Mechanical properties at nanometric scale of alumina layers formed in sulphuric acid anodizing under burning conditions

A mechanical study (hardness, H and Young's modulus, E) at nanometric scale of the distribution of mechanical properties across the surface of porous anodic alumina (PAA) films formed during aluminium anodizing in sulphuric acid under burning conditions is presented. Statistical methods have been employed to extract the mechanical properties of the protruding oxide structures (POS) observed in the burning areas and the results have been compared with those obtained from the standard PAA (S-PAA) of the non-burning areas. The results indicated that H and E of the POS are 3.8 ± 0.3 and 80 ± 4 GPa, respectively, while those of the S-PAA are 6.8 ± 0.5 and 125 ± 8 GPa. Thus, the hardness and Young's modulus of POS are factors of about 1.6–1.8 times lower than those of S-PAA, indicating that POS have lower mechanical properties associated with their different chemical composition and structure.