Microstructures and mechanical properties of an ultrathin wall high-pressure die casting Mg-8Zn-8Al (wt%) alloy

Abstract

An ultrathin wall Mg-8Zn-8Al (wt%) alloy was manufactured by high-pressure die casting (HPDC), and exhibits standout strength of ∼ 248 MPa with an acceptable elongation of ∼2.3%. Interestingly, this alloy contains relatively coarse α-Mg grains (∼ 5.6 µm) and ultra-fine β-Mg grains (∼ 0.67 µm), and many nano-sized icosahedral quasicrystal phase (I-phase) particles in eutectic regions. Atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observations reveal possible amorphous regions around I-phase particles, C-containing phase and/or MgO aggregations, and Zn-rich clusters and pyramidal precipitates. Both ultra-fine grains along with the skeleton consisted of nano-sized I-phase particles and solutes including Zn-rich clusters in Mg matrix contribute the ultra-high strength. On the other hand, this work indicates that interaction of alloy melt with CO2 is avoidless during ultra-thin wall HPDC and pyramidal precipitation is possible at least in Zn-containing magnesium alloys.