In this study, in order to evaluate the adhesion properties of the hydroxide ˆlm formed on 6061 alloy (Al 1Mg 0.6Si (wt.%)) sheets prepared by steam coating, we examined the microstructure and cracking behavior of hydroxide ˆlm on Al alloy sheets prepared by steam coating at 220°C for 24 h. EBSD analyses revealed the steamcoated sample exhibits microstructure of a Al matrix consisted of equiaxed grains with a mean grain size of approximately 20 mm. The studied sample exhibits high hardness

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... 79 HV due to the strengthening by the precipitates of nanoscale particles (Mg 2 Si). The observation for the surface morphologies revealed the hydroxide ˆlm consisted of a number of particles with a mean size of approximately 300 nm and cross-sectional microstructural observations identiˆed a continuous hydroxide ˆlm with a thickness of approximately 1.2 mm. The XRD measurement demonstrated the formed hydroxide ˆlm consisted of the g AlO(OH) phase. Minute microstructure analyses revealed that the hydroxide ˆlm exhibits a dual layer structure consisting of g AlO(OH) crystalline layer on the surface and a continuous Al rich layer on the Al alloy. The cracking and delamination behavior of the hydroxide ˆlm were examined by bending test. It was found that the local delamination of g AlO(OH) phase would occur under compressive stress rather than tensile stress, whereas the delamination of the hydroxide ˆlm from the Al alloy substrate was not observed. These results indicate that the hydroxide ˆlm prepared by steam coating has a remarkable adhesion strength on the Al alloy substrate.