Researchers introduced the CuO nanoparticles into the A356 melt through a two-stage stir-casting process. The particles underwent an in-situ metallothermic reaction with the molten aluminum, allowing a single addition to influence both the primary grain structure and the morphology of eutectic silicon. The authors framed the work around a long-standing limitation of cast A356 alloy: conventional methods do not readily achieve grain refinement and eutectic-silicon modification at the same time. The experiment used conventional casting equipment to test whether one nanoparticle addition could provide that dual control under laboratory conditions.

The as-cast structure and reaction products were examined using optical microscopy, scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy. These analyses showed the replacement of coarse columnar dendritic morphology by equiaxed α-Al grains and the conversion of acicular silicon plates into a fine eutectic silicon network. Mechanical testing produced a corresponding rise in Vickers microhardness from 54.8 ± 1.0 HV in the baseline alloy to 61.5 ± 2.1 HV after the CuO treatment. Thermal expansion was assessed with a dilatometer; the reported coefficient was approximately 25% below the rule-of-mixtures prediction, rather than 25% lower than the untreated alloy. The results therefore connect the altered microstructure with higher measured hardness and reduced thermal expansion within the tested material and processing conditions.

The largest reported functional change occurred in dry sliding wear tests conducted with a pin-on-disk tribometer, a hardened-steel counterface, and applied loads of 20, 40, and 60 N. The treated alloy reached a wear rate of 1.57 × 10−4 mm³/N m, representing an approximately 49% decrease, while its friction coefficient fell from 0.85 to 0.68. Surface examination showed a shift in the dominant wear mechanism from severe adhesive delamination toward abrasion-dominated wear. Taken together, the study reports that a single in-situ CuO nanoparticle addition can refine primary aluminum grains and modify eutectic silicon while improving microhardness, dimensional stability as reflected by reduced thermal expansion, and resistance to dry sliding wear. The evidence remains specific to A356 alloy, the two-stage stir-casting route, the tested nanoparticle additions, and the specified laboratory test conditions.

Subject of Research: Experimental CuO nanoparticle modification of microstructure and properties in cast A356 aluminum alloy

Article Title: Simultaneous grain refinement and eutectic silicon modification in A356 alloy via in-situ reaction with CuO nanoparticles

Article References: Ali, M., El-Taher, A. M., Amin, M., Soliman, H. N., & Gassour, H. (2026). Simultaneous grain refinement and eutectic silicon modification in A356 alloy via in-situ reaction with CuO nanoparticles. Journal of Materials Science, 61(41), 32140-32158. https://doi.org/10.1007/s10853-026-13679-8

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13679-8

Keywords: A356 aluminum alloy, CuO nanoparticles, grain refinement, eutectic silicon, stir casting, microhardness, thermal expansion, dry sliding wear, tribology, in-situ reaction, Simultaneous, grain

The material at the heart of the study is LM26, a widely used aluminium casting alloy prized for its performance at elevated temperatures. By stirring graphite particles and fly ash into the molten alloy through a stir-casting route, the researchers produced a hybrid composite in which soft, self-lubricating graphite coexists with hard, inexpensive fly ash particles. This combination is attractive because graphite can form lubricating films at sliding interfaces while fly ash, a by-product of coal combustion, adds hardness at almost no material cost. The catch is that the final properties of such composites depend heavily on the microstructure of the aluminium matrix, and that microstructure can be deliberately reshaped through heat treatment.

Solution treatment works by heating the alloy to a temperature high enough to dissolve brittle intermetallic phases into the matrix, holding it there to homogenize the structure, and then cooling at a controlled rate to lock in a supersaturated solid solution. The temperature chosen determines how much of the second phase dissolves, the holding time governs how completely that dissolution proceeds, and the cooling method dictates whether dissolved elements remain in solution or precipitate out again. Each of these three levers can alter the hardness of the matrix, the strength of the bond between matrix and reinforcement, and ultimately the way the composite behaves when its surface slides against a counterbody.

