Characterization of Intermetallic Compounds in Dissimilar Material Resistance Spot Welded Joint of High Strength Steel and Aluminum Alloy

Abstract

Dissimilar materials of H220 Zn-coated high strength steel and 6008 aluminum alloy were welded by median frequency resistance spot welding. Interfacial characteristics and kinetics of growth of intermetallic compound layer at steel/aluminum interface in the welded joint were investigated. The intermetallic compound layer was mainly made up of η-Fe2Al5 and θ-FeAl3 phases, and its morphology and thickness varied with positions along the interface. The growth behavior of the intermetallic compound layer was dominated by η-Fe2Al5, which exhibited parabolic characteristic. The growth coefficient of η-Fe2Al5 could be expressed as with k0 of 132 m 2 /s and Q of 239 kJ/mol. The kinetics of growth of the intermetallic compound layer indicated that its formation and growth were mainly driven by reactive diffusion between Fe and Al atoms, and hence the thickness and morphology of the layer were dependant on interaction time between liquid aluminum alloy and solid steel, and also interfacial temperature history during welding. The brittle intermetallic compound layer at the steel/aluminum interface was the weak zone where cracks inclined to derive and propagate during tensile shear testing. The fracture surfaces of the welded joint displayed mixed fracture morphology with both brittle and ductile features.

Microstructure and Wear Behavior of Cermet/Iron Alloy Cladding Layers on A6061 Alloy Coated by Resistance Seam Welding Method

“…When the surface of the A6061 alloy melted and started to contact with SHA powders in the welding process, Fe from SHA powders diffused into molten A6061 to form the Al-rich phase such as Fe 2 Al 5 and FeAl 3 because the diffusion coefficient of iron into aluminum is much greater than that of aluminum into iron [17]. Furthermore, according to the thermodynamic principles, the standard Gibbs free energy to form Fe 2 Al 5 is higher than FeAl 3 [18], so the formation of FeAl 3 was prior to the formation of Fe 2 Al 5 . In other words, the precipitations in the cladding layer could be considered to be FeAl 3 and the bulk and needle-like structure of FeAl 3 were also in agreement with previous works [19,20].…”

Resistance Spot Welding between Steel and Aluminum Alloy

“…Therefore, the resistance spot welding of aluminum alloy has been widely investigated recently. However, the resistance spot welding between the two kinds of materials accompanies some difficulties, because of the large difference in physical and thermal properties between aluminum alloy and steel, and the formation of brittle reaction products at the welding interface [1][2][3] . Hence, solid state welding methods have been studied in the last few years to acquire a sound joint, such as explosion welding [4] , diffusion welding [5] , friction stir welding [6] .…”

Structure of Iron-Based Cladding Layer on Al-Mg-Si Alloy Coated by a Resistance Seam Welding Method

“…Because the growth coefficient of Fe 2 Al 5 was larger than the FeAl 3 , 25) the FeAl 3 disappeared once the Fe 2 Al 5 nucleation was formed as shown in Fig. 7(c).…”

“…7(b)). 25) And then, FeAl 3 began to grow, because the diffusion coefficient of the iron into aluminum is much greater than that of the aluminum into iron, 26) and the Al atomic concentration near the SHA powder side was decreased. Therefore, the nucleation of Fe 2 Al 5 was formed at the expense of FeAl 3 .…”