Effect of semisolid microstructure on solidified phase content in 1xxx Al alloys

Melt-spun high purity Al-0.3 wt% Fe-0.1 wt% Si alloys, containing V and Al-5Ti-1B grain refiner, were melted at 2 K/min from 635 degreesC to different temperatures above the solidus in a differential scanning calorimeter (DSC). Quenched and slow cooled (at 2 M/min) microstructures were examined using scanning electron microscopy (SEM). Melting was observed in a hot-stage reflected light microscope. Al-Fe4Al13 melted first, forming cell boundary liquid films. Rapid coarsening occurred at <4 K above the solidus via motion of these boundaries. Intracellular liquid droplets formed at 4-6 K above the solidus. These droplets have been demonstrated to be sites of metastable Al-FeAlm formation in V and Al-5Ti-1B containing alloys on solidification. With increasing temperature the liquid cell boundaries thickened and consumed the droplets, until there were none left at 10 K above the solidus, when the microstructure was fully molten. Consequently Al-FeAlm only formed in V and Al-5Ti-1B containing alloys when solidified following melting to 4-10 K above the solidus. (C) 2001 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.