||Micro-arc oxidation (MAO) has been extensively applied in many fields such as aerospace, military industry, etc. MAO coatings outperform other traditional surface treatments (such as anodic treatment and electroplating) in terms of corrosion resistance and wear resistance. MAO is a more environmentally friendly process. During MAO, extremely high temperature of micro arc will lead to oxidation and sintering reaction and quenching on the anodic surface. Therefore, thermal stress and unique microstructure will be formed during MAO process. In the study, MAO coating was deposited on one side of aluminum foil used as substrate fixed in home-made holder. There are two kind most common electrolytic solutions, silicate and aluminate, accessed in this work. After MAO coating, the residual aluminum metal substrate will be stripped by aqueous NaOH(1.5M) solution. The detached MAO coating can be obtained. The internal stress of the detached silicate–containing MAO coating is around 20~40MPa and the attached aluminate-containing MAO coating is around 60~200MPa, determined from the radius of curvature of the detached MAO coatings. From the powder XRD of silicate-containing MAO coatings,γ-Al2O3, mullite and amorphous structure are found. The crystallinity of MAO coating will increase after annealing at 800℃ and 1200℃ treatment. DTA and TMA indicate that amorphous MAO will transform intoγ-Al2O3 aroundglass transition temperature, say 700℃. Subsequently, γ-Al2O3 will be further transformed toα-Al2O3 at 970℃. The activation energy of the transformation ,293kJ/mole, determined from DTA spectra using different heating rate. From TMA analysis, thermal expansion coefficient of silicate-containing MAO coating is 6.5910-6m/K. Aluminate-containing MAO coating consists ofα-Al2O3 and small amount of amorphous structure. From XRD and TMA analysis, amorphous phases transformed intoα-Al2O3 around 920℃,i.e. glass transition temperature. From TMA analysis, thermal expansion coefficient of aluminate-containing MAO coating is 8.2×10-6 /K.