Cooperative effect of Mg and Si contents on the microstructural evolution, mechanical performance, and deformation behavior of cast Al–Li–Mg–Si alloys

Abstract

In this study, the cooperative effect of Mg and Si contents on the microstructural evolution, mechanical properties, and deformation behavior of the cast Al–Li–Mg–Si alloys is investigated. Five different Al–Li–Mg–Si alloys are prepared by conventional casting method, which are referred to as Alloy A-E. The results show that with the increase in the Mg content, the amount of lath-like Mg2Si precipitates and bulk-like AlLiSi particles increases, which leads to an improvement in the strength and ductility of alloys. The amount of intergranular Si-rich phases in Alloy D increases with the increase in the Si content. Further, a higher Si content in Alloy E promotes the formation of bulk-like AlLiSi. The geometric phase analysis (GPA) results reveal strain partitioning behavior at the interface of Mg2Si precipitates and AlLiSi particles, which follows the Orowan looping or dislocation cutting strengthening mechanism. The geometrically necessary dislocation (GND) density calculation results suggest that the lath-like Mg2Si precipitates play a critical role in the deformation behaviors of Alloy A-C. The hindering effect of lath-like Mg2Si precipitates on the movement of dislocations decreases the GND density gap between high-angle grain boundaries or junctions and grain interior and improves the resistance to deformation. However, the deformation behaviors of Alloy D and E with higher Si content are mainly governed by the intergranular Si-rich phases. Finally, a methodological framework is established to elucidate the effect of precipitates and/or intergranular phases on the deformation behaviors of materials using a combination of GPA and GND density calculation methods.