Performance of Friction Stir Welded Tailor Welded Blanks in AA5059 and AA6082 Alloys for Marine Applications

Abstract

Tailor welded blank (TWB) concepts in aluminum alloys, welded by friction stir welding (FSW), are an attractive solution to reduce structural weight of structures applied on the transportation sector. In the present work the mechanical performance and microstructural features of dissimilar friction stir welded TWBs were assessed. Welds were produced with alloys of particular interest to the shipbuilding sector (AA6082 and AA5083, with a thickness combination of 6 and 8 mm respectively) and the effect of rotational speed on the weld properties was investigated. A digital image correlation system (DIC) was used to characterize the local strain fields during the quasi-static tensile tests. Microstructure analysis revealed the presence of a remnant oxide line (ROL) at the stir zone. Moreover, the rotational speed directly affected the ROL distribution and consequently the mechanical properties of the welds. The TWB produced with low rotation speed and high force (600 rpm and 20kN) has shown the highest mechanical performance and failed at the thermo-mechanical affected zone of the AA6082 plate. The micromechanisms of fracture were assessed by SEM and revealed a ductile fracture with large amounts of dimples spread out on the fracture surface.