Microstructure and properties of Mg-Nd-Zn-Zr alloys

Abstract

[Abstract]: One of the limitations of magnesium alloys is their low mechanical properties at elevated temperatures. In order to improve the creep strength, rare earth element neodymium Nd is added to Mg-0.3Zn-0.32Zr alloy. A significant grain refinement has already been achieved by the Zr addition in the base metal. The inclusion of Nd further reduces grain size from 120 m to 75 m. When the Nd content is less than 1%, the Nd is fully dissolved into Mg matrix. Increasing the Nd addition to 1.6% leads to a precipitation of Mg12Nd intermetallic phase at grain boundaries. The Nd-contained materials undergo a T6 heat treatment with a solution treatment at 530ºC for 8 hours followed by an aging at 250ºC for 12 hours. The heat treatment results in the Nd fully dissolved and then re-precipitated as Mg12Nd, distributing as cluster within the grains and along the grain boundaries. These Mg12Nd precipitation significantly increases the mechanical properties of the materials, especially the high temperature properties. The 200ºC tensile strength is 120 MPa for 0.2% Nd-contained alloy and 200 MPa at 2.6% Nd. Even at a higher temperature, 300ºC, the Nd-contained alloys still retain significant strength, 60MPa for 0.2% Nd alloy and 110 MPa for 2.6% Nd alloy. The heat treatment also results in some grain coarsening, and Nd acts as effective barriers for the grain agglomeration