Effect of heat treatment on the microstructures and mechanical properties of the extruded Mg-11Gd-1Zn alloy

A ternary alloy with composition of Mg-11Gd-1Zn (mass fraction, %) was prepared by conventional casting and extrusion. The microstructure and aging behavior of the alloy prepared was investigated. The results showed that the as cast microstructure of the alloy consisted of the alpha-Mg matrix, (Mg,Zn) Gd-3 eutectic and a 14H long-period staking ordered (14H-LPSO) phase. After extrusion the (Mg,Zn)(3)Gd eutectic networks were destroyed and its broken particles were arranged in strips along the direction of extrusion, and the 14H-LPSO phase distributed between (Mg,Zn)(3)Gd strips. Solid solution treatment at high temperature above 500 degrees C caused the dissolution of (Mg,Zn)(3)Gd phase into the matrix and increase of the 14H-LPSO phase. Precipitation of beta' and beta(1) metastable phase occurred when the solution treated specimens were aged at temperature of 225 degrees C (T6 treatment) and the 14H-LPSO phase formed during prior solution treatment remained in the microstructure after aging. Aging conducted on the extruded alloy (T5 treatment) also caused the formation of both of beta' and beta(1) precipitates, however the volume fraction of 14H-LPSO phase in the T5 treated specimens was lower than that in specimens after T6 treatment. High tensile strength combined with good ductility was obtained from the alloy after T6-aging. Published by Elsevier B. V.