Comparative study of fatigue behaviour in dissimilar Al alloy/steel and Mg alloy/steel friction stir spot welds fabricated by scroll grooved tool without probe

Abstract

Aluminium alloy A6061-T6 or magnesium alloy AZ31 sheet was welded to steel sheet by a friction stir spot welding technique using a scroll grooved tool without a probe. The material flow in the nugget of the Mg/steel weld was less than that in the Al/steel one. The Al/steel weld exhibited higher static tensile-shear strength than the Al/Al weld, while the strengths of Mg/steel and Mg/Mg welds were comparable. Tensile-shear fatigue tests were performed using lap shear specimens of both dissimilar and similar welds. The dissimilar welds exhibited nearly the same fatigue strengths as the similar ones. The effective nugget size in the dissimilar welds was defined as the area where Al or Mg alloy remained on the steel side after static fracture. When the fatigue strengths of dissimilar welds were evaluated based on the effective nugget size, the normalised fatigue strengths of Al/steel and Mg/steel welds were comparable.

Friction Stir Spot Welding: A Review on Joint Macro- and Microstructure, Property, and Process Modelling

“…In the similar welds, fracture mode was irrelevant to load levels for lap-shear specimens, and crack took place in lower sheet under high or low load levels [55,56]. However, the fatigue modes of FSSW in AZ31 depended on the cyclic load amplitude [53,57]. Nugget pullout took place under high load amplitude, while crack propagated along width of samples under low load amplitude [53].…”

“…Tran et al [59] investigated that failure mode of the 5754-7075 welds in lapshear specimens, under quasistatic loading conditions, crack propagated along the nugget circumference, under cyclic loading conditions, crack propagated in the width direction of the specimen, and the left part of the lower sheet was eventually separated (Figure 10 [61]. The fatigue cracks between Al-steel and Mg-steel welds grew through the interface dominantly [57]. The results were similar to the results of Mg-Al in [61].…”

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

“…One of the typical desired pairs is aluminum alloy and advanced high-strength steel. Successful and reliable joints between these two materials are hardly achievable using traditional fusion welding techniques due to their great differences in physical and mechanical properties as well as the formation of the large amount of brittle intermetallic compounds (IMCs) [2][3][4][5][6], which aggravates crack initiation and significantly deteriorates joint.…”

Experimental Investigation on Joining Dissimilar Aluminum Alloy 6061 to TRIP 780/800 Steel Through Friction Stir Welding

“…One of these typical pairs of materials is aluminum alloy and steel, which are highly difficult to be welded together due to their great differences in physical and mechanical properties. Moreover, the large amount of brittle IMCs formed during traditional fusion welding process will severely deteriorate the joint and initiate a fast rupture under applied stress [2][3][4][5][6].…”