Investigation into the Effect of RFSSW Parameters on Tensile Shear Fracture Load of 7075-T6 Alclad Aluminium Alloy Joints

Abstract

The aim of the investigations was to determine the effect of parameters of refill friction stir spot welding (RFSSW) on the fracture load and failure mechanisms of the resulting joint. RFSSW joints were made in 7075-T6 Alclad aluminium alloy sheets using different welding parameters. The load capacity of joints was determined under tensile/shear loadings. Finite element-based numerical simulations of the joint-loading process were carried out, taking into account the variability of elasto-plastic properties of weld material through the joint cross-section. The influence of welding parameters on selected phenomena occurring during the destruction of the joint is presented. The considerations were supported by a fractographic analysis based on SEM images of fractures. It was found that there is a certain optimal amount of heat generated, which is necessary to produce the correct joint in terms of its load capacity. This value should not be exceeded, because it leads to weakening of the base material and thus to a reduction in the strength of the joint. Samples subjected to uniaxial tensile shear load showed three types of failure mode (tensile fracture, shear fracture, plug type fracture) depending on the tool rotational speed and duration of welding. Prediction of the fracture mode using FE-based numerical modelling was consistent with the experimental results. The samples that were damaged due to the tensile fracture of the lower sheet revealed a load capacity (LC) of 5.76 KN. The average value of LC for the shear fracture failure mechanism was 5.24 kN. The average value of the LC for plug-type fracture mode was 5.02 kN. It was found that there is an optimal amount of heat generated, which is necessary to produce the correct joint in terms of its LC. Excessive overheating of the joint leads to a weakening of the base metal and thus a reduction in the strength of the joint. Measurements of residual stresses along the axis specimens showed the presence of stresses with a certain constant value for the welded area on the side of the 1.6 mm thick plate.

Mechanical properties and failure analysis of refill friction stir spot-welded 5052/2A12 joints

“…Figure 10 shows the distributions of von Mises equivalent strains in the two fracture modes in the cross-section. Similar to the numerical simulation results of Kubit et al [9], the main strain was mainly distributed at the lap interface and the upper-plate TMAZ/SZ interface (Figure 10(c,i)). However, owing to significant differences in properties of the upper and lower plates, only the upper plate incurred significant strain during the fracture process.…”

“…With the global shortage of resources and increasingly severe environmental problems, lightweight materials such as aluminium alloys are widely used in the manufacturing of structural components for aerospace applications owing to their excellent properties that assist with weight reduction [1][2][3]. Methods that can be used to spot-weld aluminium alloys include resistance spotwelding (RSW) [4], laser spot-welding (LSW) [5], friction stir spot-welding (FSSW) [6,7], riveting [8], and refill friction stir spot-welding (RFSSW) [9]. Fabrication of lap joints of dissimilar aluminium structural components with unequal thickness, such as joining of a handle of 5xxx Al to a plane skin of 2xxx Al, generally proceeds using a joining technique.…”

The Effect of RFSSW Parameters on Load Capacity of EN AW-6082-T6 Aluminium Alloy and AlCu Bimetallic Joints

“…The RFSSW welding tool consists of three components [26]: a pin with diameter of 5.2 mm, a sleeve with an external diameter of 9 mm and a clamping ring. The detailed procedure of the re ll friction stir spot welding process can be found in previous papers by the authors [23,26]. In general, the welding procedure consists of four steps touchdown, plunging, re lling and tool retraction.…”

“…It was found that hook height and joint integrity are the key parameters in uencing load capacity of the joints. RFSSW is commonly used to join various grades of aluminium alloys used in the aerospace and automotive industries [23,24]. Takeoka et al [25] developed scrubbing RFSSW (sc-RFSSW) to join non-coated mild steel and aluminium alloy.…”

Effective Range of FSSW Parameters for High Load-Carrying Capacity of Dissimilar Steel A283M-C/Brass CuZn40 Joints

“…In 1991, friction stir welding (FSW) was initially introduced by TWI in the United Kingdom as a newly developed solid-state welding process, particularly for joining aluminum alloys with specific requirements that should be fulfilled [1,2]. Then friction stir spot welding (FSSW) was developed as one of its variant for local joining of similar and dissimilar sheets [3][4][5][6][7][8][9] as a promising technique with similarities to the basic concepts of linear FSW with a specific requirement where no lateral movement of the tool is required [10]. More interestingly, the rotating tool pierces the sheets that are being welded and then produces a stir zone.…”