Characterization of Fe-Rich Intermetallic Phases in a 6xxx Series Al Alloy

Intermetallic phases formed during directional Bridgman solidification of a 6xxx series Al alloy in the growth velocity range 5-120 mm/min have been characterised using conventional and high-resolution transmission electron microscopy. Cubic αc-AlFeSi and β-AlFeSi were always present in the alloy, but Al13Fe4 was only observed at 5mm/min and monoclinic αT-AlFeSi at 80 mm/min. Cubic αc-AlFeSi was observed to have a variety of morphologies resulting from flexibility in its growth mechanisms. β-AlFeSi with twins and faults showed strongly anisotropic growth by steps, resulting in its platelet morphology. Occasionally blocky β-AlFeSi particles were observed particularly at 30-60 mm/min, suggesting that other mechanisms could influence their morphology. Two types of composite particles, β-AlFeSi/Al13Fe4 and β-AlFeSi/cubic αc-AlFeSi, were observed in this alloy, and likely formed by two quasi-peritectic reactions.