High-strength aluminum alloy plate and process for producing the same

Abstract

The invention provides a high-strength aluminum alloy plate which is suitable for use as structural materials such as ones for domestic electrical appliances and exterior automotive sheets and combines excellent unsusceptibility to surface roughening and formability; and a process for producing the plate. The high-strength aluminum alloy plate has a chemical composition containing 2.0-3.3 mass% Mg, 0.1-0.5 mass% Mn, and 0.2-1.0 mass% Fe, the remainder being unavoidable impurities and Al and the unavoidable impurities containing less than 0.20 mass% Si. In the plate, intermetallic compounds have an average diameter in terms of equivalent-circle diameter of 1 mum or smaller and an areal proportion of 1.2% or higher, recrystallized grains have an average grain diameter of 10 mum or smaller, and the tensile strength is 220 MPa or higher. An aluminum alloy melt having the chemical composition is poured into a twin-belt casting machine to continuously produce, by casting, a thin slab having a thickness of 6-15 mm at a cooling rate of 50-200 DEG C / sec as measured in a position corresponding to 1 / 4 the slab thickness. The cast is wound into a coil and then cold-rolled at a cold rolling reduction of 60-98%. The resultant plate is subjected to final annealing with a continuous annealing furnace in which the plate is heated at a rate of 100 DEG C / min or higher and held at a temperature of 400-520 DEG C for a period of 5 minutes or shorter to produce the high-strength aluminum alloy plate.

Description

technical field [0001] The present invention relates to high-strength aluminum alloy sheets requiring excellent surface roughening and formability suitable for home appliances and automotive exterior panels and other structural materials. Background technique [0002] Hitherto, cold-rolled steel sheets have been used for home appliances and automobile outer panels. Recently, however, due to demands for weight reduction, Al-Mg alloy sheets having high strength and excellent formability have been proposed. [0003] For example, Japanese Patent Laid-Open (A) No. 07-278716 proposes to limit the Mg content to 2.0-6.0% by mass, the Si content and the Fe content to 1.5% by mass or less, and continuously cast the melt to a slab thickness ( slab thickness) is 1-10 mm, and the cooling rate is 10° C. / second or higher in order to finely disperse the intermetallic compound in the matrix to obtain an aluminum alloy for forming with excellent mechanical properties. [0004] However, the ...

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Problems solved by technology

[0004] However, the above-mentioned documents describe the evaluation of the average precipitate size, mechanical properties and formability, but there is no description on the recrystallized grain size and surface roughness

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