Friction stir welds made out of precipitation hardenable aluminum alloys–experimental investigations of formability potential

Abstract

The industrial application of aluminum alloys in lightweight constructions is basically connected to two fundamental manufacturing requirements. First, the formability of aluminum blanks must be adequate in order to shape the required geometries. This requirement can be fulfilled by using precipitation hardenable aluminum alloys which can be formed well in natural aged condition. In common, these alloys are artificially aged afterwards for getting a higher strength. Second, suitable joining technologies must be available for connecting the formed elements to a complex lightweight construction. One such joining technology could be friction stir welding (FSW), because of better mechanical properties due to lower heat input compared to other joining technologies, for example laser welding. Thereby also Tailored Welded Blanks (TWB), which are used for reducing the number of parts or for locally reinforcing structures, can be used for aluminum lightweight constructions. Beside these attributes dominated by production technology weld seams must also fulfill utilization based requirements. One such criterion is that a misapplication of aluminum lightweight constructions, which are commonly used in transportation systems, is not leading to a complete failure. Therefore aluminum joints, which are connecting the formed parts, should have certain formability to balance a local overstraining. For the implementation of this consideration the formability of FSW joints made out of AA6016 aluminum is investigated in this paper. Therefore local martens hardness distribution of unformed, formed and artificially aged welds are conducted and the results are compared to each other.