The microstucture,mechanical properties and fracture behaviors of semi-continuous cast Mg-8Gd-3Y-0.5Zr(wt.%,GW83K) alloy after different heat treatments were investigated.Almost all the eutectic compounds were dissolved into the matrix and there was no evident grain growth after optimum solution treatment at 500 ℃for 4h.Further ageing at low temperatures led to significant precipitation hardening,which strengthened the alloy.Peak-aged at 200 ℃,the alloy had the highest ultimate tensile strength(UTS) and lowest elongation at 395 MPa and 2.8%,respectively.When aged at 225 ℃ for 15 h,the alloy exhibited prominent mechanical performance with UTS and elongation of 363 MPa and 5.8%,respectively.With regard to microstructure and tensile properties,the processes of 500 ℃,4h+225℃,15 h are selected as the optimal heat treatment conditions.The alloy under different conditions shows different fracture behaviors:in the as-cast alloy,a quasi-cleavage pattern is observed;after solution treatment,the alloy exhibits a trans-granular quasi-cleavage fracture;after being peak-aged at 200 ℃ and 225 ℃,the fracture mode is a mixed mode of trans-granular and intergranular fracture,in which the inter-granular mode is dominant in the alloy peak-aged at 200 ℃.
The sliding friction and wear behaviors of Mg-11Y-5Gd-2Zn-0.5Zr （wt%） alloy were investigated under oil lubricant condition by pin-on-disk configuration with a constant sliding distance of 1,000 m in the temperature range of 25-200℃. Results indicate that the volumetric wear rates and average friction coefficients decrease with the increase of sliding speeds, and increase with the increase of test temperature below 150℃. The hard and thermally stable Mg12（Y,Gd）Zn phase with long-period stacking order structure in the alloy presents significant wear resistance, The wear mechanism below 100℃ is abrasive wear as a result of plastic extrusion deformation. The corporate effects of severe abrasive, oxidative, and delaminating wear result in the tribological mechanism above 100℃.
