Nanoindentation responses of black anodic coating on additively manufactured Al-10Si-Mg alloy

The present work reveals the variation of nanomechanical properties (nanohardness-H and modulus-E) of black anodic coating on additively manufactured Al-10Si-Mg alloy. The plan-section of the coating has mud-crack-like morphology with various nano/micro-pores, micro-channels, and irregularities. In contrast, the cross-section possesses a compact morphology with minimum surface/sub-surface defects like micro-cracks or irregularities. The H and E are derived from nanoindentation experiments using Berkovich tip at loads 10-50 mN. The nanomechanical properties are higher across the cross-section than the plan section of the coating, attributing to the difference in morphology between the plan- and the cross-sections. Due to characteristic porosities, defects, and nano/micro-cracks in the anodic coating, Weibull statistical analysis has been employed to rationalize the scatter in nanoindentation-based data. For both plan and cross-sections, the H and E values decrease as the indentation load increases from 10 to 50 mN, confirming the indentation size effect (ISE). The well-established Meyer's law, Hays-Kendall approach, elastic recovery model, proportional specimen resistance (PSR) model and the modified PSR model have been used to thoroughly analyze the ISE characteristics.