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.