Abstract
The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 aluminium alloy sheet blanks was studied by performing experiments with constant values of the rotational speed, varying between 1200 and 2500 rpm, and welding speed, ranging between 30 and 100 mm/min. The effect of the tool dwelling was also analysed. The force vs. processing time curve has shown a very complex behaviour during the lowering motion of the pin tool related to the occurrence of both primary and secondary plunging. The tool dwelling produces a quick decrease in the vertical force with growing processing time until reaching a constant value. It was also seen that the tool dwelling does not influence the vertical force in the subsequent stage. As the tool began its welding motion, the vertical force immediately gets to a constant value until tool pulling out takes place. Furthermore, it was shown that the growth in the welding speed and the decrease in the rotational speed lead to an increase in the vertical force. The mechanical properties of the joints were evaluated versus the process parameters and the relationships among the ultimate tensile strength and ultimate elongation and the vertical force were defined. Finally, the microstructure developed during the friction stir welding was investigated and related to the mechanical properties of the joints.
Highlights
In friction stir welding (FSW), the shoulder of a non-consumable rotating tool rubs onto the surface of the sheets to be welded and produces heat; at the same time, the pin of the tool exerts a stirring action into the sheet edges
It was shown that the vertical force vs. time curve, as well as the workpiece temperature, strongly depend on the rotational and welding speeds, according to the results shown by other authors in [20,21,22]
The influence of the process parameters on the vertical force generated during friction stir welding of AA6082-T6 sheet blanks was studied
Summary
In friction stir welding (FSW), the shoulder of a non-consumable rotating tool rubs onto the surface of the sheets to be welded and produces heat; at the same time, the pin of the tool exerts a stirring action into the sheet edges. Under suitable process conditions, FSW can allow the obtaining of a microstructure able to provide mechanical properties much higher than those of most fusion welding processes and formability levels so high that post-welding forming processes of welded blanks can be performed Because of these advantages, FSW can be very useful both in joining materials with poor weldability or that are un-weldable, such as aluminium and magnesium alloys, and in the obtaining of joints characterised by high efficiency [1,2,3,4,5,6,7,8,9,10,11]. The highest values of the ultimate tensile strength and ultimate elongation were obtained under rotational and welding speeds characterized by the lowest vertical force and highest temperature. The microstructure derived from the FSW experiments was studied and related to the mechanical properties of the joints
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