ALUMINUM SURFACE TREATED MATERIAL EXCELLENT IN WATER REPELLENT PROPERTY AND ITS PRODUCTION

PROBLEM TO BE SOLVED: To improve the heat transfer efficiency of the subject material by roughening the surface of an Al material to a high order pit structure in which small pits have been formed in a pit and moreover forming a water repellent film composed of an organosilane compd. or an organohalosilane compd. having a fluoroalkyl group thereon. SOLUTION: In 1st pits 4 of a prescribed depth formed on the surface of an Al material 2, pits are successively formed on each inside from large pits to small pits so as to form 2nd pits 6. This high order pit structure is formed on the surface to be imparted with water repellent properties, by which effective surface roughening is executed. The 1st and 2nd pits 4 and 6 preferably have the pit sizes of 0.1 to 10 μm. As to the surface roughening treatment for obtaining the high order pit structure, preferably, electrolytic etching in which the pits having relatively large pit sizes are formed is executed, and, after that, anodic oxidation is executed.