(Mg1-xZnx)11). The mechanism of refinement of RE-rich intermetallic compounds is also discussed.