Investigation of the impact of trace Y addition on mechanical properties, microstructure and fracture behavior of Mg-4Al-2.5Ce-1.5La-0.3Mn-xY (x = 0, 0.1, 0.2, 0.5 wt%) alloys

In this paper, the microstructure evolution, mechanical properties and fracture behavior of Mg-4Al-2.5Ce-1.5La0.3Mn-xY (x = 0, 0.1, 0.2, and 0.5 wt%) alloys with trace Y additions are investigated. The results indicate that the addition of Y significantly refines the bulky acicular phases and massive phases. And with the addition of Y, the second phases lattice-like distributed become more discrete. The comprehensive mechanical properties of Mg-4Al-2.5Ce-1.5La-0.3Mn-0.5Y alloy are optimized at a Y addition of 0.5 wt%, with the ultimate tensile strength (UTS) of 129 MPa and the elongation (EL) of 16%, which are 32% and 45% higher than that of the pristine alloy, respectively. Through fracture analysis, the discrete distribution of fine Al -RE phases in the Mg4Al-2.5Ce-1.5La-0.3Mn-0.5Y alloy contribute to reducing the risk of stress concentrations and improving the plasticity. By performing electron backscattering diffraction (EBSD) analysis near the fracture, the twins dominate the deformation process, while Y induces the formation of a large number of {1012} tensile twins in the alloy to coordinate the plastic deformation. Therefore, a comprehensive analysis reveals that the strengthplasticity improvement consists of two main mechanisms, namely, the second phase optimization and the twin optimization mechanism.