To map this three-dimensional parameter space efficiently, the team employed a Taguchi L27 orthogonal array, an experimental design that allows three factors at three levels each to be evaluated with just twenty-seven carefully chosen runs instead of a full factorial sweep. Solution treatment temperatures of 450, 500 and 550 degrees Celsius were paired with holding times of 2, 4 and 6 hours, and each combination was subjected to one of three cooling routes: slow furnace cooling, moderate air cooling or rapid water quenching. After treatment, every specimen was measured for hardness in Brinell numbers, tested for wear rate under dry sliding conditions, and characterized for its coefficient of friction, giving three response variables that often pull in different directions.

The measured values revealed a substantial spread across the treatment conditions. Hardness ranged from 42.3 to 51.2 Brinell hardness numbers, wear rates spanned 0.000667 to 0.000750 cubic millimetres per minute, and coefficients of friction fell between 0.4002 and 0.4501. These are not trivial differences for a component designer: a roughly twenty percent swing in hardness and a corresponding improvement in wear and friction performance can translate directly into longer service life and lower energy losses in sliding machinery. The results showed that as the heat treatment conditions were optimized, hardness climbed from its lowest to highest value while wear rate and friction simultaneously dropped, demonstrating that the three responses can be improved together rather than traded off against one another.

Because no single run was guaranteed to be best on all three counts at once, the researchers turned to TOPSIS, a multi-criteria decision-making technique that ranks each experimental condition by its relative closeness to an ideal solution, defined as the hypothetical condition with the best possible value for every response. The standout performer was Experiment 18, corresponding to a solution treatment at 500 degrees Celsius, a 6-hour hold and water quenching, which achieved the highest relative closeness value of 0.8933. This combination came closest to the ideal balance of maximum hardness with minimum wear and friction among all twenty-seven tested conditions.

Factor-level analysis, which averages the response across all runs containing a given parameter level, pointed to a slightly different optimum within the investigated design space: 550 degrees Celsius, 6 hours and water quenching, designated A3B3C3. The discrepancy between the single best run and the factor-level optimum illustrates a familiar feature of Taguchi analysis, where averaging effects can suggest combinations not directly tested. Both findings, however, converge on the same practical message: longer holding times and rapid water quenching favour the combined tribological response, while the temperature picture rewards careful selection within the studied range.

Analysis of variance added quantitative weight to these observations by partitioning the influence of each parameter on each response. Temperature emerged as the dominant factor for wear rate, coefficient of friction and the overall TOPSIS grade, meaning that the dissolution behaviour of the aluminium matrix during solution treatment exerts the strongest control over how the composite wears and slides. Cooling method, by contrast, had the greatest influence on hardness, consistent with the idea that quenching rate determines how much dissolved solute is retained in solution and how fine the resulting structure becomes. Holding time contributed across all responses but generally played a supporting role to temperature and cooling rate.

Scanning electron microscopy provided the microstructural context for these numbers, allowing the researchers to examine how the graphite and fly ash particles were distributed within the aluminium matrix. A reasonably uniform dispersion of reinforcements is essential for consistent tribological behaviour, since clustered particles can act as stress concentrators and debris sources during sliding, while well-distributed graphite can continuously replenish lubricating films at the wear surface. The microscopy work tied the macroscopic wear and friction measurements back to the underlying structure of the composite, reinforcing the link between heat treatment, microstructure and performance.

The broader significance of the study lies in its demonstration that post-casting heat treatment is not an afterthought for hybrid aluminium matrix composites but a primary design variable. For industries seeking to substitute lightweight composites for heavier ferrous components in engines and braking systems, the ability to dial in wear and friction performance through a documented treatment recipe, validated by a transparent Taguchi-TOPSIS workflow, offers a practical path from laboratory material to engineering component. The findings also highlight the value of fly ash, an industrial waste stream, as a functional reinforcement, aligning improved tribological performance with lower material cost and a measure of environmental benefit.

