Efects of diferent casting mould cooling rates on microstructure and properties of sand-cast Al-7.5Si-4Cu alloy

In this work, Al-7.5Si-4Cu alloy melt modified by Al-10Sr, RE and Al-5Ti-B master alloys was poured into multi-step moulds made from three moulding sands, including quartz, alumina and chromite, to investigate comparatively the effects of different cooling rates of the casting mould on the alloy's microstructures and mechanical properties. The results show that with an increase in wall thickness, the cooling rate decreases, the dendrite arm spacing(DAS) increases significantly and the mechanical properties decrease steadily. The elongation is more sensitive to the cooling rate than the tensile strength. No obvious trend of the effect of wall thickness on hardness of the alloy was found. When the cooling rate is at its greatest, the microstructures and mechanical properties are the best when using chromite sand. The improvement of the properties is mainly attributed to the decrease of the DAS, the grain refinement and the metamorphic effect. Each of the three has a strong impact on the microstructures. Furthermore, a series of fitting models was established based on the data of the DAS to predict the mechanical properties of the multivariate sand-cast Al-7.5Si-4Cu alloy,

热疲劳环境下多元Al-7.5Si-4Cu合金的裂纹萌生扩展

研究了多元Al-7.5Si-4Cu合金在不同热处理状态下的热疲劳性能。结果表明,与铸态试样和淬火+时效热处理试样相比,T6态试样的力学性能最好,微观组织均匀,热疲劳性能最优良。当热循环次数≥10 000时,T6状态与淬火+时效试样由于Si相和A12Cu相的出现降低了裂纹扩展速率,铸态试样由于A12Cu相复熔球的存在导致裂纹扩展速率急剧上升。