Friction stir processing (FSP) is an important microstructural alteration process used recently in the engineering field. Grains alteration and hence the mechanical properties of the possessed zone are controlled by the temperature, heating and cooling rate. In this work, AZ31B magnesium samples were friction stir processed in three different cooling conditions like air, water and cryogenic (liquid nitrogen) cooling. 1000 rpm and 60 mm/min were kept constant as tool rotation speed and traverse speed respectively in all the three mediums. The consequence of these conditions on thermal fields, axial force, resulting grain structure and mechanical properties was studied. It is found that the cryogenic treated friction stir processed samples exhibit fine grain structures and hence offer better mechanical properties than the air and water cooled processed samples.

In this study, an effort has been made to choose an appropriate tool pin profile and rotational speed for a tool using a submerged friction stir processed hot rolled AZ31B magnesium alloy. A defect free process region was obtained using a novel tool shoulder, which consisted of a scroll. Three tool pin profiles, namely, simple cylindrical, stepped cylindrical and stepped square pin have been used. Tensile properties and fracture behavior revealed defect free friction stir processed specimens. The microstructural studies reveal the possibility of producing a defect free processed region using the stepped square pin tool geometry. The presence of fine recrystallized grains (1.99 µm) and the absence of defects in the processed region lead to higher hardness and superior tensile properties.

Friction Stir Welding (FSW) is currently used in many aircraft and aerospace sheet metal structures involving lap joints and there has been growing interest in recent years in utilizing this process for joining aluminum alloys. In this paper, Friction Stir Lap Welding (FSLW) of the 6061-T6 aluminum alloy was carried out to obtain the optimum welding condition for maximum shear strength where the rotational speed, axial load, and welding speed were taken as process parameters. An L-9 orthogonal array, a Taguchi Method with consideration of three levels and three factors was designed and executed for conducting trials. Analysis of variance (ANOVA) and Signal to Noise (S/N) ratio were employed to investigate the influence of different welding parameters on the shear strength and obtain the optimum parameters. The Fisher-Test was also implemented to find the design parameter which had the most important effect on the characteristic of quality. The results indicated that the tool rotational speed had the maximum percentage contribution (51%) on the response (shear strength) followed by the welding speed (38%) and the axial load (8%) while the percentage of error was 3%. However, to confirm the main effects for the means and S/N ratios of the experiment, theoretical shear strength values were computed to predict the tensile strength. The maximum shear strength of 60 MPa was achieved and the effectiveness of the method was confirmed. The optimum parameter combinations that provided higher shear strength were: rotational speed of 1200 rpm, welding speed of 45 mm/min and the axial load of 11.5 kN.

Friction stir welding (FSW) invented by TWI is a solid-state joining process, which is used to weld high-strength aluminum alloys and other metallic alloys which are non weldable by conventional fusion welding process. In this work, AA6063-O alloy of 150 mm in length, 75 mm in width and 6mm thickness is taken and friction stir welded in submerged condition in order to improve the joint properties. The chosen process parameters are tool pin profiles (cylindrical, threaded and tapered), rotational speed and welding speed. The process parameters are optimized with multi response characteristics including hardness and average grain size at the nugget zone. The traditional Taguchi approach is insufficient to solve a multi response optimization problem. Therefore, Grey Relational Analysis (GRA) is used in this current work. The optimal result indicates that the multi response characteristics of the AA6063-O during the submerged friction stir welding process can be enhanced through Grey Relational Analysis. In order to investigate the significance of process parameters, Analysis of Variance (ANOVA) is carried out. The mechanical properties and microstructure variation of both the normal FSW and submerged FSW joints are compared.

In this research, friction stir processing of AZ31B magnesium alloy of 6 mm thickness was done in submerged conditions. The process parameters, i.e. tool pin profile (simple cylindrical, stepped cylindrical, stepped square), rotational speed ranging from 800 to 1200 rpm and traverse speed ranging from 0.5 to 1.5 mm/sec were optimized using the multi response optimization technique. The experiment was conducted with L27 orthogonal arrays. The Immersion test and hardness have been considered as output response. From the view of an application, it would be more significant to optimize the Immersion Corrosion rate and Hardness of Submerged Friction Stir Processed AZ31B alloy. Thus, this study aims at optimizing the process parameters, including various tool pin profiles, feed rates and rotational speeds with corrosion rate and micro hardness using TOPSIS. Using analysis of variance (ANOVA), the most significant parameter effect of the submerged friction stir processing was determined.