Abstract
Refill friction stir spot welding (RFSSW) is an innovative solid-state welding technology for aluminum structures. The presented study aimed to evaluate the mechanical properties of refill spot welds and their failure mechanisms with the use of industrial test standards. The mechanical properties of refill spot welds were compared with those of rivet joints with comparable joint sizes. Static load tests indicated that RFSSW coupons demonstrate higher ultimate shear strengths but slightly lower ultimate tension strengths than those of rivet coupons. Fatigue test results indicated that both RFSSW coupons and rivet coupons demonstrate comparable performances during low-load-level fatigue lap shear tests but RFSSW coupons outperform rivet coupons during high-load-level fatigue lap shear tests. The failure mechanisms of refill spot welds were characterized in terms of external loading, parent metal properties, and weld properties. Refill spot weld failures included parent metal tensile failures, nugget pullouts, and interfacial failures. A refill spot weld may demonstrate one or a combination of these mechanical failures. Although the mechanical tests of refill spot welds demonstrated promising results with predictable failure mechanisms, the metallurgical evolution involved in RFSSW remains a subject to study.
Highlights
The use of aluminum alloys is steadily increasing as they are light in weight, environmentally friendly, and easy to recycle
The workpieces used in this study are high-strength aerospace aluminum alloys workpieces
Industrial standards that are typically used for testing rivet joints were implemented in this study to evaluate the mechanical properties of refill spot welds
Summary
The use of aluminum alloys is steadily increasing as they are light in weight, environmentally friendly, and easy to recycle. They are widely used in aircraft structures, automotive applications, and various consumer products. Conventional joining methods, such as riveting, fusion welding, and resistance spot welding, can establish sound welds or joints of aluminum alloys with satisfactory mechanical properties [1,2]. The aerospace industry uses riveting as a standard fastening method as it meets the baseline requirements and has well-established standards and specifications. Producing good aluminum joints using innovative welding techniques remains a challenge
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