Precipitate transformation of τ-AlMn phases to Al8Mn4Ca during solution heat treatment of CaO-added AZ31 alloys

초록

The precipitate transformation mechanism of Al8Mn4Ca and its effect on mechanical properties of CaO-added AZ31 were investigated. Microstructural characterization showed that precipitate transformation occurred by dissolution of the C15 (Al2Ca) phase during solution heat treatment. Then, dissolved Al and Ca solutes have formed segregation layer near metastable tau (Al11Mn14 and Al8Mn11) which leads phase transformation. Depending on different diffusion kinetics of Al and Ca solutes, formation of Al8Mn4Ca or gamma(2) (Al8Mn5) was determined by distribution of C15 near tau. To this end, complex layered particle structures were frequently found. The precipitate transformation affected mechanical properties of the alloy. Due to fragment behavior during phase transformation and irreversibility of Al8Mn4Ca, duration of solution heat treatment affects hardening behavior. Precise control over the solution heat treatment process is necessary to obtain optimal properties in Ca-bearing Mg-Al-Mn alloys because of the unique conditions required for the formation of Al8Mn4Ca.

키워드