Characteristics and tribological behavior of the hard anodized 6061-T6 Al alloy.

The hard anodizing process is one of the best choices to achieve high wear resistance in a 6061-Al alloy, which is commonly used in marine and aerospace applications. In this study, the hard anodizing process was performed by applying several current densities at different times. Two types of electrolytes containing various concentrations of sulfuric acid or oxalic acid were used as the bath. The microhardness of the coatings was measured. Morphology, thickness, and structure of the samples were investigated through a scanning electron microscope (SEM), and an X-ray diffractometer (XRD). Surface roughness and tribological behavior of the optimum samples were also examined. The results revealed that there was an optimum value for the electrolyte concentration, as well as the hard anodizing current density and time at which the hardest coating was obtained. All the oxide films had an amorphous structure. Doing the hard anodizing at 35 mA/cm2 in a sulfuric acid bath for 50 min resulted in a uniform and crack-free coating. The weight loss of this oxide film was 50 and 21 times lower than the substrate and the coating obtained in an oxalic acid bath at the optimum conditions, respectively. • Hard anodizing of 6061-T6 Al alloy in the sulfuric and oxalic acid baths. • Effect of electrolyte concentration, current density, and time on properties. • Sulfuric acid was better electrolyte than oxalic acid for hard-anodizing of 6061-Al. • All the hard-anodized films had higher hardness and wear resistance than base alloy. • Optimum condition to obtain compact, hard and wear resistant coating is proposed. [ABSTRACT FROM AUTHOR]