In friction stir welding of heat treatable aluminum alloys, the thermal cycles developed during the joining process result in softening of the joints which adversely affect their mechanical properties. Underwater friction stir welding can be a process of choice to overcome this problem due to low peak temperature and short dwell time involved during the process. Consequently, this article presents a study pertaining to the underwater friction stir welding of aluminum alloy 6082-T6 with an aim to develop a mathematical model to optimize the underwater friction stir welding process parameters for obtaining maximum tensile strength. The results of the study reveal that the tool shoulder diameter (d), tool rotational speed (ω), welding speed (v), and second-order term of rotational speed, that is, ω2, significantly affect the tensile strength of the joint. The maximum tensile strength of 241 MPa which is indeed 79% of the base metal strength and 10.7% higher than that of conventional (air) friction stir welding joint was achieved at an optimal setting of the underwater friction stir welding parameters, that is, tool rotational speed of 900 r/min, the welding speed of 80 mm/min, and a tool shoulder of 17 mm. The article also presents the results of temperature variation, the macrostructural and microstructural investigations, microhardness, and fractography of the joint obtained at the optimal setting for underwater friction stir welded (UFSWed) joint.

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In the recent years, metal foams have become promising candidate materials in the engineering sector owing to their light weight and excellent energy absorption properties. Friction stir processing (FSP) has emerged as a cost-effective route to fabricate metal foam precursors from bulk substrates. Although the short processing time in FSP is able to provide high productivity, the cost of the foaming agent, TiH 2 in the case of aluminum foams is still high. This paper introduces flame heating to achieve localized foaming of aluminum alloy AA5754 to explore the possibility of using magnesium carbonate as a foaming agent stirred using multi-pass FSP. A specially designed slot based strategy using two plates arranged in lap configuration is devised to stir the foaming agent and understand the material movement after each subsequent pass. Microscopy techniques were carried out to evaluate the distribution of the foaming agent after each pass and the resulting microstructure of the processed plates as well as the morphology of the foamed sample. EDX results showed higher Mg and O content around the pore walls.

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