Aging Characteristics and High Temperature Tensile Properties of Mg-Gd-Y-Zr Alloys

The individual contributions of Gadolinium and Yttrium to age hardening and high temperature strength of magnesium alloys containing both elements are investigated using alloys containing different Gd:Y mole ratios of 1:0, 3:1, 1:1, 1:3 and 0:1 with a constant Y+Gd content of 2.75 mol%. All investigated alloys exhibit remarkable age hardening by precipitation of β′′ phase with DO19 crystal structure and β′ phase with bco crystal structure even at aging temperatures higher than 200°C. Both precipitates are observed in peak-aged specimens. The precipitates contributing to age hardening are fine and their amount increases as Gd content increases, and this results in increased peak hardness, tensile strength and 0.2% proof stress but decreased elongation. On the other hand, higher Y content increases the elongation of the alloys but results in decreased strength.