| 摘要 |
PURPOSE:To obviate generation of a crack on the surface of an aluminum alloy substrate even if the substrate is heated to a high temp. by providing a thick heat resistant anodically oxidized film formed by a chromic acid electrolyte on the surface of said substrate. CONSTITUTION:An oxide film layer is provided on the surface of an aluminum alloy substrate by electrolyzing the substrate in an aq. contg. CrO3. The surface of such film having >=10mum film thickness does not crack even if the substrate is heated to >=250 deg.C. The preferable range of CrO3 concn. in the chromic acid electrolyte is 2-12%. The formation of a uniform film is difficult with the concn. except said range. The preferable range of CrO3 concn. in actuality is 3-10%. The burnt deposit of the film is liable to arise if the temp. of the chromic electrolyte is below 20 deg.C and the film is liable to dissolve excessively at the temp. over 70 deg.C. The preferable range in actuality is 25-60 deg.C.
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