Friction Stir Welding (FSW) is one of the excellent metals joining processes in terms of joint strength efficiency, quality of the weld and eco-friendliness. The strength of the joint and quality of the weld depend upon the FSW processing parameters. This paper aims to provide overview of the FSW process by considering the effect of alloying elements and its precipitates on mechanical properties of aluminium and its alloys. The importance of grain growth and its effect on mechanical properties after welding is also analysed and discussed in detail. The interesting observation is that the precipitates and its size, residual stress play an important role in changing the hardness, tensile strength and fatigue strength across the weld zones. In general, the hardness of the stir zone is lesser when compared to base metal and this is noticed for all series of aluminium and its alloys, irrespective of the precipitates and its structure. Grain size and its morphology also have significant role in affecting the mechanical properties of the welded joint and it is found that post welding process has noticeable effect on the mechanical properties closer to base aluminium and its alloys.

Aerospace alloys with reduced wall thickness but possessing higher hardness, good tensile strength and reasonable corrosion resistance are essential in manufacturing of structures such as fuselage. In this work, friction stir welding has been carried out on such an aerospace aluminum alloy AA8090 T87 which contains 2.3% lithium. Tool rotational speed of 900 rpm and traverse speeds of 90 mm/min., 110 mm/min. are the welding parameters. Hardness analysis, surface roughness analysis and corrosion analysis are conducted to analyze the suitability of the joint for the intended application. The samples were corrosion tested in acid alkali solution and they resulted in the formation of pits of varying levels which indicate the extent of surface degradation. Hardness of the samples was measured after corrosion analysis to observe the changes. The analysis suggests that the change in tool traverse speed transformed the corrosion behavior of the joint and affected both the hardness and surface roughness which mitigated the quality of the joint.

The aerospace industries are focused on lightweighting with alloys having good tensile strength, fracture toughness, fatigue resistance, and corrosion resistance. The friction stir welding technology is one of the productive techniques in the aerospace industry to join such alloys with little ease. This paper deals with the composition of alloying elements that makes the structure lightweight and the impact of the precipitates evolved out of the selected alloying elements on the mechanical properties such as tensile strength and hardness of the joint in the aerospace alloys such as AA2xxx conventional aluminium alloys, AA2xxx lithium-based aluminium alloys, and AA7xxx aluminium alloys.

The aerospace alloy AA8090 T87 was friction stir welded with varying traverse speeds of 30 and 70 mm/min at rotation speeds of 900 and 1100 r/min to realize the effect of traverse speed and rotation speed on the joint strength. This variation in the rotation and traverse speeds produced variation in the thermal cycle in the weld joint that altered the microstructure of the stir zone and morphology of the grains. The increase in the rotational speed from 900 to 1100 r/min at 30 mm/min increased the grain size from 4.1 µm to 7.8 µm in the stir zone which was evident from the microscopy images and Schmid factor maps and contributed to the mechanical property changes. The increase in traverse speed from 30 to 70 mm/min has led to the hardness improvement and reduction in grain size in the stir zone. The nature of the fracture observed in the stir zone is ductile fracture having more dimples. An effective joint was produced at 900 r/min rotational speed and 30 mm/min traverse speed.

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