Thermodynamics Study on the Precipitation of Mg₃₂(Al,Cu)₄₉ 　Intermetallic Compounds in Molten Al-Mg Alloy

Abstract

Recycling Al scraps is extremely important to achieve carbon neutrality. To produce wrought Al alloy, alloying elements must be controlled to a low concentration. However, Al scraps recovered from the society contain Cu, which is difficult to remove once dissolved in molten Al alloy. Fe, Si, and Mn can be removed from molten Al through the precipitation of intermetallic compounds by adding Mg. In this study, this method was applied to remove Cu from molten Al. Molten Al-Mg-10mass%Cu alloy was equilibrated with Mg₃₂(Al,Cu)₄₉ at 723 and 733 K, and Cu content of molten Al-Mg alloy was investigated. It was found that Mg₃₂(Al,Cu)₄₉ precipitated in molten Al-Mg-Cu alloy and the Cu content of molten Al-Mg alloy decreased from the initial content. The residual Cu content was higher at higher Mg content and lower temperature. The Cu removal from molten Al-Mg alloy through the precipitation of Mg₃₂(Al,Cu)₄₉ was thermodynamically discussed. The results revealed that the activity coefficient of Cu decreased at higher Mg content due to the attractive interaction between Mg and Cu although Mg₃₂(Al,Cu)₄₉ become more stable. Therefore, Cu content of molten Al-Mg alloy can be decreased at higher Mg content.