Surface engineering approaches that simultaneously improve tribological, corrosion and fatigue performance are of significant interest for high-strength aluminum (Al) alloys used in aerospace applications. In this study, the effect of ultrasonic nanocrystal surface modification (UNSM) treatment load on the microstructural evolution, mechanical properties, tribological behavior, corrosion resistance and fatigue performance of Al7075-T6 alloy was systematically investigated. Surface integrity and microstructural changes induced by UNSM were characterized using electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and microhardness measurements. Tribological behavior was evaluated under dry reciprocating sliding conditions, while corrosion performance was assessed by potentiodynamic polarization testing in a 3.5 wt% NaCl solution. Fatigue behavior was examined using rotary bending fatigue (RBF) tests in the stress range of 200–400 MPa. The results demonstrate that UNSM treatment leads to significant grain refinement and the formation of a nanostructured surface layer accompanied by enhanced surface hardness and compressive residual stress. Consequently, the UNSM-treated samples exhibited markedly enhanced wear resistance, corrosion resistance and extended fatigue life compared to the untreated alloy. The underlying enhancement mechanisms are discussed based on surface morphology, wear track analysis, corrosion and fatigue behavior. These findings highlight the potential of UNSM treatment as an effective and scalable surface modification technique for improving the service performance of Al7075-T6 alloy for aerospace components.
The effects of Si content in the slurry (0–20 wt%) and heat-treatment temperature (900–1000 °C) on the microstructure, phase transformations, and oxide scale morphology of aluminide coatings produced by reactive air aluminizing (RAA) on IN939 superalloy were investigated. Experimental findings from XRD and SEM/EDS analyses were cross-validated with thermodynamic calculations. Si-free coatings developed a thick oxide scale with needle-like γ/θ-Al2O3 whiskers, exhibiting limited protectiveness due to high growth rates. In contrast, Si addition shifted the dominant growth mechanism from outward to inward growth, eliminating whiskers and promoting a thinner, denser, polyhedral oxide scale while significantly accelerating the γ/θ → α-Al2O3 transformation. Phase and thermodynamic analyses revealed that Si acts as a getter for Cr and Ti, forming stable CrxSiy and TiSi silicides that suppress Ti outward diffusion and prevent detrimental TiO2 formation, which otherwise stabilizes transient γ/θ-Al2O3, inhibiting α-Al2O3 formation. Thermodynamic calculations accurately predicted silicide stability, showing strong agreement with experimental observations. Ultimately, Si-modified coatings (≥10 wt% Si in slurry) enabled the formation of a protective α-Al2O3 scale with no detectable γ/θ phases across all temperatures investigated (900–1000 °C). These findings feature the critical role of Si as a microstructural modifier in the RAA process, offering a promising pathway for developing protective aluminide coatings at reduced temperatures.
