Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

abstract Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformationinduced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) tech-nique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetalliccompound (IMC) layer of FeAl or Fe 3 Al with thickness of less than 1 l m was formed at the Al–Fe interfacein the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning elec-tron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix com-posite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetalliclayer orsimply intermetallic particles. Effects of process parameters on the joint microstructure evolutionwere analyzed based on mechanical welding force and temperature that have been measured during thewelding process. 2014 Elsevier Ltd. All rights reserved. 1. IntroductionGrowing concerns on energy saving and environmental preser-vations increase the demand for lightweight vehicles. Considerablevolumes of advanced high strength steel sheet have been appliedinto automotive parts in order to reach the objective of bothweight reduction and crashworthiness enhancement. However,further weight reduction of 30% or more is hardly achievable withexclusive dependence on the use of thinner steel sheets. Multi-material vehicle structures is an efficient countermeasure againstthis problem [1], which necessitates the development of reliableand cost-effective dissimilar material joining technique. One ofthe desired pairs is aluminum alloy and advanced high strengthsteel, which is highly difficult to be welded together due to theirdifferences in physical and mechanical properties as well as theformation of large amount of brittle intermetallic compounds(IMC) using traditional fusion welding techniques [2–6].Friction stir welding (FSW), which was first developed by TheWelding Institute (TWI) in 1991 [7], has a solid-state nature andtherefore exhibits certain advantages over traditional fusion weld-ing methods. First, it can significantly avoid solidification relatedproblems, such as oxidization, shrinkage, porosity, and hydrogensolubility [8]. Second, the associated low heat input can effectivelyinhibit intermetallic compound (IMC) layer formation, whichmakes it a promising solution for dissimilar material joining. Sev-eral studies have been carried out on FSW of aluminum alloy tosteel sheets. Uzun et al. [9] reported the joint strength between304 stainless steel and Al 6013-T4 with thickness of 4 mm canreach approximately 70% of the base aluminum alloy. Ghoshet al. [10] did FSW of pure Al to 304 stainless steel and the ultimatetensile strength can achieve 82% of Al. Presence of Fe