2.2. Welding Process

The welding process was performed on a milling machine (Metal Technics Polska s.c, Sokołów Podlaski, Poland) using a self-developed welding tool. Cylindrical threaded (Figure 1a) and tapered threaded (Figure 1b) shapes of the tool pins were used. The shapes are presented in Figure 1. In order to compare the effect of the shape of the welding tool used on the joint produced, five joints were made with each tool. To compare the welding parameters, nine more joints were made with the cylindrical threaded pin. A total of 19 butt joints were made in the flat welding position (PA). The tool plunge depth was 4.5 mm.

Sketch of tool pin shapes (dimensions in mm): (a) cylindrical threaded, (b) tapered threaded.

The parameters were selected on the basis of the high heat conductivity of the aluminium alloy plates [8,9] and high heat distribution obtained during FSW process [16]. Firstly, a rotational speed of 475 rpm was chosen as this was considered to be a low level that generated less heat [23]. The equal set of parameters were chosen to perform welding with different tool pin shapes. The same rotational speed (475 rpm) was maintained together with a variety of welding speeds ranging from 150 to 475 mm/min. On the basis of primary visual tests of the specimens made at 475 rpm, a welding speed of 300 mm/min was chosen for further parameter examinations. Seven joints were made using a cylindrical threaded pin at the above-mentioned welding speed as well as a variety of rotational speeds ranging from 115 to 925 rpm. Two additional joints were made at the same rotational speed (475 rpm) and welding speeds of 95 and 600 mm/min for more accurate results. The parameters used are presented in Table 2.

Welding parameters.