Tailoring bimodal grain structure of Mg-9Al-1Zn alloy for strength-ductility synergy: Co-regulating effect from coarse Al2Y and submicron Mg17Al12 particles

Grain boundary strengthening is an effective strategy for increasing mechanical properties of Mg alloys. However, this method offers limited strengthening in bimodal grain-structured Mg alloys due to the difficultly in increasing the volume fraction of fine grains while keeping a small grain size. Herein, we show that the volume fraction of fine grains (FGs, ∼2.5 µm) in the bimodal grain structure can be tailored from ∼30 vol.% in Mg-9Al-1 Zn (AZ91) to ∼52 vol.% in AZ91–1Y (wt.%) processed by hard plate rolling (HPR). Moreover, a superior combination of a high ultimate tensile strength (∼405 MPa) and decent uniform elongation (∼9%) is achieved in present AZ91–1Y alloy. It reveals that a desired bimodal grain structure can be tailored by the co-regulating effect from coarse Al2Y particles resulting in inhomogeneous recrystallization, and dispersed submicron Mg17Al12 particles depressing the growth of recrystallized grains. The findings offer a valuable insight in tailoring bimodal grain-structured Mg alloys for optimized strength and ductility.