Effect of tool pin profile on the tensile characteristics of friction stir welded joints of AA8011

Introduction. Aluminum alloys are in abundant demand of shipbuilding and aircraft industries. This study emphasizes on the effects of two different tool pin profiles on the tensile characteristics of welded joints made of AA8011 aluminum alloy welded joints. The joining technique used is friction stir welding (FSW) due to its unique characteristics such as very low heat affected zone when joining in a solid state. The microstructure and mechanical properties of the welded joint are influenced by the geometry of the tool and such parameters as rotational speed and traverse speed of the tool. The methods of investigation. The experiments on FSW were performed on universal milling machine with taper cylindrical and cylindrical threaded tool pin profiles using the three different combination of tool rotational and traverse speed (a) 320 rpm, 45 mm/min; b) 400 rpm, 50 mm/min; c) 575 rpm, 60 mm/min.). To analyze the joint characteristics, tensile tests were conducted and ultimate tensile strength as well as joint efficiency was calculated for individual joint. Results and Discussion. Based on the revised results, it is evident that higher RPM values have a positive impact on joint efficiency and tensile strength for both the taper cylindrical pin profile and the threaded cylindrical pin profile. The findings show that the joint efficiency and tensile strength are consistently higher for the threaded cylindrical pin profile compared to the taper cylindrical pin profile, regardless of the RPM and feed rate. From the results, it was found that joint efficiency and tensile strength is maximum at higher RPM irrespective of the tool pin profile i.e. 73.6 % and 123 MPa for taper cylindrical pin profile and 85 % and 142 MPa for threaded cylindrical pin profile at 575 rpm, 60 mm/min. These are the highest in comparison to 72.5 % and 119 MPa at 320 rpm, 45 mm/min and 70.1 % and 115 MPa at 400 rpm, 50 mm/min for taper pin profile tool and 82.6 % and 138 MPa at 320 rpm, 45 mm/min and 77.8 % and 130 MPa at 400 rpm, 50 mm/min for threaded cylindrical pin profile. Overall, the study demonstrates that joints obtained using the threaded cylindrical pin profile demonstrate higher joint efficiency and tensile strength than those prepared using the taper cylindrical pin profile. The highest joint efficiency and tensile strength of 84.5 % and 142 MPa, respectively, were achieved using the threaded cylindrical pin profile at 575 rpm and 60 mm/min.