Refilling Probe Hole of Friction Spot Joints by Friction Forming

Abstract

Friction stir spot welding (FSSpW) is a variant of friction stir welding (FSW) that has wider industrial application. However, Probe hole left after the welding is the main limitation of their process. In this present study, modified FSSpW has been developed and the refilling is achieved by friction forming process. This process has been called Friction Stir Spot Welding with refilling by Friction Forming Process (FSSpW-FFP). The Aluminum alloy (AA 6061-T6) plates are welded in two stages. Welding and refilling are achieved in first and second stages, respectively. Mechanical and metallurgical properties of the joints are studied and compared with welds made by FSSpW. The mechanical properties studied in the present work are tensile shear strength and microhardness. Macro-and microstructures of weld joints are compared and analyzed. The mechanical and metallurgical properties of the joints made by FSSpW-FFP are found to be better than the joints made by FSSpW. The tensile shear strength of the joint with refilled hole is higher than that of the joint with probe hole. The refilling process increases effective cross-sectional area of the nugget, resulting in higher tensile shear strength and joint efficiency at medium and high tool rotational speeds. After experiment, fracture surfaces are analyzed in detail using scanning electron microscope (SEM). The pull out of the nugget, i.e., plug type fracture, occurs in the joint with refilled probe hole, while shear fracture through the nugget is observed in the joint with probe hole. IntroductionFriction stir spot welding with refilling by friction forming process (FSSpW-FFP) is achieved in two stages. In the first stage, a backing plate with hole is prepared. The hole-axis is matched with the tool axis. The metal plates to be welded are fixed on the backing plate, and the tool is lowered under rotation. The tool is withdrawn after a predetermined time. During the first stage, the metal gets extruded into the hole in the backing plate [ Figs. 2(a) and (b)]. In the second stage, the joint obtained is tilted 180 and fixed on the solid backing plate [Figs. 2(c) and (e)]. A friction forming tool is lowered to touch the joint under rotation. During this stage, refilling of the probe-hole occurs through desired downward metal flow of extruded material on the surface of the plate made of ductile materials using a friction forming tool.Recently, lightweight metals such as aluminum alloys and magnesium alloys are increasingly used, especially in the automotive and aerospace industry, in which weight saving is extremely important. Resistance spot welding (RSW) has been widely used for decades in the automotive and other industries for fabricating sheet metal assemblies. However, the conventional RSW technique is unsuitable for joining lightweight metals because of its demerits such as high operating and investment cost due to high thermal and electrical conductivity of lightweight metals, consumption of RSW probe during joining, large heat distortion, and poor weld strength in jo...

Microstructure and failure mechanisms of refill friction stir spot welded 7075-T6 aluminum alloy joints

“…This phenomenon can be attributed to rotation of the nugget, which is schematically shown in Fig. 11, the rotation of nugget gives rise to the generation of the load component perpendicular to the loading direction and in turn causes the crack to grow to the thickness direction [4,7]. Fig.…”

“…Recently, aluminum alloys are used widely, especially in the automobile and aerospace industry, in which weight saving is extraordinarily important [2,4,5]. Resistance spot welding (RSW) and riveting are the primary methods used today for single point joining.…”

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

“…Prakash and Muthukumaran [49] investigated refill FSSW of Al-Mg-Si aluminum, in the study, joint that had higher strength than the joint made by conversational FSSW because refilling process increased effective cross-sectional area of the nugget. Uematsu et al [20] also reported that refilling process improved tensile strength by about 30%.…”

An experimental investigation on the dissimilar joining of AA6061 and 1Cr18Ni9Ti by refill friction stir spot welding and its mechanical properties

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