CuO Nanoparticles Refine Grains and Modify Silicon in A356 Alloy

Adding 0.5 to 1.5 weight percent of copper oxide nanoparticles to molten A356 aluminum alloy produced two simultaneous microstructural changes in a laboratory casting study: coarse columnar dendrites were replaced by fully equiaxed primary α-Al grains, and brittle acicular eutectic silicon plates became a fine, fibrous network. The treatment also increased Vickers microhardness by 12.2%, reduced the coefficient of thermal expansion to approximately 25% below a rule-of-mixtures prediction, and substantially improved dry sliding wear behavior. These findings come from experimental alloy casting and property testing, not from field trials or service applications.

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