Strengthening Effects of Zn Addition on an Ultrahigh Ductility Mg-Gd-Zr Magnesium Alloy.

A newly developed Mg-2Gd-0.5Zr-Zn ( = 0.5, 1.0, 2.0, 3.0 wt %) alloy system exhibits significant strengthening by doping with Zn. In order to understand the strengthening mechanism, the microstructure, texture evolution, and mechanical properties of ultrahigh ductility Mg-2Gd-0.5Zr alloys with a Zn addition were systematically investigated. The addition of Zn results in the formation of Mg-Gd-Zn intermetallic compounds along grain boundaries, which encourages grain refinement during hot extrusion via the particle stimulated nucleation (PSN) mechanism. Furthermore, during texture sharpening the pole changes from <20 2 ¯ 1> to <01 1 ¯ 0>, which also occurred in the extruded alloys with Zn addition, which is unfavorable for the basal slip and tensile twinning. Mg-2Gd-0.5Zr-3Zn shows well-balanced strength and ductility with a tensile yield strength (YS) and ultimate tensile strength (UTS) of 285 and 314 MPa, accompanied by a high tensile elongation of 24%. They are superior to those of commercial AZ31. The enhanced strength is attributed to grain refinement, precipitation strengthening, and texture sharpening induced by alloying with Zn. The research result is also of great value to the development of low rare-earth, high strength, and high room temperature ductility magnesium alloy.