Recently, cylinder liners of automotive and aircraft engines are encountered severe wear due to piston slap occurred by the repeated sliding stroke of piston. This research focuses on providing an alternative material for cylinder liners, which can be obtained through friction stir processing on AA7075 with different weight ratios of reinforcements like Al₂O₃ and SiC. Friction stir processing is executed with a tool rotational speed of 1000 r/min and traveling speed of 56 mm/min at 2° tool tilt angle. The images of optical microscopy reveal the fine-grains with a homogeneous distribution of secondary phase particles and also offer decrement in particle clustering except at some localized regions. It is identified that addition of 3.7 wt.% Al₂O₃ + 3.0 wt.% SiC in AA7075 enhanced the microhardness about 33.96% higher than base matrix. Hence, wear resistance of the specimen is improved. Dry sliding wear behavior of specimens is analyzed using pin on disc at 20, 40, and 60 N load conditions to create the actual sliding behavior of piston on cylinder wall. Increasing the wt.% of Al₂O₃ particles enhanced the wear resistance of AA7075 surface hybrid composites at 20 N load due to the formation of protective tribofilm. Specimen with 3.7% Al₂O₃ + 3.0% SiC has better lubrication and load-bearing capacity that exhibits superior tribological behavior at 40 and 60 N. Higher Fe content of 5.44 wt.% has been obtained through spectroscopy analysis in S₅, which is 8% and 6% higher than S₃ (7.5% of Al₂O₃) and S₇ (6% of SiC), respectively. The scratching action of this hard specimen on the counterpart brings more Fe content. Increase of Al₂O₃ particles paved the way for tribofilm formation and identified through scanning electron microscopy micrographs. The observation from worn specimens shows that finer wear debris had increased by adding more quantity of SiC particles due to abrasive wear mechanism.

In recent years, Aluminium Alloy 7075 plays a vital role in the manufacturing of aircraft wing and fuselage skin due to its light weight and specific strength characteristic behavior. The components like aircraft wing and fuselage skin faces serious erosion issues due to sand particles while high speed running conditions. This issue is focused into the present research and fabrication of AA7075 Surface Hybrid Composites (SHCs) with reinforcements like Aluminium Oxide (Al₂O₃) and silicon carbide (SiC) through the novel Friction stir Processing (FSP) technique is suggested. Microhardness tests are performed for different combinations of dual reinforcement and the erosion resistance is evaluated for the specimen with superior microhardness value. This research aims particularly on evaluating the erosion performance of the aforementioned hard specimen. Input erosion parameters like jet distance, jet pressure, jet angle, erodent impinging time and mesh number of erodent are considered and they are optimized through Taguchi technique. The obtained result undergoes Analysis of Variance (ANOVA) test and each parameter based percentage contribution is identified. The surface morphology analysis shows that grain refinement and homogenous distribution of reinforcement particles are at less surface degradation when compared to base AA7075.

Aluminum alloy-based surface composites processed by friction stir processing with enhanced hardness and impact energy is potentially suitable for aircraft and automotive applications. This behavior is improved by applying design of experiments (DOEs) in finding the suitable combination of process parameters. The influence of tool rotational speed, transverse speed, tilt angle, plunging depth and number of passes on hardness and impact energy are determined via Taguchi. It is identified that No. of pass plays a major contribution based on ANOVA. Single optimal parameter obtained through TOPSIS is employed to fabricate the composites with different volume ratios of WO₃ and SiC particulates. Microstructural characterization of all the defect free surface composites depicts wide and homogenous dispersion of reinforcement particulates. Surface hybrid composite specimen comprising both WO₃ and SiC particles significantly raises the microhardness to 214VHN attributed to the homogenous dispersion strengthening and grain boundary pinning mechanism. The specimen tends to show enhanced impact energy (12.3 J) due to extensive load bearing capacity of the reinforcements.

