This review sheds novel insights on the residual oxide behaviour of solid-state weld joints of aluminium alloys. Understanding the influence of oxides on the aluminium surface before and during ...welding, its impact on the weld structure and possible solutions for reducing its impact were addressed. The solid-state techniques most relevant to the transportation sector namely, diffusion bonding, friction stir spot welding and ultrasonic welding were surveyed, analysed and reviewed. During this analysis, the implication of the presence of oxides on aluminium substrate affecting the metallurgical characteristics of the weld joints was reviewed. Visible defects such as voids, delamination, kissing bond and hook defects, and problems associated with these defects were analysed and few suggestions are made to partially overcome these issues.
Abbreviations: AS, Advancing side; CDRX, Continuous dynamic recrystallisation; CFSSW, Conventional friction stir spot welding; DB, Diffusion bonding; EDS, Energy-dispersive spectroscopy; e-TEM, Environmental transmission electron microscopy; FSW, Friction stir welding; FFSSW, Flat friction stir spot welding; FSSW, Friction stir spot welding; IPDB, Impulse pressuring diffusion bonding; IPADB, Impulse pressure-assisted diffusion bonding; PLT-FSSW, Pinless tool friction stir spot welding; PFSSW, Protrusion friction stir spot welding; RFSSW, Refill friction stir spot welding; RS, Retreating side; RZ, Recrystallised zone; SEM, Scanning electron microscopy; TEM, Transmission electron microscopy; TWI, The Welding Institute; USW, Ultrasonic welding; WFI, Weld faying interface; WFSSW, Walking friction stir spot welding; XPS, X-Ray Photoelectron Spectroscopy
Ultrasonic welding (USW) of Titanium (Ti) sheets presents several challenges, notably crack formation due to sliding friction. To overcome this problem, the present study applied USW to pure α-Ti ...sheets both with and without different interlayer metals (Al, Ni, and Fe). Al interlayer improved the strength at room temperature significantly to cause base metal fracture (1700 N) by inducing concentrated plastic deformation, facilitating bonding with Ti while minimizing damage. However, its strength decreased significantly at 150–300 °C, suggesting the limitation of using Al interlayer at elevated temperatures. Conversely, the Ni and Fe interlayers led to a two-phase strength development. This enhancement was due to β-phase transformation, which reduces the interfacial defects and generates a more pronounced β-stabilization effect. The Ni interlayer, which has a higher β-transus point (765 °C) and lower molybdenum equivalency, required a higher welding energy (1800 J) and longer diffusion time into Ti, resulting in a gradual increase in strength due to a slower β-Ti transformation. On the other hand, the Fe interlayer with a lower β-transus point relative to Ti (595 °C) achieved peak strength at a lower welding energy of 1200 J. Both Fe and Ni interlayers displayed only a slight decrease in strength (1500–1600 N) at 300 °C with base metal fracture, revealing better joint performance at higher temperatures. These insights suggest a strategical interlayer selection based on the operation temperature, where Al interlayers were advantageous for low-energy welding at room temperature application, Fe and Ni interlayers offer sufficient strength at elevated temperatures by facilitating the β-Ti formation.
Nonwovens have wide application areas due to their advantageous properties like low cost, high production efficiency, and tuneable properties. They are mostly used for disposable products. Combining ...bicomponent fiber spinning with hydroentanglement method is one of the innovative methods to obtain nonwovens for durable applications. On the other hand, ultrasonic welding is an alternative assembling method for disposable products made of low weight nonwovens. In this study, the ultrasonic weldability of relatively heavier weight and thicker nonwoven fabrics made of polyester: polyamide bicomponent microfilaments were examined in order to combine the advantages of nonwovens and ultrasonic welding. Relatively higher thickness and weight, and also fiber composition of the nonwoven fabrics were compelling effects of the study that drove the motivation. Overall 60 samples were produced using five nonwoven fabrics with varying unit masses and 12 selected ultrasonic welding types. Seam strength and strain assessments were supported with stereomicroscope and visual inspections in evaluating the welds. Results showed that despite having thick seam lines up to 1.6 mm, successful welded seams could be obtained. Depending on the welding parameters, seam lines of some samples exhibited waviness, color changes, and deformations but these situations did not drastically affect the seam strength of samples.
Ultrasonic welding conditions and test results.
•A multiphysical model of the ultrasonic welding process was developed.•Dry friction at the interface and bulk viscoelastic heating were taken into account.•Extensive material characterization was ...performed for thermoplastic PEI to input in the model.•The predicted dissipated power compares well with experimental measurements.•The model provides a realistic prediction of the temperatures in the welding area, which is difficult to measure accurately.
A model for the mechanics (oscillating deformation), heat transfer including viscoelastic heat generation and friction dissipation, and degree of adhesion (intimate contact and healing) is proposed for the initial transient heating phase.
Numerical resolution was performed using a multi-physical finite element code. The predicted dissipated power evolution exhibits a good correlation with previous experimental measurement of delivered power, and shows that the apparatus has a global efficiency of 13%. The predicted degree of adhesion also confirms the experimental observation that adhesion starts at the edge of the contact area, and progressively extends to the whole contact area.
The numerical model was further used to investigate the physical mechanisms occurring during the welding process. As suggested in the literature, the first heating mechanism is confirmed to be due to interfacial friction. Bulk viscoelastic dissipation becomes predominant when the interface reaches higher temperatures. The dissipated power is suddenly increased when the whole interface reaches the glass transition temperature.
Changes in bonding strength and interfacial formation during the ultrasonic welding (USW) of steel and Ti were investigated. It was found that when the temperature of the joint was increased above ...600 °C during USW, the bonding strength increased drastically and resulted in base-metal fracture. Interfacial, fracture, compositional, and crystallographical analyses revealed that phase transformation in Ti from α (hexagonal close-packed: HCP) to β (body-centered cubic: BCC) led to improved deformability at elevated temperatures, which promotes extensive bonding formation through the elimination of gaps near the bonding interface. Through this process, joints with good bonding and strength can be obtained.
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