On the role of zinc on the formation and growth of intermetallic phases during interdiffusion between steel and aluminium alloys

The effect of Zn - both within Al and as a coating on steel - on the intermetallic phase formation and growth was systematically studied in controlled experiments, simulating the interfacial reactions taking place in dissimilar solid/solid and solid/liquid joining procedures. Independent from the reaction temperature, the addition of 1.05 at.% Zn (2.5 wt.%) to Al had no effect on the reaction layers' build-up with the eta phase (Al5Fe2) as the dominant component, but accelerated their parabolic growth up to a factor of 13. While Zn-coatings on steel were found to be beneficial for the regular and even formation of intermetallic reaction zones in solid/liquid joining procedures, their role in solid-state processes was found to be more complex and, if no countermeasures are taken, extremely detrimental to the joint properties. Possible reasons for the Zn-induced growth acceleration are discussed, as well as consequences for possible optimisation steps for reducing harmful effects of Zn in dissimilar joints between Al alloys and steel. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.