High strength, minimum thermal and electrical conductivity are the major requirements of aircraft applications which could be obtained by micro-structural modifications of the composites with particulate reinforcements. The proposed work focus the analysis on the behavior of micro hardness, coefficient of thermal expansion, thermal and electrical conductivity of AA7075 fabricated by friction stir processing with different weight ratios of Al2O3 and SiC. Different surface hybrid composites are formed by varying the weight ratios. It ensures the formation of fine grained structure and decrease in thermal and electrical conductivity values with addition of higher hardness. During the friction stir processing, the working temperature is identified between 99.4 and 316.6ºC for the proposed composites, which shows 15.6% and 49.8% that of the melting point of AA7075 (635ºC). Experimental investigation on thermal conductivity and electrical conductivity has been conducted under different heat input values through varying the applied voltage from 25 to 225V. The observation shows surface hybrid composites depicts lower conductivity values with Al2O3 & SiC particles due to variation in energy level of electrons and phonons. Among the observations, the specimen S5 reinforced with equal weight ratios of Al2O3 and SiC yields the maximum micro-hardness of about 265VHN and lower coefficient of thermal expansion of about 13µm/mºC. This is due to the reinforcement behavior and formation of Al4C3 intermetallics. The morphological analysis also supports the requirements of aircraft components.

The novel friction stir technology is adopted in modern automotive industries to meet the desired properties like hardness, impact toughness and tribological behaviour over the conventional techniques like stir casting, compo casting, squeeze casting, electroplating and infiltration methods. AA7075 surface composites fabricated with different volume fractions of fly ash and emery particles is said to enhance the aforementioned properties. The composites are processed through friction stir process (rotational speed −1200 rpm, transverse speed – 56 mm/min, tool tilt angle – 2 °). During characterization, the Microstructural examination of surface composites depicts fine and homogenous distribution of reinforcements in the friction stir process region owing to severe plastic deformation and dynamic recrystallization process. Substantially, good interface is formed between the reinforcement particulates and base substrate. Inclusion of Fe₃O₄, Al₂O₃ and SiO₂ constituents through fly ash and emery reinforcements associated with the homogenous dispersion strengthening mechanism favours for the superior hardness of surface hybrid composite specimen 50E50FA. Decremented grain size and load bearing capacity of the reinforcements is beneficial for the crack propagation resistance that enhances the impact toughness behaviour (17.4 J/cm²) of the same specimen. Wear rate of the specimens are evaluated through pin on disc tribometer. The decrease in the wear rate of hard specimen 50E50FA is observed due to the reduced contact area between its surface and counter disc. The morphology of worn specimens using SEM analysis shows the combined abrasive and adhesive wear as the worn mechanism.

Superior wear resistance and a high level of tensile strength in piston ring materials are achieved using AA7075 surface composites (SCs) that are fabricated by reinforcing the steel slag (SS) particulates through proper selection of friction stir process (FSP) parameters using the multipass technique. The optical structure elucidates that fine and equi-axed grains are ascertained in the stir zone of the processed region, and by increasing the number of passes from one to three, a homogenous dispersion of particulates and a reduced grain size (9 µm) is obtained. In particular, a clear and defect-free interface is prominent on the resulting composite surface. Field emission – scanning electron microscopy (FESEM) identifies the dispersion of reinforcements, while X-ray diffraction (XRD) technique and energy dispersive spectroscopy (EDS) mapping confirm the existence of reinforcing elements. The Orowan strengthening effect and reduced oxygen content around the SiO ₂ and CaO elements in the three-pass FSP SC specimen tend to increase its load-bearing capacity and result in superior hardness (353.3 VHN) and tensile strength (792.6 MPa). However, the same specimen exhibits a reduced percentage (%) elongation due to multiplied fragmentation of reinforcements, which eventually restricts the plastic movement of the AA7075 matrix. The SEM fracture morphology indicates that failure occurred through a combination of ductile and brittle modes. Furthermore, the SC specimen with two passes prominently decreases the wear rate (333 × 10 ⁴ mm ³ /m), which can be attributed to the commendable trilayer formation, and the worn morphology indicates the abrasive wear was the dominant wear mechanism. This fabricated specimen with high-strength characteristics can be beneficial for design engineers. During piston ring design, an increased level of the factor of safety can be achieved.