Effect of Al content on microstructural characteristics and tensile properties of extruded Mg–Al–Zn–Ca–Y alloy sheets

This study systematically examines the influence of Al content on the microstructure and tensile properties of extruded SEN (Mg–Al–Zn–Ca–Y) magnesium alloy sheets. Four alloys, SEN1, SEN3, SEN6, and SEN9, containing 1, 3, 6, and 9 wt.% Al, respectively, were investigated. In homogenized billets, grain refinement intensified with increasing Al content, which in turn promoted dynamic recrystallization (DRX) during extrusion. After extrusion, SEN1 and SEN3 exhibited partially recrystallized microstructures with unrecrystallized fractions of 7.3% and 3.5%, respectively, whereas SEN6 and SEN9 were fully recrystallized. The average DRX grain size increased from 8.4 μm in SEN1 to 17.7 μm in SEN6, followed by a slight decrease to 16.9 μm in SEN9, attributed to grain-boundary pinning by second-phase particles and discontinuous precipitates (DPs). With increasing Al content, the area fraction of second phases increased; all sheets contained fragmented second-phase bands aligned with the extrusion direction, while SEN9 additionally exhibited coarse β-phase particles and grain-boundary DPs. The evolution of yield strength with Al content was most strongly associated with the increased contribution of texture strengthening, together with additional contributions from solid-solution strengthening and particle strengthening at higher Al contents, particularly in SEN9. Strain-hardening analysis revealed that SEN6 exhibited the most sustained strain hardening and the greatest elongation. In contrast, SEN9 showed reduced ductility due to early particle-induced cracking associated with coarse β -phase particles. These results demonstrate that an intermediate Al content provides an optimal balance between strength and ductility in extruded SEN alloy sheets by promoting a fully recrystallized, homogeneous microstructure while avoiding coarse, undissolved secondary phases.