FSW of AA2139-T8 Butt joints for aeronautical applications

The effect of process parameters on mechanical and microstructural properties of AA 2139 T8 joints produced by friction stir welding (FSW) was analysed by means of statistical tools. Three different parameters were taken into account: angular speed (ω), welding speed (va), and plunging depth (p); each of them was varied on three levels. Forces and temperatures achieved during the welding were monitored and analysed for all joints. An accurate microstructural analysis was performed: the occurrence of some remarkable defects, typical of FSW, such as tunnel or lack of penetration, was related to actual process parameters adopted.The extension of each FSW characteristic zone was measured and the main grain dimension within each of these zones was measured.The mechanical properties of the jointswere evaluatedbymeansofVickers microhardness measurements and tensile tests at room temperature. It was observed that the joint welded with lowest angular speed, highest welding speed, and greatest plunging depth attained the best performances. The statistical data treatment allowed providing a numerical model capable of predicting the mechanical performances of joints.