The effect of vanadium and grain refiner additions on the nucleation of secondary phases in 1xxx Al alloys

High purity Al-0.3 wt% Fe-0.1 wt% Si alloys with different Si, V and grain refiner contents were melt spun to produce microstructures of submicron secondary phases entrained in a higher melting point Al matrix. On reheating, a dispersion of eutectic liquid droplets forms that represents an exaggerated version of the liquid puddles that solidify pinched-off between Al dendrite arms during conventional casting. The subsequent resolidification of the droplets, analysed using differential scanning calorimetry (DSC), allows the nucleation-controlled aspects of secondary phase selection to be studied. The droplets solidify as the metastable FeAlm, phase in ribbons containing similar or equal to 500 ppm V or similar or equal to 100 ppm V plus Al-Ti-B, AI-Ti-C or Al-B grain refiner. This phase contributes to the "fir-tree" surface defect in commercial sheet products. This work suggests that the combination of V and Al-Ti-B promotes FeAlm, in commercial ingots, and confirms that solidification rate and bulk Si content also influence phase content. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.