Subject of Research: Heat treatment optimization of LM26/graphite/fly ash hybrid aluminium matrix composites for tribological performance

Article Title: Effect of Heat treatment parameters on the tribological performance of LM26/graphite/fly ash hybrid aluminium matrix composites using Taguchi-TOPSIS optimization

Article References: Chellamuthu, P., Angappan, P., Duraisamy, P., Agarwal, A., & Dorji, K. (2026). Effect of Heat treatment parameters on the tribological performance of LM26/graphite/fly ash hybrid aluminium matrix composites using Taguchi-TOPSIS optimization. PLOS One, 21(10), e0360156. https://doi.org/10.1371/journal.pone.0360156

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0360156

Keywords: aluminium matrix composites, LM26 alloy, graphite, fly ash, heat treatment, solution treatment, Taguchi method, TOPSIS, tribology, wear rate, coefficient of friction, stir casting

The choice of matrix alloy was deliberate. AA6061 is a wrought aluminium alloy prized for its excellent thermal and physical properties, its corrosion resistance, and the ease with which it can be fabricated into machine parts, structural elements and aerospace components. Yet like most commercial alloys, it has limits in strength and wear performance that can restrict its use in demanding tribological applications such as brakes, bearings and gears. Materials scientists have long explored ways to tailor aluminium by adding hard ceramic or mineral particles, including silicon carbide, alumina, fly ash, red mud and zircon silicate, and previous studies have generally found that such reinforcements boost hardness and strength while often reducing density. What makes the new work distinctive is the use of marble dust, an abundant industrial waste stream from Rajasthan’s stone industry, which turns a disposal problem into a feedstock for advanced materials.

To create the composites, the team used a semi-automatic stir-casting process, one of the most economical and widely adopted liquid-state fabrication routes for metal matrix composites. Cleaned and cut AA6061 alloy rods were melted in a graphite crucible at 720 degrees Celsius, and the molten metal was fluxed to remove impurities. Around 2 weight percent of magnesium, added in the form of MgO, was stirred into the melt to improve wettability, a critical step because poorly wetted particles tend to cluster rather than disperse. Meanwhile, the marble dust was preheated to about 400 degrees Celsius for half an hour to drive off moisture and lower the surface energy of the particles, which further promotes uniform mixing. The heated reinforcement was then added incrementally while a graphite stirrer agitated the melt at 250 revolutions per minute for five minutes. The melt was superheated slightly to maintain fluidity and poured into a permanent mould, producing cast plates from which standard test specimens were machined.

Five compositions were prepared, spanning 0 to 6 weight percent marble dust in 1.5 percent increments, labelled M0 through M6. The researchers evaluated density, void content, tensile strength, flexural strength, hardness and impact strength for each formulation. A clear trend emerged: as the marble dust content increased, the void fraction dropped from roughly 12.5 percent to 6.66 percent, while every measured mechanical property improved. Tensile strength rose from about 238 megapascals in the unreinforced alloy to roughly 277 megapascals at 6 percent reinforcement. Hardness climbed from 75 to 90 on the Rockwell B scale, flexural strength increased from 180 to about 205 megapascals, and impact strength grew from 16.5 to 21 kilojoules per square metre. The team attributes these gains to two mechanisms: the rising dislocation density and the build-up of a stronger matrix-particle interface, which reduces voids and improves load transfer, and the ability of hard particles to act as barriers to dislocation motion, producing classic dispersion strengthening.

The tribological behaviour of the composites was assessed under dry sliding conditions, with the specific wear rate ranging from about 2.006 to 2.528 times ten to the minus six cubic millimetres per newton-metre. Three operating variables were systematically varied: normal load from 10 to 50 newtons, sliding distance from 800 to 4000 metres, and sliding velocity from 1 to 2 metres per second. Across the composition range, wear rate and friction coefficient increased with each of these parameters but fell as marble content rose. The M6 composite, containing the maximum 6 weight percent reinforcement, consistently delivered the lowest wear and friction. The researchers explain this through the same microstructural logic that governs the mechanical results: fewer voids mean a more continuous, better-bonded material that transfers load efficiently between matrix and particles, so the surface resists softening, ploughing and debris generation during sliding.

