Mechanical and corrosion characteristics of grain refined ZA-27 alloy and ZA-27/Al2O3 nano-composite produced by ultrasonic cavitation technique

In this study, the physical, mechanical, and chemical characteristics of grain refined zinc-aluminum alloy (ZA-27) and ZA-27 based nano-composite reinforced with 1wt.%Al2O3 nanoparticles have been investigated. Ultrasonic cavitation technique was used to fabricate these materials, and they were examined using optical microscopy, micro-Vickers hardness tester, and potentiodynamic polarization. Scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) was used to investigate surface morphology and chemical elements of the specimens before and after corrosion testing to explain corrosion behaviors. ZA-27 alloy with fine equiaxed grains and 22 % porosity content with respect to the as-cast alloy was fabricated, resulting in a higher microhardness number. Potentiodynamic polarization test results revealed that it has better resistance for localized corrosion; the rapid dissolution of the zinc-rich phase presented in the interspacing region produces a salt layer quickly; this layer effectively protects the underlying metal surface from pits formation. The fabricated nano-composite has a porosity content of 54.2 % of the as-cast porosity content, and a smaller dendritic structure was formed with a uniform dispersion of the Al2O3 nanoparticles within the ZA-27 alloy matrix. Therefore, its microhardness number is greater than that of the as-cast alloy. The potentiodynamic polarization test analyses revealed that its uniform and localized corrosion resistance was improved. Micro-galvanic cells were formed between the primary and secondary phases in the small dendritic structure of the nano-composite, which improves its corrosion resistance.