Friction Stir Welding of advanced aluminium alloys for new aircraft generation

To achieve the objective of aircraft weight reduction, in collaboration with Sonaca aerospace company, the aim of this master thesis is to perform the friction stir welding (FSW) of the advanced aluminium alloy 5028. AA5028 alloy is a 5xxx series aluminium alloy containing a small amount of Sc and Zr that presents a low density, a good resistance to corrosion and a high-strength due to an un-recrystallised microstructure after hot and cold rolling processes. By means of mechanical tests and analyses of the grain sizes, the effect of the FSW parameters on this alloy was studied to avoid a significant loss of strength in the weld. For the best welding conditions, a FSW joint efficiency of more than 91% was obtained. The impact of a thermal treatment corresponding to the one of the creep forming is investigated as this forming process provides elaborate curvature panels with a good surface finish. The influence of this thermal treatment on the microstructure and on the mechanical performances of the weld was investigated. As this treatment only slightly influenced the mechanical properties, it demonstrates that the FSW of AA5028 followed by creep forming opens the door to the design of integral structures for aircraft weight reduction.