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The differences of the microstructure and mechanical property between metal mould and sand mould cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment.In the as-cast specimens,the microstructure is similar and composed of α-Mg solid solution and eutectic compound of α-Mg+ Mg24(Gd,Y) 5;whereas the grain size using metal mould and sand mould is 27 μm and 71 μm,respectively.The eutectic compound of metal mould cast alloy was completely dissolved after solution treated at 500℃ for 8 h,however it needs higher temperature(525 ℃) and longer time(12 h) to achieve the absolute dissolving under sand mould condition.In contrast to metal mould,the peak time of sand mould alloy aged at 225 ℃ and 250 ℃ of was advanced by 4 h and 6 h,respectively.The precipitation reaction sequence in sand mould cast Mg-10Gd-3Y-Zr alloy during isothermal ageing at 250 ℃ follows S.S.S.S.→β″(D019) →β’(cboc) →β1(fcc) →β(fcc) ,which is similar to that in the alloy cast using metal mould.
The differences of the microstructure and mechanical property between metal mold and sand mold cast Mg-10Gd-3Y-Zr alloy were investigated both under as-cast condition and after solution heat treatment. In the as-cast specimens, the microstructure is similar and composed of α-Mg solid solution and eutectic compound of α-Mg + Mg24 (Gd, Y) 5; the grain size using metal mold and sand mold is 27 μm and 71 μm, respectively. The eutectic compound of metal mold cast alloy was completely dissolved after solution treated at 500 ° C for 8 h, however it needs higher temperature (525 ° C) and longer time (12 h) to achieve the absolute dissolving under sand mold condition. contrast to metal mold, the peak time of sand mold alloy aged at 225 ° C and 250 ° C was advanced by 4 h and 6 h, respectively. The precipitation reaction sequence in sand mold cast Mg-10Gd-3Y-Zr alloy at isothermal aging at 250 ° C follows SSSS → β "(D019) → β ’(cboc) → β1 (fcc) → β (fcc), which is simila r to that in the alloy cast using metal mold.