Effect of Mn and cooling rates on α-, β- and δ-Al–Fe–Si intermetallic phase formation in a secondary Al–Si alloy

Abstract

Secondary Al–Si alloys Al7.1Si(1.5-xMn)Fe(xMn)Mn with xMn = 0, 0.3, 0.375, 0.6, 0.75 at.% have been solidified with different cooling rates: 0.05 K/s, 1.4 K/s, 11.4 K/s and 200 K/s. In the ternary alloy with xMn = 0 at.%, formation of the primary αh phase is suppressed upon higher cooling rates at the cost of formation of plate-shaped β and δ phase particles. In the quaternary alloys, with increasing Mn content, αc-phase particles with Chinese-script morphology form and replace the plate-shaped intermetallic particles. While the αc phase forms at intermediate cooling rates only, plate-shaped particles additionally form at low and high cooling rates. The β phase dominates after solidification with lower cooling rates and the δ phase dominates upon higher cooling rates in the plate-shaped particles. The kinetic effect in terms of solidification rate and the chemical composition effect on the phase selection of Fe-containing intermetallic particles in the alloys along the solidification path have been discussed.