Effect of heat treatment on microstructures and mechanical properties of a cast Mg-Y-Nd-Zr alloy

Microstructures and mechanical properties of Mg-3.5Y-2.5Nd-0.5Zr alloy under various heat treatment conditions were investigated by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), micro-hardness tests and tensile tests. The results showed that the as-cast alloy was mainly consisted of α-Mg, Mg41Nd5, Mg24Y5 and β′(Mg14Nd2Y) phases. After solution treatment at 798 K for 4 h and subsequent aging at 498 K for 34 h, the alloy obtained the remarkable mechanical properties and the ultimate tensile strength, yield strength and elongation were 301 MPa, 202 MPa and 6.9%, respectively. The super tensile properties were mainly attributed to a high volume fraction of fine β′′ and β′ phase which coexisted together in the matrix. Peak-aged at a relatively high temperature, such as 508 K or 523 K, the coarse β′ phase led to a strength decline.