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Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science


The effects of solution treatment time and Si content and morphology on microstructures and mechanical properties of heat-treated Al-Si-Mg cast alloys were investigated systematically. Five alloys, with Si levels ranging from 1 to 13 pct, were tested in as-cast, T4, and T61 conditions. The eutectic Si was both unmodified and Sr-modified. Results show that the microstructures are affected significantly by alloy composition, eutectic Si morphology, and solution treatment time. Si content has significant effects on ultimate tensile strength (UTS), yield strength (YS), and elongation as well as a strong influence on solution treatment response. In T61 treatment with different solutionizing times, UTS and YS reach their maximum values in similar to 1 hour of solutionizing followed by a decrease, then a slight increase, and finally, a plateau close to the maximum level. Elongation of alloys with a high Si content, 7 pct and 13 pct, increases rapidly at solutionizing times of 1 to 2 hours then varies in a wide range, showing improvements in the 4 to 10 hours range. The data indicate that a solution treatment time of similar to 1 hour is sufficient to achieve maximum strength. The changes in mechanical properties were correlated to changes in microstructure evolution-Mg-Si precipitation, Si particle fragmentation, and microstructure homogenization. Empirical models uniquely relating Si content to UTS and YS are given for T61 heat-treated alloys.





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Copyright 2011, ASM International. This paper was published in Metallurgical and Materials Transactions B-Process Metallurgy and Materials Processing Science Vol. 42 Iss. 1 pp. 171-180 and is made available as an electronic reprint with the permission of, ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.