The influence of process parameters and tool geometry on mechanical properties of friction stir welded aluminum lap joints

The results of an experimental investigation on the lap joining of AA6022-T4 aluminum alloy blanks by FSW are reported in the present paper; in particular, the joints strength was investigated. The experimental campaign was performed on sheets having a thickness of 1.2 mm, lap joined by means of a CNC machine tool. Several tests were carried out by varying process parameters (namely feed rate and rotational speed), joints configuration and tool geometry (two different tools were adopted for this purpose). The first tool was a very simple device with a flat shoulder and a cylindrical pin. The second one was a more complex tool, with a flat shoulder and a threaded probe. During these tests welding forces were also measured. A universal testing machine was employed to evaluate the strength of the friction stir welded joints as a function of the different process conditions. Interesting results in terms of tensile strength of the joints were obtained using both the simple and the threaded tools. In particular it was found that the use of threaded pin tools and the correct choice of the relative sheet positioning may lead to the improvement of the mechanical properties of the obtained joints. Moreover, the use of the threaded tool showed a certain reduction in welding forces, with respect to the simple tool.