Tailoring the tensile properties of AZ91 magnesium alloy via grain refinement

Abstract

Grain refinement of AZ91 alloy was achieved via the addition of a modified Al-B inoculant to the melt, where a pronounced heterogeneous nucleation effect by AlB₂ particles was observed via addition of Al-8 wt-% B master alloy up to 0.3 wt-%. Moreover, hot extrusion remarkably enhanced both strength and ductility via developing an equiaxed microstructure by dynamic recrystallisation (DRX), fragmentation/dissolution of eutectics (containing β-Mg₁₇Al₁₂ compound) during hot deformation, and amending casting defects. Both as-cast and extruded data followed the same Hall–Petch plot, implying that the grain size refinement is the main strengthening mechanism. Accordingly, grain refining via inoculation and thermomechanical processing was found to be a viable approach for the enhancement of strength-ductility trade-off through the improvement of tensile toughness.