Effect of Sleeve Plunge Depth on Interface/Mechanical Characteristics in Refill Friction Stir Spot Welded Joint

Abstract

Refill friction stir spot welding was employed to produce 6061-T6 aluminum alloy joints with different sleeve plunge depths. The interface characteristics of joint-line remnant and hook are investigated by optical and scanning electron microscopy. The joint-line remnant consists of primary bonding region and secondary bonding region, and two types of hook can be identified as downward hook and upward hook. Tensile shear results demonstrate that joint-line remnant and hook make interaction effects on tensile shear properties. The optimal joint is achieved when sleeve plunge depth was 2.0 mm with the corresponding failure load of 8673.4 N. Three different types of fracture mode are exhibited in joints produced at different sleeve plunge depths, which are closely related with the morphology of interface characteristics.

The Influence of Tool Wear on the Mechanical Performance of AA6061-T6 Refill Friction Stir Spot Welds

“…From the figures, the hook shape that was observed for all three conditions was similar, resembling an S-shape. This behavior was expected, since the PD was kept constant during this study and, as demonstrated in the literature [ 51 ], PD is one of the main parameters in control of the hook formation and geometry. As demonstrated by Cao et al [ 42 ], this influence of the PD on the hook shape develops from the plunging stage of the shoulder, which pushes the softened material beneath it downward, squeezing the adjacent material upward.…”

“…The hook is formed due to the material flow that is promoted by the shoulder movement and its rotation during the process. According to Silva et al [ 50 ] and Sun et al [ 51 ], the observed fracture modes are often related to the shape and height of the hook. In other words, the mechanical performance of the spot is strongly related to the hook configuration.…”

Evaluation of quantitative ultrasonic C-scan testing for refill friction stir spot welding joints based on time-frequency analysis

“…3.1. Analysis of the RFSSW joint metallograph Figure 4(a) demonstrates a representative axial cross-sectional metallograph of the RFSSW specimen, in which zone A is the BMZ, zone B is the nugget, and zone C is the boundary zone including the heat-affected and thermomechanical affected zone [10][11][12]. 4(a) which is the metallographic measurement value of the joint's diameter, is determined to be 8.89 mm.…”

“…The tool system consisted of an 18 mm diameter clamping ring, a 9 mm diameter sleeve, and a 5 mm diameter pin. The main welding parameters are shown in table 2, and the RFSSW process is illustrated in figure 1 [9][10][11][12]. Figure 2 shows an actual photo of the RFSSW specimen.…”

“…It offers unique welding characteristics, including a small heat-affected zone, minimal welding deformation, and low welding residual stress, making it suitable for lap welding thin aluminum sheets [8,9]. As the RFSSW process is complex and influenced by numerous parameters that affect joint quality, evaluating the quality of RFSSW joints using nondestructive testing has become an interesting topic in the academic community [8][9][10][11][12]. In recent years, ultrasonic nondestructive testing methods have gained significant attention for evaluating joint quality due to their portability, reliability, safety, and other advantages [13][14][15][16][17].…”