Mechanical behavior of a lanthanum-doped magnesium alloy at different strain rates

The mechanical behavior of a lanthanum doped Mg alloy, AZXE7111, (Mg–7Al–1Zn–1Ca–1La, all in wt%) extruded at different temperatures has been investigated under both quasi-static (strain rate ~1×10−3s−1) and dynamic (strain rate ~4×103s−1) compressive loading. Comparison has been made against the experimental results of two conventional Mg alloys, AZ91E and WE43. It was observed via transmission electron microscopy (TEM) that the nanoscale intermetallic compounds of Al2Ca and Al11La3, have presumably formed during the hot extrusion process. These compounds are believed to contribute significantly to the strength by reducing the grain size and acting as dislocation barriers. Additionally, twinning has been considered as the main mechanism for the higher strain hardening rate at high strain rates than that at low strain rates. It has been found that the ultimate strength of the alloy is only ~10% higher at dynamic loading rate than at quasi-static loading rate. Localized micro-shear fracture was observed and adiabatic shear mode was suggested by further examination of dynamically loaded specimens. The shear localization is further discussed in detail and it is suggested that reduced strain hardening rate is responsible for shear localization and subsequent fracture at both low and high strain rates.