No abstract

A Mg-11Gd-4.5Y-1.5Zn-1Nd-0.5Zr alloy with high-strength and heat-resistance has successfully been prepared by hot extrusion and subsequent ageing. It exhibits an ultimate tensile strength of 473 MPa, 0.2% proof stress of 373 MPa and elongation to failure of 4.1% at room temperature. At 250 °C, this alloy shows an ultimate tensile strength of 369 MPa, 0.2% proof stress of 316 MPa and elongation to failure of 6.3%. Its good mechanical properties and thermal stability are attributed to the dispersion of large volume fraction of 14H-LPSO phase, small α-Mg grains, basal-fiber texture and dense distribution of precipitates at the grain boundaries and inside the grains.

The Mg-11Gd-4.5Y-1Nd-1.5Zn-0.5Zr (wt.%) alloy was pre-aged prior to hot extrusion.Pre-ageing treatment introduced uniform distribution of plate-like Mg 5 RE precipitates, which transformed into nano-scale globular Mg 5 RE particles by split and spheroidization during hot extrusion. These globular Mg 5 RE particles contributed to continuous dynamic recrystallization by promoting the evolution of low misorientation sub-grain boundaries to high misorientation grain boundaries and caused grain refinement through grain boundary pinning. The improved mechanical properties were ascribed to the grain refinement, globular Mg 5 RE and LPSO precipitates. The ratio of compressive to tensile yield strength is 1.2. The yield strength asymmetry was attributed to the deformation asymmetry of LPSO phase and non-isotropic deformation behaviours of Mg matrix in tension and compression.