Microstructure and mechanical properties of a Mg-4Y-3RE alloy processed by thermo-mechanical treatment

Thermo-mechanical treatments consisting of hot extrusion at 573 or 673 K and artificial aging at 473 K were carried out on a Mg-4Y-3RE alloy. The material extruded at 573 K, followed by aging for 2 h, showed fine needle-like precipitates and the high density of a dislocation cell. This material exhibited a high strength of 370 MPa at room temperature. The material extruded at 673 K exhibited a very small grain size of 1.5 μm and fine spherical precipitates. This material showed not only a high strength of about 300 MPa from room temperature to 473 K, but also superplastic behavior at a high strain-rate of 4×10−1 s−1 and at 673 K. Furthermore, a good combination of high strength and high ductility at room temperature was attained for the material extruded at 673 K. These qualities can likely be attributed to the very small grain size.