Mechanical performance of AA6181 refill friction spot welds under Lap shear tensile loading

Abstract

A B S T R A C T This study investigates the fracture behaviour of refill friction spot welding welds under shear tensile loading. Overlap joints of 6181-T4 aluminium were produced in 1.7-mm sheets by varying the rotational speed from 1900 to 2900 rpm and the welding time from 2 to 3.4 s while keeping the plunge depth constant at 1.75 mm. After shear tensile tests, the samples were analysed using optical microscopy and scanning electron microscopy. The strength of the weld and its ductile/brittle behaviour are associated with the nucleation, growth and propagation of two types of cracks: circumferential cracks and annular cracks. Welds produced with longer welding times (≥3 s) and slower rotational speeds (1900 rpm) had higher strengths, low scattering and high energy absorption prior to failure, while welds produced with short welding times (2 to 2.4 s) resulted in poor joints, especially when they also used high rotational speeds.

Fatigue assessment of refill friction stir spot weld in AA 2024‐T3 similar joints

“…Thermomechanical affected zone is the most likely site for a crack nucleation and propagation because this zone presents lower hardness, elongated grains, hook, and a high stress level. In addition, the eccentricity of the load line between the upper and lower plates promotes secondary bending, which generates a triaxial stress state and can lead to crack initiation and propagation by either TW or PPO …”

“…In the case of a quasi‐static lap shear test of refill FSSW, the crack initiates at the hook tip in high‐quality spot welds and propagates circumferentially to the spot weld . The dimensions of the curved hook intensify the stress state, influence the lap shear strength, and reduce the joint integrity.…”

“…Although refill FSSW has shown to produce excellent performance under shear loading, a few fatigue life studies have been reported. Effertz et al analysed the fatigue life in similar welds of AA7050‐T76.…”

“…[13][14][15] For this purpose, the Weibull distribution has been applied to assess fatigue results statistically and the shape parameter and confidence are calculated through simple application to a set of samples. 14,16,17 Although refill FSSW has shown to produce excellent performance under shear loading, [2][3][4]18 a few fatigue life studies have been reported. Effertz et al 19 analysed the fatigue life in similar welds of AA7050-T76.…”

Metallographic evaluation of the weldability of high strength aluminium alloys using friction spot welding

“…It differs from the friction stir spot weld (FSSW) process in the ability to refill the keyhole and hence eliminates its major disadvantages: stress concentration and corrosion at the keyhole. Friction spot welding is seen as a green manufacturing method because no additional filler material is required and there is no waste material [4,7]. The welding process has potential for mass production lines as the welding time is relatively short and the process can be automated easily.…”