Effect of rotational speed on joint integrity of friction stir lap welded aluminium

Friction stir welding is a newly developed solid state welding process, which was developed by The Welding Institute in the year 1991. The development of FSW has allowed the process to be used in different applications for different industries, which include aerospace and automobile industry. Due to the increase in the demand of high strength and low weight components in different manufacturing applications, there is a need for using pure aluminium and its alloys in lap configuration. Research studies are required to characterize and obtain optimum process parameters, which can be used to produce good quality lap welds. This paper reports lap welded 1050 Aluminium Alloy using friction stir welding process and established the effect of rotational speed on the joint integrity of the welds. The welds were produced by varying the rotational speed in the range of 1200 and 2000 rpm, and maintaining the traverse speed constant at 150 mm/min. The welds were characterized through microstructural evaluation, microhardness profiling and tensile testing in order to determine the joint integrity of the welds. The results from the macrograph of the welded joints, show a basin shaped nugget resulting from the stirring of the tool during the welding process. Fine and equiaxed grains characterized the microstructure in the stirred zone, which was a result of a dynamic recrystallization. The tensile test data revealed that as the tool rotational speed was increased, the fracture strength also increases, the highest value of the fracture strength was 195 N/mm and was found on the welds produced at 2000 rpm. High Vickers microhardness values were measured at the nugget zone with the highest value found to be 31.88 HV. It was revealed that the welds produced at the rotational speed of 2000 rpm exhibited the optimum welding parameters to join 1050 Aluminium Alloy.