Development of ultra-high strength and ductile Mg–Gd–Y–Zn–Zr alloys by extrusion with forced air cooling

Abstract

Magnesium alloys containing heavy rare earth metals (HRE) have been attracting wide attention due to their remarkable age-hardening response. Extrusion of Mg-HRE alloys generally requires high ram force, leading to heat generation during the extrusion. In this study, by simply utilizing forced air cooling, high strength Mg–8.2Gd–3.8Y–1Zn–0.4Zr (wt%) alloy with good ductility was successfully developed via tailoring the microstructure. The dynamic recrystallization (DRX) ratio, grain size and texture can be controlled by cooling during the extrusion process, that is, the forced air cooling reduces the extrusion temperature and brings about rapid cooling of the extrudate after extrusion. Consequently, the alloy extruded with forced air cooling exhibits high tensile yield strength of 378 MPa, ultimate tensile strength of 436 MPa and high elongation to failure of 12.5% due to a bimodal microstructure consisting of finer DRXed grains with relatively random orientations and coarse unrecrystallized grains with a strong basal fiber texture.