Friction stir blind riveting is a new joining process for one-sided joining (compared with the two-sided access required for, for example, self-piercing riveting) of aluminum alloys, which eliminates the need to predrill a hole for rivet insertion. A blind rivet rotating at high speed is brought into contact with the workpieces, thereby generating frictional heat between the rivet and the workpiece, which softens the workpiece material and enables the rivet to be driven into the workpieces under reduced force. Once fully inserted, the blind rivet is upset using the internal mandrel (as in a conventional blind riveting process) to fasten the workpieces together. Our study showed that friction stir blind riveting process can be carried out over a wide range of operating parameters. The resulting joints show consistent strength under tensile load with minimal influence of changes in operating parameters. The robustness of the process against variations in operating conditions shows that the process can be carried out without high-end equipment and without requiring precise initial setup. It also suggests that the process is feasible for rapid joint fabrication in volume production. Further study revealed superior static and fatigue strength from the friction stir blind riveting process, when compared with conventional spot welding, which suggests potential for reduction in the number of joints required in a structure.

The high strength-to-weight ratio of magnesium alloys makes them attractive for automotive applications. These materials have been used for the engine cradle, seat frame, and shock tower applications to reduce vehicle weight. Despite these advantages, there are limiting factors to the application of magnesium alloys. One of these factors is the joining of magnesium alloys. Although there are various joining processes available, self-piercing riveting (SPR) is particularly promising. It provides not only the speed but also the necessary structural strength. However, because of the large amount of deformation associated with the process and the limited formability of magnesium at room temperature, SPR often results in part cracking of the riveted magnesium alloys, which reduces the part quality. In this study, a method of preheating the magnesium alloy before riveting was adopted to improve the joint quality. The fabrication of the desired SPR joints was investigated as a function of the preheat temperature and strain rate. To determine the optimum preheat temperature, Zener–Hollomon parameter was employed. Experiments were conducted to validate the proposed preheat temperature. Magnesium alloy AZ31 with a thickness of 2 mm was preheated with various temperatures prior to self-piercing riveting. The appearances, cross-sections, and mechanical tests of the SPR magnesium AZ31 joints were investigated. It was found that a preheat temperature of 180–200°C largely eliminated the discrepancies in SPR 2 mm thick magnesium AZ31 joints. The joint strength increases with increasing preheat temperature from ambient to 200°C. The strength increase is attributed to the reduction in joint discrepancies and an increase in mechanical interlock between the rivet and work pieces. The current findings on the development of a method can be used to determine the preheat temperature for self-piercing riveting of magnesium castings.

In this study, weldability of ultrasonic welding of 4-mm-thick fiber carbon/nylon 66 composite in lap configuration was investigated. Ultrasonic welding tests were performed, and the weld appearance, microstructure, and fractography of the welded joints were examined using optical and scanning electron microscope. The transient temperatures near the faying surfaces and horn-workpiece interfaces were recorded to understand the weld growth mechanism. It was found that it is feasible to join 4-mm-thick lapped carbon fiber reinforced nylon 66 composite with ultrasonic welding. Under the ultrasonic vibration, the weld initiated and grew at the faying surfaces, while the weld indentation developed at the horn-workpiece interface. The pores observed in the regions between the heat-affected-zone (HAZ) and the fusion zone (FZ), and the severe weld indentation on the surface of upper workpieces decreased the loading capacity of the ultrasonic welded (UW) joints and caused the welded carbon/nylon 66 composite fractured prematurely. The strengths of the ultrasonic welds were determined by the balance of positive effect of the weld area and negative effects of the weld indentation and porosity near the FZ. To ensure the joint strength, it is necessary to apply the proper weld schedules (i.e., welding time and horn pressure) in ultrasonic welding of 4-mm-thick carbon fiber reinforced nylon 66 composite, which were developed based on the joint strength criterion.

Mechanical clinching method has been shown to be a feasible alternative to self piercing riveting (SPR) for joining dissimilar materials, particularly for vehicle assemblies made in aluminum-to-steel. While a great deal of effort has been focused on studying the process development, there is an urgent need to understand the effects of aged aluminum on the strengths of the clinching steel-aluminum joints. To evaluate exactly the influence of mechanical properties of aged aluminum alloy on the strength of the clinching joint, 1.0 mm thick AA6111-T4 aluminum was firstly solution heat-treated at 550 °C for 30 min followed by nature ageing treatment for various times and then clinching to 0.7 mm thick galvanized SAE1004 steel with SKB die. The section parameters and strength of the clinching joints were measured. The effect of mechanical properties of aged AA6111-T4 aluminum was analyzed using an analytical model. The results showed that aged aluminum affected little the clinchability but influenced the section parameters and strength of the clinching workpieces. The strength of the clinching SAE1004-to-AA6111-T4 joints increased with increasing the strength of AA6111-T4 aluminum. This can be primarily attributed to the fact that the strengthening AA6111-T4 aluminum resulted in larger residual press stress developed during the clinching.

In this study, cold metal transfer (CMT) plug welding of 1 mm thick Mg AZ31 to 1 mm thick hot-dipped galvanized mild steel (i.e., Q235) was studied. Welding tests were performed and the process variables optimized with Mg AZ61 wire and 100% argon shielding gas for a plug weld located in the center of the 25 mm overlap region. It was found that it is feasible to join 1 mm thick Mg AZ31 workpiece to 1 mm thick galvanized mild steel using CMT plug welding. The optimized process variables for CMT plug welding Mg AZ31-to-galvanized mild steel were a wire feed speed of 10.5 m/min, a predrilled hole with a diameter of 8 mm in Mg AZ31 workpiece and a welding time of 0.8 s. CMT plug welded Mg AZ31-to-galvanized mild steel joints were composed of the fusion zone between Mg AZ31 base metal and Mg weld metal, Mg weld metal (i.e., combined base metal, filler wire and Zn coating), and the brazing interface between magnesium weld metal and galvanized mild steel. The brazing interface mainly consisted of Al, Zn, Mg, Si intermetallic compounds and oxides (i.e., Fe₃Al, Mg₂Si, MgZn, and MgZn₂), and magnesium solid solution. The static strength of CMT welded-brazed Mg AZ31-galvanized steel was determined primarily by the strength and area of the brazed interface and thickness of the intermetallic reaction layer.