Abstract
Sodium is an undesired impurity element in aluminum-magnesium alloys. Despite its trace amount, it leads to high temperature embrittlement (HTE) due to intergranular fracture which is prone to edge cracking during hot rolling. In the present work, thermodynamic investigation is carried out to elucidate its mechanism through revealing the correlations between HTE, phase formation, temperature, and composition in Al-Mg alloys. It is found: (i) HTE is ascribed to the formation of the intergranular Na-rich liquid phase which significantly weakens the strength of grain boundaries; (ii) for a given Mg content, there exists a maximum Na content above which HTE cannot be avoided; and (iii) for a given alloy, a proper hot-rolling temperature should be chosen with respect to Na and Mg contents in order to suppress HTE. The HTE sensitive zone and a hot-rolling safe zone of the Al-Mg-Na alloys are defined as functions of processing temperature and alloy composition. The tendency of HTE formation is evaluated based on thermodynamic simulations of phase fraction of the intergranular Na-rich liquid phase. The present work provides fundamental understanding of Na-induced HTE in Al-Mg alloys and contributes to the processing control of Al-Mg alloys.