Keyhole closure using friction spot welding in aluminum alloy 6061-T6

A new approach to refill keyholes using the friction spot welding (FSpW) technology was developed. Keyholes with a diameter of 7.5 mm in aluminum alloy 6061-T6 rolled sheets were filled with a cylindrical plug of the same material. Afterwards, the FSpW process joins the plug to the surrounding workpiece resulting in a sealed keyhole. Microstructural analysis and mechanical testing of keyhole closures have been performed. The mechanical properties have been determined in terms of microhardness, tensile strength, yield strength and elongation at fracture. Design of experiments and analysis of variance techniques were employed to evaluate the influence of the gas shielding, post-weld heat treatments and the plug itself on the properties of the welds. The experimental results demonstrate that the proposed method is suitable to refill keyholes in AA 6061-T6 and produce flawless joints with a superior surface appearance. The welds show high strength and hardness, especially when heat treatments are applied. The high strength of the welds were achieved at the expense of elongation at fracture, which is caused by a strengthened zone in the center of the welds. (C) 2016 Elsevier B.V. All rights reserved.