A low-cost Mg-Al-Mn-Zn alloy for automotive road wheel applications

In this study, a new Mg-Al-Mn-Zn alloy (AMZ211) was designed, aided by thermodynamic modeling, for applications in automotive road wheels using forging and flow-forming processes. The AMZ211 alloy was cast and forged in an industrial scale to obtain a forged blank to evaluate its tensile properties and hot formability under high-strain-rates (simulating flow-forming conditions). Multiple characterization techniques, including optical, scanning electron and scanning transmission electron microscopy as well as electron backscatter diffraction, were applied to investigate the microstructural evolution during the processing route. As expected from the alloy design, nano-sized Mn-containing dispersoids formed in a homogeneous manner during homogenization heat treatment, contributing to the formation of refined dynamically recrystallized (DRXed) grains in as-forged microstructure. The as-forged AMZ211 alloy showed better hot formability than as-forged AZ80 Mg alloy under high-strain-rate condition as well as a comparable strength property in relative to the benchmark and more expensive Mg-Zn-Zr alloys. The lower ductility of as-forged AMZ211 alloy may be due to the high twinning tendency of coarse unDRXed domains which were formed as a result of the original coarse-grained microstructure from solidification. The present study provides a low-cost Mg alloy for high-volume automotive road wheel applications.