Magnesium Solubility in Primary α-Al and Heat Treatment Response of Cast Al-7Si-Mg

• Main Authors: Jorge Santos, Arne K. Dahle, Anders E. W. Jarfors
• Format: Article
• Language: English
• Published: MDPI AG 2020-05-01
• Series: Metals
• Subjects: aluminium alloys; solid-solution; heat treatment; solubility; rheocasting; mechanical properties
• Online Access: https://www.mdpi.com/2075-4701/10/5/614

Magnesium and silicon concentrations in the interior of primary α-Al of Al-7Si-Mg alloys were studied at temperatures in the liquid-solid range and just after solidification was completed. Analysis of the results showed that the magnesium concentration in the interior of primary α-Al is very low in the temperatures range from the liquidus to the start of the Al-Si eutectic reaction. Formation of silicon-rich phases during eutectic reactions, such as eutectic silicon and β-Al₅FeSi, phases trigger a significant increase in the magnesium concentration in the interior of primary α-Al, when sufficient time is allowed for solid-state diffusion to occur. When fast cooling rates are applied during the Al-Si eutectic reaction, most of the magnesium is retained in π-Al₈FeMg₃Si₆ and Mg₂Si phases formed during solidification. Semi-solid Al-7Si-Mg castings were produced with varying magnesium contents, and the mechanical properties were evaluated in the as-cast, T5 and T6 conditions. It was found that the 0.2% offset yield strength of the semi-solid Al-7Si-Mg castings in the T5 and T6 conditions increases linearly with the square root of the magnesium concentration in the interior of the α-Al globules formed during the slurry preparation process.