Effects of Mg content on microstructure and mechanical properties of Al-14.5Si-4.5Cu alloy

Chih Ting Wu, Sheng Long Lee, Meng Hsiung Hsieh, Jing Chie Lin

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This study elucidates how Mg content affects the microstructure and mechanical properties of Al-14.5Si-4.5Cu alloy by adding 0.45 and 0.90 wt pct Mg. Primary silicon, eutectic silicon, acicular β-Al5FeSi, Al2Cu, and Al5Cu2Mg8Si6 phases were observed under the as-cast condition in low-Mg alloy. In high-Mg alloy, a large proportion of the acicular β-Al5FeSi phase was converted to Chinese script Al8Mg3FeSi6 phase. Neither the acicular β-Al5FeSi phase nor the Chinese script Al8Mg3FeSi6 phase dissolved in the Al matrix during solution heat treatment. Tensile testing indicates that T6-treated high-Mg alloy containing the Chinese script Al8Mg 3FeSi6 phase is better than the T6-treated low-Mg alloy that contains the acicular β-Al5FeSi phase. The morphologies of Chinese script Al8Mg3FeSi6 and acicular β-Al5FeSi phases affect the tensile properties of Mg-containing Al-14.5Si-4.5Cu alloys. Additionally, high-Mg alloy contains a higher concentration of Mg solute atoms in the Al matrix than low-Mg alloy, and so the former contains more λ' precipitates (Al5Cu2Mg 8Si6) after T6-tempering treatment. The large amount of λ' that precipitates in T6-treated high-Mg alloy may also enhance its tensile strength. The ultimate tensile strength (UTS) and elongation of the high-Mg alloy are superior to those of the low-Mg alloy.

Original languageEnglish
Pages (from-to)751-757
Number of pages7
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Issue number3
StatePublished - Mar 2010


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