LAUSR

Abstract In this work, the role of Al addition in modifying the microstructure and mechanical properties of the Mg-1.0Ca-xAl (x = 0.6, 1.0 wt%; termed as XA10 and XA11, respectively) based alloys has been systematically investigated. Microstructural examination showed that, when the Al content is low, the Al and Ca atoms were inclined to segregate to the dislocation lines in the XA10 sample. As a result, the mobility of dislocation was restrained and the dynamic recovery behavior was hindered, which leads to a low degree of dynamic recrystallization. When the Al content is high, in contrast, no apparent Ca/Al segregations along dislocations have been found in XA11-0 extrusion billet during the whole stages of processing, which results in the enhanced dislocation mobility. Consequently, the recovery of dislocations and dynamic recrystallization rate can be largely enhanced at the earlier stage of extrusion. More importantly, subsequently formed high density Guinier-Preston (G.P.) zones and nano-disk Al2Ca phases in the high-Al content Mg sample can play an effective role in inhibiting the growth of subgrains and dynamically recrystallized (DRXed) grains, which enhance the thermal stability of high density low angular grain boundaries (LAGBs) in the later extrusion stage. The high density nano-disk phases, high volume fraction of DRXed grains, as well as the high density LAGBs in the un-DRXed grains, can together contribute to both high strength and good elongation of the XA11 sample. The findings lead to the controllable Mg-Ca based alloy designing strategy that can improve the strength and ductility simultaneously.