Strengthening Mechanisms of Cast Mg-La-Zr and Mg-Ce-Zr Alloys

Abstract

In the present study, tensile and creep properties of cast Mg-La-Zr and Mg-Ce-Zr alloys were examined and the microstructures of the alloys were observed by optical microscopy, TEM, and Cs-STEM to evaluate creep and work hardening characteristics. The room temperature tensile properties, plotted with lanthanum or cerium contents, did not reveal significant differences between the alloys except for slightly lower elongation for Mg-Ce-Zr alloys. However, at 150˚C, the values of tensile strength for Mg-Ce-Zr alloys were higher than those for Mg-La-Zr alloys, while the values of elongation for Mg-Ce-Zr alloys became significantly lower than those for Mg-La-Zr alloys. It was also found that Mg-Ce-Zr alloys tested at 150˚C exhibited a higher work hardening rate than Mg-La-Zr alloys. In creep curves, Mg-La-Zr alloys exhibited an initial strain after which the direction of curves abruptly changed to almost horizontal during creep testing, whereas Mg-Ce-Zr alloys did not exhibit the initial strain. It was found that Mg-Ce-Zr alloys contained numerous stacking faults on（0001）of the primary α-Mg grains, while Mg-La-Zr alloys did not, and these might have contributed to the differences in creep and work hardening characteristics.