Effects of thermal treatment on precipitate shape and mechanical properties of Mg-8Gd-4Y-Nd-Zr alloy

Precipitation reactions in a Mg-8Gd-4Y-Nd-Zr alloy have been investigated using TEM, HREM, hardness measurements and tensile testing. Globular beta' precipitates, which were different from the typical plate-shaped beta' precipitates usually observed in Mg-Gd-based alloys, were detected in the 160 degrees C/192 h-aged sample. Instead of dissolution and then precipitating as plate-shaped beta' precipitates, the formed globular beta' precipitates grew up when further aged at 215 degrees C, which resulted in the decrease in strength comparing with that of the 215 degrees C single-stage aged samples. Two-stage ageing treatments on the alloy demonstrated that ageing 192 h at 150 degrees C plus 16 h at 215 degrees C made the ultimate strength and the yield strength improved 17 MPa and 13 MPa, respectively. (C) 2011 Elsevier Ltd. All rights reserved.