Impact of Al2O3 particles on the hardness, metallurgical and corrosion behaviour of Al 6061–10 wt. % Al2O3 functionally graded composite

The objective of this work is to create a hollow cylindrical Aluminium (Al) 6061 alloy reinforced with 10 wt% Alumina (Al 2 O 3 ) Functionally Graded Composite (Al 6061–10 wt% Al 2 O 3 FGC) using horizontal centrifugal casting. Vickers microhardness testing revealed a maximum hardness of 108 HV at the Al 2 O 3 -rich exterior periphery, which is 76% higher than the Al 2 O 3 -depleted interior region. Optical microstructural and XRD (X-ray Diffraction) analysis confirmed the gradient distribution of Al 2 O 3 particles. Acidic immersion corrosion studies on the Al 2 O 3 -rich region were performed using Sulphuric acid (H 2 SO 4 ), Hydrochloric acid (HCl), and Nitric acid (HNO 3 ) solutions for immersion durations up to 216 h. The highest Corrosion Rate (CR) (27.31 mm/yr) was observed in HCl at 72 h due to Chloride (Cl) ion attack and pitting, while the lowest CR (6.83 mm/yr) occurred in HNO 3 at 216 h owing to stable oxide film formation. Taguchi’s Signal-to-Noise Ratio (SNR) analysis indicated immersion duration as the most significant factor, with Analysis of Variance (ANOVA) confirming its 56.25% contribution to CR variation. High Resolution Scanning Electron Microscopy (HRSEM) analysis of corroded surfaces showed microcracks, interfacial regions, and surface damage. The findings highlight that controlling immersion duration and selecting appropriate acidic media can significantly enhance the corrosion resistance of Al 2 O 3 -reinforced Al 6061 FGCs, making them suitable for chemical industry applications.