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The demand for tailored properties of the materials and lightweight characteristic accelerates the development of metal matrix composites (MMCs). The conventional methods of MMCs development require several post-processing techniques like a microstructural modification or grain refinement, to fulfil the desired requirement of specific applications. In this regard, friction stir processing (FSP) can be proved as an alternative, not only for microstructural modification but also utilized for the development of surface composites. This solid-state approach is an environment-friendly process. It also refines the grain structure of the alloys and composites, which in turn, enhances the mechanical properties such as tensile strength, hardness and fatigue strength. The present work aims to focus on the state of the art research in the field of friction stir processing and to highlight its key points and merits over traditional methods. The present work also emphasizes the developments in friction stir processing, especially on aluminium and magnesium-based alloys and composite and futuristic approaches adopted in various industrial application. • The present work focusses on friction stir processing and highlights the key points and merits of FSP. • It also emphasis the developments in FSP work especially on aluminium and magnesium alloys and composite. • The effect of process parameters related to heat generation, material flow and tool pin profile is explored. • Microstructural, mechanical characterization, and grain refinement are some keen point of the present work. [ABSTRACT FROM AUTHOR]

This study focused on the development of an AZ31B/Si 3 N 4 /Eggshell surface composite via solid-state multi-pass friction stir processing. The study aimed to characterize the developed surface composite based on its structural, microstructural, mechanical, and tribological performance at one, two and three successive tool-passes. The structural and compound analysis was conducted using an XRD pattern. Microstructural characterization and grain refinement studies were conducted using FESEM images and EBSD analysis. Furthermore, the mechanical properties were investigated through tensile tests equipped with digital image correlation (DIC) images and fractography analysis via FESEM images. In addition, tribological characteristics, such as COF, friction forces, and volumetric wear losses, were examined using a universal tribometer, and the 3D profile of the wear track was analyzed through surface profilometry. The results revealed the formation of structural compounds such as Mg 2 Al 4 , Mg 2 SiO 4 , Mg 2 Ca, and Ca 2 Mg 4 Zn 13 in the stir zone. The morphological study revealed plenty of white-grey (ESP) and dark grey (Si 3 N 4) sub-micron precipitates uniformly dispersed into the AZ31B matrix alloy. The EBSD map exhibited an average grain size of 2.95 ± 1.83 μm. The ultimate tensile stress at one, two and three successive tool-passes were found to be 357 MPa, 366.5 MPa and 375.4 MPa, respectively, which was comparatively 20–25% higher than the base alloy. The FESEM images of the fractured surface exhibited ductile striations and tear ridges with flat shear bands mixed with brittle fracture. The lowest COF obtained in this study was 0.29 for three too-passes at an average frictional force (Fx) of 2.17 N with a volumetric wear loss of 0.0769 mm3. • Multi-pass FSP of AZ31B alloy to overcome the challenges associated with the less hexagonal structure. • Utilization of waste chicken eggshell in a useful reinforcement to enhance the mechanical and tribological properties. • Microstructural changes and grain refinement analysis has been done through FESEM and EBSD analysis. • Tensile behavior with (DIC) images and fractographic analysis. • Tribological characteristics supported with 2D and 3D wear track analysis through surface profilometry. [ABSTRACT FROM AUTHOR]