ALUMINUM ALLOY SHEET MATERIAL FOR TRANSPORTATION- RELATED STRUCTURE SUPERIOR IN COATING PROPERTY AND PRESS FORMABILITY

摘要

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet material for a transportation-related structure, having required strength, superior coating properties and press formability. ;SOLUTION: The Al alloy sheet material includes 0.07-0.18 mass% (hereafter %) Si, 4.35-4.75% Mg, 0.05-0.15% Cu, 0.07-0.35% Fe, 0.25-0.45% Mn, 0.02-0.05% Cr, 0.001-0.1% Ti, 0.0005% or less Na, 0.0010% or less Ca, and the balance Al with unavoidable impurities. The material is characterized in that a mean crystal particle diameter measured in a sheet thickness direction is 10 μm or less in a surface part, and is 1.2 times or larger in a central part than in the surface part. Thereby, the sheet material has the necessary strength for the structure, and does not cause crack and the like in a manufacturing and forming process because of including appropriate contents of Si, Mg, Cu, Fe, Mn, Cr, and Ti, and controlling Na and Ca contents low, has superior coating properties because of making the crystals in the surface part moderately fined down, and consequently of not causing rough surface on a bent part, and in addition, has a superior press formability because the crystal particle diameter in the central part is greater than in the surface part, and consequently because difference between load stresses in the surface part and in the central part is alleviated.;COPYRIGHT: (C)2003,JPO