Investigations on double-side friction stir welded aluminum alloy

Precipitation hardened high strength 7000 series aluminum alloys such as AA7075 are widely used in aerospace industry for structural applications and they are considered to be almost unweldable using conventional fusion welding processes. A solid state joining technique known as friction stir welding is found to be a suitable method to successfully join the plates of these high strength alloys, particularly AA7075. Nevertheless, the friction stir welding results in reduced weld properties and the reduction is more in case of thicker welds. Double-side friction stir welding is deemed to be one of the possible solutions to address the problem of weld property reductions. In this investigation, 10 mm thick AA7075-T651 plates were friction stir welded from both sides and the welds were evaluated for mechanical properties using tensile and impact tests. Weld microstructures and tensile fractures were also examined by optical and scanning electron microscopes. It was observed that double-side friction stir welding results in marginal improvement in strength values while percent elongation values do not show any improvement compared to that of single-side friction stir welds. The reasons for improvements in the weld properties are discussed, connecting mechanical behavior and weld microstructures.