Friction Stir Welding (FSW) has been paid more attention in recent years due to its efficiency in welding materials that are difficult to weld by conventional fusion welding methods. There are several parameters that affect FSW process, so it is important to understand the relationship between different process parameters to maximize the quality and strength of the joint. This paper proposed an alternative method to predict FSW parameters and make a decision using a modified version of the adaptive neuro-fuzzy inference system (ANFIS) integrated with harris hawks optimizer (HHO). HHO was used to search for optimal values of ANFIS parameters and to determine the optimal operating conditions of the FSW process. The shared effect of welding speed, tool rotational speed, and plunge force on the mechanical properties of welded aluminium plates was simulated. The proposed model, called ANFIS-HHO, was used to predict the mechanical properties of FSW Al plates in terms of ultimate tensile strength (UTS) as functions of welding speed, tool rotational speed, and plunge force. The adequacy of the model was tested; the predicted data were in good agreement with the experimental data. The tool rotational speed and the empirical force index (EFI) have a significant impact on the mechanical properties of the welded joints. ANFIS-HHO technique was found to be a powerful optimization tool for predicting FSW parameters to achieve high joint strength.

Modeling of friction stir welding process using adaptive neuro-fuzzy inference system integrated with harris hawks optimizer

Revealing joining mechanism in refill friction stir spot welding of AZ31 magnesium alloy to galvanized DP600 steel

To obtain profiles with sound weld seams, the effects of extrusion parameters and heat treatment on microstructures and mechanical properties of the weld seam were revealed. It was found that the high extrusion speed increases the mechanical properties and welding quality of the welding area. The micro-voids formed in low temperature and low extrusion speed could hinder the grains from growing through the welding interface during heat treatment, which caused weak bonding of the weld seam. Lots of strengthening phases precipitated during aging treatment, which leads to the disappearance of the softened welding area and the improvement of tensile strength. However, the fine grains of welding area translated to coarse grains quickly during solution treatment, and the precipitated phases coarsened and the precipitation free zone (PFZ) widened when the aging time is excessive, above reasons result in the layered fracture of welding area and poor elongation. Tensile strength and elongation were improved simultaneously because of the fine grain boundary precipitates, narrow PFZ and fine homogeneous T1 phases formed in under-aged (UA) treatment. The weld seam obtained by high extrusion speed shows a fine combination of ultimate tensile strength (UTS) and elongation after UA treatment.

Effects of extrusion parameters and post-heat treatments on microstructures and mechanical properties of extrusion weld seams in 2195 Al-Li alloy profiles

Microstructure and mechanical properties of thixoforged complex box-type component of 2A12 aluminum alloy

Friction stir spot welding (FSSW) is a solid-state welding process, wherein the properties of a weld joint are influenced by the state of friction and localised thermodynamic conditions at the tool-workpiece interface. An issue well-known about FSSW joints is their lack of reliability since they abruptly delaminate at the weld-faying interface (WFI). This study explores the origins of the delamination of multiple lap welded aluminium alloy (AA 5754-H111) sheets joined by FSSW at different rotational speeds typically used in industry. Experimental techniques such as the small punch test (SPT), Vickers hardness test, Scanning Electron Microscopy (SEM), Scanning Acoustic Microscope (SAM), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and Frequency-Modulated Kelvin Probe Force Microscopy (FM-KPFM) were employed. The experimental results revealed that a complex interplay of stress-assisted metallurgical transformations at the intersection of WFI and the recrystallised stir zone (RSZ) can trigger dynamic precipitation leading to the formation of Al3Mg2 intermetallic phase, while metallic oxides and nanopits remain entrapped in the WFI. These metallurgical transformations surrounded by pits, precipitates and oxides induces process instability which in turn paves way for fast fracture to become responsible for delamination.

In-depth microscopic characterisation of the weld faying interface revealing stress-induced metallurgical transformations during friction stir spot welding

Refill friction stir spot welding (RFSSW) was applied to join the 2A12-T4 aluminum alloy successfully, and effects of the tool rotational speed on weld formation, microstructure evolution and mechanical properties of the RFSSW joint were investigated in detail. There existed macrostructure characteristics of bonding ligament and hook associated to the plasticized metal flow in the joint. The microstructure of the joint exhibited variations in the grain size, precipitates distribution and substructure in the width direction. A softened region existed in all the RFSSW joints and its formation could be attributed to the coarsening and dissolution of the S precipitates. Liquation cracks associated to the localized melting of S were observed in the stir zone of the joint produced at the highest rotational speed. The tensile-shear properties of the RFSSW joints were dependent on the hook geometry, distribution of the bonding ligament and hardness of the stir zone. With increasing the rotational speed from 900 to 1300 mm, the hook height increased, the bonding ligament at the weld periphery got more dispersed and the hardness of the stir zone decreased. The optimized RFSSW joint was obtained when the rotational speed was 1300 rpm, and the corresponding tensile-shear failure load was 10,030 N. Two different fracture modes, i.e. the shear fracture mode and shear-plug fracture mode, were identified in the tensile-shear tests.

Microstructural evolution and mechanical properties of refill friction stir spot welded alclad 2A12-T4 aluminum alloy

In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of al-clad 2A12-T4 aluminum alloy during refill friction stir spot welding. There are two material flow components, i.e., the inward- or outward-directed spiral flow on the horizontal plane and the upward- or downward-directed flow on the vertical plane. In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer. In the refill stage, this is process reversed. As such, there is no obvious vertical plasticized metal flow between adjacent layers. Welding leads to the coarsening of S (Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone. Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.

Xi-ming Wu

Papers

Microstructural evolution and mechanical properties of refill friction stir spot welded alclad 2A12-T4 aluminum alloy

Material flow behavior and microstructural evolution during refill friction stir spot welding of alclad 2A12-T4 aluminum alloy