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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]

Lightweight composite materials for potential thermal applications are the contemporary demand for manufacturing and aircraft industries where the possibility to improve and tailor the desired properties is based on the application. Carbonized eggshell powder is a solid lubricant with absorbent capability and has proven as a reinforcement for metallic base composites. In the present work, an attempt is made to investigate the effect of carbonized chicken eggshell powder (3 to 9% by weight) on the microstructural and thermal properties of Al7075 alloy processed by solid-state friction stir processing. An infrared thermography and three K-type thermocouples equipped with the base plate at three equal distances are used to measure the temperature with respect to time. The comparative study of microstructure and grain structure analysis has been done by light microscopy, scanning electron microscopy, and electron backscattered diffraction methods. The findings explored the dynamic recrystallization and grain recovery with a reduced grain size of 6.2 to 10.3 µm at a varying percentage of eggshell powder (3 to 9%) in the stir zone. The thermal conductivity and coefficient of thermal expansion (CTE) were measured for the temperature range of 50 to 400 °C. In addition to it, differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), and derivative thermo-gravimetric analysis (DTG) are conducted for the temperature range of 25 to 900 °C to discuss the endothermic, exothermic nature, and degradation characteristics. The result revealed the decreasing trend of thermal conductivity, and CTE values were found in the range of 97 to 53 W/mK and 26.6 to 24 × 10−6 K−1 (heating cycle), 27.2 to 23.8 × 10−6 K−1(cooling cycle), respectively. Furthermore, the higher and lower thermal conductivity of 108 W/mK and 62 W/mK is observed at higher and lower terminal voltages, 250 V and 100 V, respectively. The DTA, TGA, and DTG curves explored the maximum weight loss, which varies up to 5.25% with exothermic peaks and decomposition steps for each surface composite. [ABSTRACT FROM AUTHOR]

Lightweight and high strength materials are the primary requirements in the field of defense like in aircraft structures and aerospace applications. In this context, aluminum-based composites are one of the suitable choices because of its improved characteristics. In the present work, an attempt is made to develop aluminum (A359) based surface composites by incorporating the Si 3 N 4 particles through friction stir processing (FSP). The numbers of FSP tool passes (single, two and three) are considered as variable parameters to evaluate its effect on various characteristics. The microstructural examination has been carried out by optical microscope and surface morphological analysis was done by scanning electron microscopy images. EDS with mapping images are used to observe the phase distribution and to identify the elements of the alloying and reinforcement materials. The elemental presences are also validated by X-ray diffraction and Raman spectroscopy. Further, mechanical properties like tensile test supported by fracture analysis and Rockwell hardness profile of the FSP zone are also discussed. In addition to it, the present work also an emphasis on the effect of the number of FSP tool passes on its wear resistance and thermal expansion. The results revealed that the value of maximum tensile strength and hardness were found to be 576 MPa and 125 HRB respectively in single pass FSPed composite. However, if the number of passes is increased then the maximum wear loss (11.7 × 10−3 g), maximum expansion due to heat (9 mm3) is observed at three-pass of FSP tool. Image 1 • Development of novel A359/Si 3 N 4 surface composite produced by friction stir processing. • Microstructural, morphological and structural analysis of A359/Si 3 N 4 surface composite. • The effect of multiple tool passes on tensile strength and Rockwell hardness profile of FSP stir zone. • The effect of multiple tool passes on Wear loss with respect to sliding distance. • Thermal expansion test to discuss the behavior of developed composite at high temperature. [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]