The Al alloy material null for the air carrier which is superior in the water resistance and resistance thread rusted

摘要

PROBLEM TO BE SOLVED: To improve both filiform errosion resistance and water resistance of an Al alloy material by forming Al hydrated oxide film coposed of a planar upper layer film and a granular lower layer film having a specified thickness on the surface of an Al alloy material and providing the surface with a coating film other than cation electrodeposition cating film. ;SOLUTION: The surface of an Al alloy material 1 is provided with an Al hydrated oxide film 2 and a coating film 5 accompanied by no electrochemical reaction. The Al hydrated oxide film 2 is composed of a planar relatively coarse upper layer film 3 and a a granular relatively dense lower layer film 4. The film thickness of the lower layer film is controlled to 50 to 3000 Å. The coating film 5 is formed by the coating film accompanied by no electrochemical reaction such as spray coating of a middle coat 6 and a finish coat 7. The Al hydrated oxide film is expressed by Al₂O₃.XH₂O, and the upper layer film 3 is the the one of ≥2 X enough in hydration, in which the crystals of the planar Al hydrated oxides 9 are alternately piled up. The lower layer film 4 is the one of about 1 X, in which granular Al hydrated oxides 10 are crowded.;COPYRIGHT: (C)1999,JPO