Microstructures and mechanical properties of the Mg-8Gd-4Y-Nd-Zn-3Si (wt%) alloy

Microstructures and mechanical properties of Mg-8Gd-4Y-Nd-Zn-3Si alloy were systematically investigated using OM, SEM, XRD, TEM, hardness measurements, tensile and resonance test. The as-cast microstructure consists of α-Mg, Mg3(GdYZn), Mg12(GdY)Zn, Mg2Si, Gd5Si3 and YSi2 phases. The long period stacking ordered (LPSO) structure is found in the as-cast sample, which disappears after solution treatment. The mechanical properties of the extruded-T5 alloy are as follows: Young's modulus E=58.5 GPa, yield tensile strength σ0.2=328 MPa, ultimate tensile strength σb=386 MPa and elongation δ=5.9%. The high Young's modulus of the alloy is attributed to the existence of Mg2Si, Gd5Si3 and YSi2 compounds with high Young's modulus. The weakening of age hardening response is ascribed to the formation of vast Gd5Si3 and YSi2 compounds, which consumed plenty of rare earth atoms in the matrix and decreased the amount of β″ and β′ precipitates.