Age hardening characteristics and high temperature tensile properties of Mg-Gd and Mg-Dy alloys

In this study, compositional dependence of age hardening characteristics and high temperature tensile properties is investigated in binary magnesium alloys with 5, 10, 15 and 20 mass%Gd or Dy. Considerable age hardening is recognized in alloys with higher content of Gd or Dy. In case of equal rare earth metal contents, precipitates which play an important role for the age hardening of Mg-Gd alloys are more stable than those of Mg-Dy alloys at elevated temperatures. A Mg-20 mass%Gd alloy, therefore, exhibits remarkable age hardening even at 300°C. Tensile strength of Mg-Gd and Mg-Dy alloys increases linearly with Gd or Dy content and reaches the maximum tensile strength, 310 N/mm2 at 300°C for Mg-20 mass%Gd and 275 N/mm2 at 200°C for Mg-20 mass%Dy. The values are far superior to those of the conventional heat resistant magnesium and aluminum alloys. Elongation of Mg-Gd and Mg-Dy alloys decreases with increase in Gd or Dy content, and the elongation of Mg-20 mass%Gd and-20 mass%Dy alloys is less than 1% below 200°C, whereas the alloys containing 5 and 10 mass% shows higher elongation than 2% at room temperature.