| 摘要 |
PROBLEM TO BE SOLVED: To actualize crystal grains in the material while its appearance is satisfactorily retained by subjecting aluminum or an aluminum alloy in which the average crystal grain size is controlled to the value equal to or above the specified one to immersing treatment for a specified time in an alkaline aq. soln. contg. zinc ions at a specified concn., and in which soln. temp. and pH are held to the specified ones. SOLUTION: An aluminum material (aluminum or an aluminum alloy) of >=1 mm average crystal grain size is immersed into an alkaline aq. soln. contg. zinc ions of 15 to 2,500 ppm concn., and in which soln. temp. is controlled to 40 to 60 deg.C, and pH is controlled to >=12 for 5 to 60 min. The surface part in accordance with the crystal orientation of the aluminum material is deposited with an optimum amt. of zinc thin film, and the surface is controlled to the one suitable for the revelation of a crystal grain pattern. The aluminum material can be obtd., e.g. by subjecting an aluminum material having >=99.5% purity to perfect softening of executing heating at 450 to 550 deg.C for >=3 hr, thereafter applying plastic deformation of about 1 to 10% thereto and executing heating at 550 to 650 deg.C for >=2 hr. The product high in designing properties can be obtd.
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