Microstructure and Fatigue Behaviors of Dissimilar A6061/Galvannealed Steel Joints Fabricated by Friction Stir Spot Welding

Abstract

The microstructures, tensile shear properties, and tensile shear fatigue properties of dissimilar A6061/Galvannealed steel joints fabricated by friction stir spot welding (FSSW) were investigated. Fe4Al13 phases form as the intermetallic compound (IMC) layer at the joint interface between the A6061 matrix and the galvannealed layer consisting of FeZn7, Fe, and Zn. At the edge of the joint, the stirred layer in which the A6061 matrix and the galvannealed layer are stirred also forms. Moreover, the solidified part of the residual melt discharged from the joint area forms at the outer peripheries of the joint. In this study, FSSW was conducted for two total welding durations: 9 and 10 s. Although the thickness of the remaining A6061 sheet in the welded area decreased with an increase in the welding time, the effects of the total welding time on tensile shear and tensile shear fatigue properties were negligible. A fatigue fracture occurred in the A6061 matrix and at the joint interface at the high cycle fatigue region and the low cycle fatigue region, respectively. In the case of the interfacial fracture, the crack was generated in the solidified part of the residual melt or at the interface between the solidified part and the stirred layer.

Microstructures at the Interface of Al alloy and galvannealed steel jointed by scrubbing refill friction stir spot welding

“…The composition of the IMC layer was close to that of FeAl6. When the GA steel sheet and Al alloy sheet were joined by FSSW, Fe4Al13 was frequently observed at the interface 6) . The present experiment shows FeAl6 also formed in the region produced under the pin of Sc-RFSSW.…”

Phase Formation during Heating of Amorphous Nickel-Based BNi-3 for Joining of Dissimilar Cobalt-Based Superalloys

“…Also, depletion of chromium in adjacent zones through the consumption of secondary phase precipitations reduces corrosion resistance, particularly at high temperatures. Consuming alloying elements of base metals in area adjacent to the bonding zone reduces the alloying elements, leading to reinforcement with a solid solution and carbide deposition (such as tungsten, molybdenum, and chromium) [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58]. Consequently, it is essential to apply post-bond heat treatment to remove secondary phase compounds in the diffusion-affected zones.…”

Microstructure and Mechanical Properties of A6061/GA980 Resistance Spot Weld

“…Therefore, the realization of a hybrid structure of steel and a Al-alloy for car bodies is attracting attention. Thus dissimilar bonding with the Al-alloy and steel has been investigated [3][4][5][6]. In the welding of structural element of the car body, resistance spot welding is used due to low thermal deformation and short time welding.…”