Characterization and strengthening effects of γ′ precipitates in a high-strength casting Mg-15Gd-1Zn-0.4Zr (wt.%) alloy

1 wt.% Zn addition introduced additional basal gamma' precipitates to the Mg-15Gd-0.4Zr (wt.%) alloy. Based on the detailed analysis of the precipitates and tensile properties evolution of the alloys, the composite beta' and gamma' precipitates provided much stronger strengthening effects than the only beta' precipitates, even when the latter one had higher number density. The results imply that even a few gamma' precipitates can introduce a composite strengthening effect with the beta' precipitates. Meanwhile, the composite beta' and gamma' precipitates effectively strengthened the grain interior and hindered the twining during the tensile tests. Finally, the alloy containing the composite precipitates exhibited yield strength (YS) of 288 MPa and ultimate tensile strength (UTS) of 403 MPa which were only 232 MPa and 296 MPa, respectively, in the alloy containing only IT precipitates. (C) 2017 Elsevier Inc. All rights reserved.