A Calorimetric Evaluation of the Role of Impurities in the Nucleation of Secondary Phases in 1xxx Al Alloys

Superpurity (> 99.995wt% pure) lxxx series Al-0.3wt%Fe-0.lwt% Si alloys with different impurity additions have been melt spun to produce ribbons with microstructures of fine scale ∼0.1-0.2μm diameter secondary phase particles entrained in a higher melting point Al matrix. The melting and resolidification behaviour at 2Kmin -1 of the secondary phase particles while entrained in the solid matrix was monitored using differential scanning calorimetry, to simulate the nucleation of secondary phases in liquid interdendritic regions during the final stages of solidification in casting. The melting and resolidification behaviour of 500ppm V and Zr doped superpurity ribbons is the same as that of a commercial purity ribbon. This indicates that V is responsible for the promotion of the metastable FeAl m phase in the commercial purity ribbon. The presence of FeAl m in direct chill (DC) cast commercial purity alloys indicates that V also influences phase selection in the faster cooled (∼5-10Ks -1 ) regions of these alloys.