Friction stir processing (FSP) stands as an effective approach designed for grain refinement and site-specific microstructural modification. The evolving microstructure during FSP is determined by various variables out of which rate of sample cooling is the key parameter. More often, FSP is conducted in naturally flowing air; however, a large number of studies are conducted by researchers across the world; stressing the importance of additional sample cooling strategy for tailoring the material microstructure. Such strategies vary not only in terms of the cooling medium used but also with regard to various other compliant conditions that must be fulfilled for the cooling process to make them successful and economically viable. This work critically reviews the most prevalent methods practiced by various researchers and industries for controlled sample cooling during and after FSP. The underlying mechanisms; advantages; disadvantages; and limitations of each procedure along with the resulting microstructure and material performances are discussed and recommendations are provided

Magnesium (Mg) alloys, owing to their lightweight, have gained substantial attention in industries such as aviation and automotive. Researchers are continuously working on different strategies to improve the performance of Mg alloys, among which alloying is of prime importance. However, care has to be taken so as to avoid over alloying of Mg as that would degrade the lightweight advantage of Mg. Addition of gadolinium (Gd) and yttrium (Y) to magnesium holds promise for improving mechanical performance, but a detailed comprehension of their synergetic effect on alloy’s microstructure and deformation behaviour is crucial, which forms the basis of this study. Mg alloys with varying percentage of Gd and Y are developed in this study using gravity casting method. Microstructural assessment revealed a complex interplay of phases, including the presence of eutectic structures among other strengthening precipitates. Distribution and morphology of these microconstituents are studied in detail through electron microscopic techniques. Mechanical performance of the materials is assessed through tensile testing. Results indicated that the incorporation of Gd and Y influenced critical resolved shear stress (CRSS) values, affecting the activation of specific slip systems and twin systems. Post-deformation analysis preformed through fractography provided valuable information on the fracture modes and failure mechanisms, contributing to a comprehensive understanding of the alloy’s reliability. Mechanisms leading to a typical microstructure and a resultant mechanical performance for Mg-Gd-Y alloy is discussed in detail.