Quench Sensitivity and Phase Transformation Kinetics of AlSi7MnMg High Pressure Vacuum Die Casting

Abstract

The quench sensitivity of an AlSi7MnMg alloy in high-pressure vacuum die (HPVD) casting was investigated by time-temperature-transformation and time-temperature-property diagrams with an interrupted quench technique. The quench sensitive temperature range of the alloy is from 260 to 430 °C and its nose temperature is 350 °C. The mechanical strength versus cooling rates of the HPVD casting was predicted using quench factor analysis method and verified by experimental results. The critical cooling rate is 6 °C/s to remain 95% of the maximal mechanical strength. The coefficients k2 - k5, related to the nucleation and precipitation kinetics of TTP curves, and phase transformation diagrams were determined. The precipitation of Mg2Si phase in the castings was observed during isothermal treatment using transmission electron microscope. Moreover, the quench sensitivity and kinetics of the phase transformation of AlSi7MnMg alloy and AlSi10MnMg alloys were compared. It reveals that the quench sensitivity and phase transformation rate of the former are lower than that of the latter.