Abstract
In the development of magnesium alloys for high pressure die casting which have excellent high temperature strength, creep properties have been investigated with focusing on calcium addition. Creep tests were performed in the temperature range of 373–473 K and the stress range of 40–100 MPa. The creep resistance of the Mg–Zn alloy at temperature below 440 K is extremely improved with calcium addition. As the concentration of zinc increased, the creep properties tend to deteriorate. In other words, if the alloy contains less than 4 mass%Zn and more than 0.5 mass%Ca, good creep properties is shown below 440 K in the alloy systems. The fine plate precipitates consisting of several atom layers are found in the crept samples which show good creep properties. On the other hand, the coarse precipitates are observed in the samples after creep in alloys without calcium and with calcium crept above 440 K. Improvement of the creep properties by calcium addition is considered to be caused by the precipitation of fine compounds.