Scanning electron microscopy of the worn surfaces revealed the underlying wear mechanisms in vivid detail. At the lowest load of 10 newtons, the M6 composite displayed clean primary surfaces with minimal debris, evidence of its intactness and strength. At 20 newtons, mild ploughing and pitting appeared, and by 30 newtons deep ploughing grooves and a secondary layer of laminated wear debris became visible. At 40 and 50 newtons the damage turned aggressive, with massive debris layers and extensive pitting. The team attributes this escalation to rising interfacial temperatures at higher loads, which soften the surface, promote debonding and generate hard debris particles that then scour the interface in a destructive three-body abrasion mechanism. These micrographs directly link the macroscopic wear measurements to observable surface physics.

To optimise the sliding wear process, the researchers turned to Taguchi’s design of experiments, arranging trials in an L25 orthogonal array and using signal-to-noise ratios with a smaller-the-better objective to minimise wear. Analysis of variance on the results showed that normal load was the most influential parameter, contributing 33.33 percent of the variability in specific wear rate, followed by sliding distance at 13.36 percent, reinforcement content at 12.98 percent and sliding velocity at 9.64 percent. The highest F-value, 2.49 for normal load, confirmed its dominant role. The optimal parameter combination produced a signal-to-noise ratio of 58.60 decibels, and a confirmation experiment run at randomly selected settings validated the model with an error of only 3.6 percent, demonstrating that Taguchi’s approach can reliably guide wear-minimising process design for these materials.

Perhaps the most novel element of the study is its use of hybrid multi-criteria decision-making techniques to rank the five composites across all their performance metrics simultaneously. The two-phase AHP-TOPSIS algorithm first converts expert judgment about the relative importance of criteria into quantitative weights using Saaty’s nine-point scale, checking consistency to ensure the weights are trustworthy, and then measures each alternative’s closeness to an ideal solution. The hybrid AHP-R method follows the same first phase but uses reciprocal rank-based weighting in the second. In both analyses, the criteria hierarchy placed hardness, tensile strength, flexural strength and impact strength at the top, with density and wear rate weighted lower, and the consistency ratio of roughly 0.0044 fell far below the accepted 10 percent threshold. Critically, the two independent ranking methods converged on exactly the same order: M6 outperformed M4.5, which beat M3, with M1.5 and M0 trailing, confirming the subjective assessment that the highest marble content is optimal.

The convergence of experimental measurement, statistical optimisation and decision theory gives the findings unusual robustness, and the practical implications are considerable. The authors suggest that composites with low void content and strong mechanical properties are well suited to tribological applications, and that these marble-dust-reinforced aluminium alloys could serve as substitute materials in rollers, brakes, guideways, bearings and gears. Because the reinforcement is essentially industrial waste, the cost and environmental footprint of producing the composites should be far lower than those of conventional ceramic-reinforced alternatives. The work also adds to a growing body of literature showing that hybrid decision-making algorithms such as AHP-TOPSIS and AHP-R, borrowed from operations research, can rapidly and objectively rank material alternatives, sparing engineers from grappling with conflicting criteria by intuition alone.

The study was conducted with support from the Advanced Research Lab for Tribology and the Material Research Centre at Malaviya National Institute of Technology Jaipur, and the authors report no competing interests. While the research remains at the laboratory scale, the combination of a cheap, abundant reinforcement, a scalable casting process and statistically validated performance gains suggests a credible pathway from quarry waste to engineered components. For industries under pressure to cut both costs and carbon, the message of this work is striking: the material of the future for lightweight, wear-resistant metal parts may already be piling up in the dust of India’s marble workshops, waiting to be stirred into the melt.

Subject of Research: Marble dust particle-reinforced AA6061 aluminium matrix composites evaluated for mechanical strength and sliding wear performance using hybrid decision-making techniques

Article Title: Mechanical and sliding wear performance analysis of AA6061 − marble particulates reinforced alloy composites via hybrid decision-making techniques

Article References: Kumar, A., & Kumar, M. (2026). Mechanical and sliding wear performance analysis of AA6061 − marble particulates reinforced alloy composites via hybrid decision-making techniques. Journal of Materials Science: Metallurgy, 1(1), Article 15. https://doi.org/10.1007/s44492-026-00015-z

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00015-z

Keywords: AA6061 alloy, marble dust particulates, metal matrix composites, stir casting, sliding wear, mechanical properties, Taguchi method, ANOVA, hybrid AHP-TOPSIS, AHP-R method, tribology, automotive materials