the influence of friction stir processing on microstructure and tribological behavior of si3n4-reinforced 5083 aluminum alloy

Aluminum and its alloys have garnered significant attention in various industries due to their unique properties, such as a high strength-to-weight ratio and good formability. al5083 alloy, exhibits acceptable corrosion resistance in marine environments. however, it often falls in short terms service life because of its low hardness and wear resistance. to address these limitations, different methods, including coatings (electroplating, anodizing, plasma spraying, etc.), structural phase modification using lasers, and composite formation, have been explored to enhance the surface properties of this alloys. surface composite fabrication, aiming to improve the tribological behavior of al5083 alloy, presents a crucial challenge in component production. friction stir processing (fsp) is one of such method that enhances surface properties by using a movable pin tool on aluminum surfaces containing reinforcing particles. the aim of this study was to investigate the effect of fsp on microstructure and tribological behavior of al5083 alloy reinforced by si3n4 particles. characterization of the samples involved microstructure examinations (optical and scanning electron microscopy), chemical composition assessment (energy-dispersive x-ray spectroscopy), and phase analysis (x-ray diffraction). results showed that the fsp process without reinforcing particles led to surface grain refinement due to dynamic recrystallization within the stirring zone. the aluminum grains that were originally elongated in the rolling direction and contained al3mg2 precipitates were completely transformed into a well-aligned, significantly smaller size in the disturbed region. another notable outcome of the fsp process was the refinement and better dispersion of the precipitates within the aluminum matrix. moreover, the presence of reinforcing particles resulted in the formation of highly refined al/si3n4 surface composites. xrd patterns of fsped samples exhibited distinct preferred orientations compared to the substrate, but there was no change in the existing phases and no new intermetallic phase formation. microhardness measurements revealed increased hardness in the stirring zone (99 hv) in presence of si3n4 particles compared to the base metal (74 hv) and the fsped sample (85hv) without reinforcing particles showed the most significant improvement. mechanisms for enhancing the hardness of composite specimen include the following: (1) according to the hall-petch relationship, hardness increases in the disrupted region due to grain refinement. (2) orowan mechanisms prevent dislocation motion by scattering ceramic particles and impeding plastic deformation. (3) grain boundary pinning occurs through the uniform distribution of strengthening particles, which act as grain growth inhibitors. (4) a disparity in thermal expansion coefficients between the al5083 matrix and the reinforcing material leads to increased dislocation density and the stapling in the joints and ultimately hardness enhancement. tribological behavior was assessed using reciprocating wear tests, revealing significant fluctuations in friction coefficients for all samples. repeated attachment and detachment of abrasive particles along the wear path led to the formation of irregularities. consequently, as the pin gets trapped behind the particles and then released, it causes fluctuations in the contact force between the pin and the sample's surface. ultimately, this results in significant variations in the friction coefficient. nevertheless, the composite sample exhibited the lowest average friction coefficient (μs = 0.25), attributed to the presence of si3n4 particles facilitating sliding and higher hardness. in addition to its outstanding anti-friction properties, the produced composite displayed remarkably high hardness, resulting in minimal weight loss due to its superior ability to withstand against abrasive forces. the analysis of the wear mechanism in the samples was conducted using sem images and eds data of the worn surfaces. the predominant wear mechanisms observed to be adhesive, abrasive, and delamination for the substrate, fsped, and composite samples, respectively.aluminum and its alloys have garnered significant attention in various industries due to their unique properties, such as a high strength-to-weight ratio and good formability. al5083 alloy, exhibits acceptable corrosion resistance in marine environments. however, it often falls in short terms service life because of its low hardness and wear resistance. to address these limitations, different methods, including coatings (electroplating, anodizing, plasma spraying, etc.), structural phase modification using lasers, and composite formation, have been explored to enhance the surface properties of this alloys. surface composite fabrication, aiming to improve the tribological behavior of al5083 alloy, presents a crucial challenge in component production. friction stir processing (fsp) is one of such method that enhances surface properties by using a movable pin tool on aluminum surfaces containing reinforcing particles. the aim of this study was to investigate the effect of fsp on microstructure and tribological behavior of al5083 alloy reinforced by si3n4 particles. characterization of the samples involved microstructure examinations (optical and scanning electron microscopy), chemical composition assessment (energy-dispersive x-ray spectroscopy), and phase analysis (x-ray diffraction). results showed that the fsp process without reinforcing particles led to surface grain refinement due to dynamic recrystallization within the stirring zone. the aluminum grains that were originally elongated in the rolling direction and contained al3mg2 precipitates were completely transformed into a well-aligned, significantly smaller size in the disturbed region. another notable outcome of the fsp process was the refinement and better dispersion of the precipitates within the aluminum matrix. moreover, the presence of reinforcing particles resulted in the formation of highly refined al/si3n4 surface composites. xrd patterns of fsped samples exhibited distinct preferred orientations compared to the substrate, but there was no change in the existing phases and no new intermetallic phase formation. microhardness measurements revealed increased hardness in the stirring zone (99 hv) in presence of si3n4 particles compared to the base metal (74 hv) and the fsped sample (85hv) without reinforcing particles showed the most significant improvement. mechanisms for enhancing the hardness of composite specimen include the following: (1) according to the hall-petch relationship, hardness increases in the disrupted region due to grain refinement. (2) orowan mechanisms prevent dislocation motion by scattering ceramic particles and impeding plastic deformation. (3) grain boundary pinning occurs through the uniform distribution of strengthening particles, which act as grain growth inhibitors. (4) a disparity in thermal expansion coefficients between the al5083 matrix and the reinforcing material leads to increased dislocation density and the stapling in the joints and ultimately hardness enhancement. tribological behavior was assessed using reciprocating wear tests, revealing significant fluctuations in friction coefficients for all samples. repeated attachment and detachment of abrasive particles along the wear path led to the formation of irregularities. consequently, as the pin gets trapped behind the particles and then released, it causes fluctuations in the contact force between the pin and the sample's surface. ultimately, this results in significant variations in the friction coefficient. nevertheless, the composite sample exhibited the lowest average friction coefficient (μs = 0.25), attributed to the presence of si3n4 particles facilitating sliding and higher hardness. in addition to its outstanding anti-friction properties, the produced composite displayed remarkably high hardness, resulting in minimal weight loss due to its superior ability to withstand against abrasive forces. the analysis of the wear mechanism in the samples was conducted using sem images and eds data of the worn surfaces. the predominant wear mechanisms observed to be adhesive, abrasive, and delamination for the substrate, fsped, andcomposite samples, respectively.