Effect of Cu addition on mechanical properties of Mg-Gd-Zn-Zr casting alloy

Mg-Gd-Zn-Cu-Zr cast alloys were developed for high strength casting products. Effects of Cu addition on microstructures and tensile properties of these alloys were investigated. Depending on Cu content different compound phases existed at grain boundaries in cast sample after solution treatment. In low Cu content alloys, these phases were identified as mainly Mg 5Gd with minor amount of LPSO phase. In other alloys, the LPSO phase forms principally along with Mg 12 (Cu, Zn) Gd. The type of its phase was 14H-type structure in all fabricated alloys. In addition, age-hardening occurred around 473 K after solution treatment. T6-treated alloys including the LPSO phase predominantly exhibited excellent ductility and work hardening. Mg-3.2Gd-1.0Cu-0.5Zn-0.2Zr (mol%) alloy, in which volume fraction of the LPSO phase was about 45%, indicating ultimate tensile strength of 370 MPa and elongation to failure of 10%. On the other hand, low Cu content alloys with few LPSO phase showed lower tensile strength due to scarce elongation regardless of remarkable age-hardness. Eventually, the LPSO phase increased ductility and tensile strength. © 2012 The Japan Institute of Light Metals.