PRODUCTION OF ALUMITE SUBSTRATE FOR HIGH-DENSITY MAGNETIC RECORDING MATERIAL

摘要

PURPOSE:To obtain an alumite substrate which is free from a black spot and cracking during heating and has remarkably improved film hardness in the stage of using a chromic acid soln. and subjecting the substrate to an alumite treatment by a constant voltage method by treating the substrate with the voltage higher than an ordinarily practised electrolytic voltage thereby forming the chemically converted film to a thickness exceeding 10mum. CONSTITUTION:An aluminum or aluminum alloy material is subjected to an electrolytic treatment with a voltage between preferably 70-100V by using a chromic acid soln. having 1.5-15% concn. by weight, thereby forming an alumite film on the surface of the material. The surface layer part of said film is polished away so that the film has a final thickness exceeding 10mum. The voltage is made higher than 40V of a Butherd method. The hardness of the chemically converted alumite film increases with an increase in the film thickness and when the film thickness exceeds 10mum (after polishing), the hardness attains 300Hv (Vickers hardness).