Composition and stability of Al2(Mg,Ca) compound in alloys of Al – Mg – Ca – (Zn) system

Alloys based on the Al – Mg – Ca – (Zn) system may be attractive as a class of low-density aluminum alloys combining strength, technological effectiveness and lightness. With a minimum proportion of zinc, magnesium plays the main role in strengthening, which should be maximally included in the composition of an aluminum (Al)-based solid solution. Therefore, compounds that pull magnesium from (Al) can lead to a decrease in the strength of the alloy. Such a compound is the phase described by the formula Al2(Mg,Ca) and previously undetectable in alloys of the Al – Mg – Ca – (Zn) system. The aim of the work was to determine the magnesium concentrations at which this compound was detected, to study its stoichiometric composition, stability during heat treatment and to determine the temperature range of its formation. The solution of these problems was implemented using optical (OM) and scanning microscopy (SEM) techniques, thermal analysis and the CALPHAD computational approach. Al2(Mg,Ca) was determined to be present in alloys containing 3–6% magnesium and 4% calcium, and changes its stoichiometric composition inversely depending on the magnesium content: with the decrease of magnesium, its share in the compound increases. The classical heat treatment for magnals has no effect on the chemical composition of the phase, and it remains stable. A temperature range was identified in the Al4%Mg8%Ca alloy when the formation of the compound of interest was detected. The alleged nature of its occurrence is described by the eutectic reaction L → (Al) + Al2(Mg,Ca). At the same time, the actual data of the thermal analysis have good convergence with the calculated values. The research was carried out at the expense of the grant of the Russian Science Foundation No. 23-79-01055 (optical and scanning microscopy, thermal analysis) and the funds of the P.L. Kapitsa grant of the Moscow Polytechnic University, implemented within the framework of the Priority 2030 program (melting and casting, heat treatment).