Effect of Gd addition on the microstructure and age hardening behavior of Mg-6Zn-1Mn-4Sn (wt.%) alloy

The microstructure evolution and age hardening behavior of Mg-6Zn-1Mn-4Sn (wt.%, ZMT614) through various Gd addition were investigated. The as-cast ZMT614 alloy was mainly composed of Mg2Sn, Mg7Zn3 and alpha-Mg solid solution, and new MgSnGd phases were detected with Gd addition. The MgSnGd phase nucleated prior to Mg2Sn during solidification, resulting in consumption of Sn element and reduction of Mg2Sn phase. Owing to the pinning effect of MgSnGd phase, some dislocations were preserved during solution treatment. The retained dislocations could act as heterogeneous nucleation sites for the rod-like beta(1)precipitates. A trace of Gd addition could enhance the peak hardness and shorten the peak aging time, while excessive Gd addition would weaken the age hardening response. The ZMT614-0.2Gd alloy exhibited the optimum mechanical properties with yield strength of 373 +/- 4 MPa and ultimate tensile strength of 405 +/- 6 MPa. (C) 2020 The Author(s). Published by Elsevier B.V.