Dissimilar friction stir spot welding of low carbon steel and Al–Mg alloy by formation of IMCs

Abstract

Dissimilar lap joints of low carbon steel and Al-Mg alloy were obtained by friction stir spot welding. Mechanically mixed layer between top and bottom plates was not formed at the weld nugget due to the limited tool penetration and the pin height of welding tool lower than the thickness of Al plate laid in top side. These welding conditions made it possible to weld steel plate using welding tools made out of a general tool steel. With increasing tool penetration depth (TPD), tensile shear force of joint increased and maximum value of 3?0 kN was obtained at the TPD of 0?5 mm, but excessive tool penetration beyond 0?5 mm was caused in a deformation of Al plate of top side. In the result of interface observation, interaction layer was formed between Fe and Al alloy, which was constituted by various intermetallic compounds (IMCs). Consequently, the size of strongly bonded area containing Fe 3 Al and Fe 4 Al 13 IMCs increased with TPD, which resulted in the increase in joint strength under the limited TPD.

Microstructure and Mechanical Properties of Al/Steel Friction Stir Lap Weld

“…Movahedi et al [19] found that IMC layer with a thickness of less than 2 µm will not degrade joint quality. Similar results were suggested by Lee et al [20] and they reported that 2 µm IMC layers with the composition of Fe 3 Al, Fe 4 Al 13 could contribute to the joint strength. Chen et al [21] used Zn coating on the steel surface to improve the weldability of Al and steel by means of promoting the formation of Al-Zn low melting point eutectic structure.…”

“…Researchers have also studied Al/steel friction stir lap welding (FSLW) joint [18][19][20][21][22]. Kimapong and Watanabe [18] carried out that the maximum shear load of FSLW joint of 5083 aluminum alloy and SS400 mild steel could reach about 77% of aluminum alloy base metal.…”

Microstructural evolution during friction stir welding of dissimilar aluminum alloy to advanced high-strength steel

“…The local melting of aluminum was reported, and sheared-off steel platelets encompassed with IMC layers of Fe 4 Al 13 and Fe 2 Al 5 was observed in the weld nugget. Lee et al [14] did experiments on friction stir lap joint between Al 5083 and St-12 mild steel and reported that 2-μm IMC layers with the composition of Fe 3 Al, Fe 4 Al 13 can actually contribute to the joint strength. This statement was further verified by Movahedi et al [5], and they reported that intermetallic compound layer with a thickness of less than 2 μm will not degrade joint quality.…”

Modelling and visualisation of material flow in friction stir spot welding

“…Studies of FSSW, such as Bozzi et al (2010) and Lee et al (2009), have largely focussed on microstructural and property characterisation, including the formation of intermetallic reaction layers at the weld interface in aluminium-steel joints. In contrast, while investigations by Uematsu et al (2010) and Coelho et al (2008) have explored the influence of the material flow behaviour on weld formation, their limited direct observation make interpretation difficult.…”