Dual role of Al2Y phase for heterogeneous microstructure and strength–plasticity synergy in Mg-Y-Al alloys via continuous squeeze casting-extrusion

Abstract

In this paper, the effects of the content and morphology of Al 2 Y phase on the microstructures and mechanical properties of Mg-1.5nY-nAl ( n = 0.5, 1.0, 1.5, 2.0) alloys fabricated by continuous squeeze casting-extrusion(CSCE) process are investigated. The increase in the content of Y and Al elements leads to the formation of primary Al 2 Y particles in the alloys. The exposed {222} close-packed plane of Al 2 Y exhibits a similar crystal structure to that of α-Mg, thereby acting as a nucleation site for α-Mg and significantly refining the as-cast microstructure. During CSCE process, the primary Al 2 Y particles not only trigger particle-stimulated nucleation (PSN) but also exhibit a well-defined orientation relationship with the surrounding recrystallized α-Mg grains, specifically {222} Al2Y //{0001} Mg and < 211 > Al2Y // < 11–20 > Mg . Furthermore, the content and distribution of eutectic Al 2 Y phase markedly affect the dynamic recrystallization (DRX) behavior. The dendritic eutectic Al 2 Y phase is crushed during hot extrusion, hinders the passage of dislocations, and plays a PSN-like role in promoting DRX. Notably, a higher eutectic Al 2 Y content leads to an increased DRX fraction. The alloy designed with the composition of Mg-2.25Y-1.5Al (wt.%) has the best comprehensive mechanical properties, achieving an ultimate tensile strength of 314.3 MPa, a yield strength of 257.6 MPa, and an elongation of 11.6%. This superior performance is attributed to a heterogeneous microstructure consisting of both recrystallized and deformed grains, with heterogeneous structure strengthening identified as the key enabler of the synergy between strength and ductility.