Aluminum alloy sheet and method for manufacturing the same

Abstract

An aluminum alloy sheet is manufactured by preparing a slab having a thickness of 5 to 15 mm with a continuous casting machine by a continuous casting process using molten alloy containing following components: 0.40% to 0.65% of Mg, 0.50% to 0.75% of Si, 0.05% to 0.20% of Cr, and 0.10% to 0.40% of Fe, remainder being Al, the components being essential elements, and optionally up to 0.15% Cu, 0.10% Ti; winding the slab into a coil; hot-rolling or directly coiling up the slab; cold-rolling the slab into a sheet; subjecting the sheet to solution heat treatment with a continuous annealing furnace; and then pre-aging the sheet. The aluminum alloy sheet has the same composition as the molten alloy, has a grain size of 10 to 25 μm, is superior in bake hardenability, bendability, and surface quality (orange peel), and can be manufactured with low cost.

1 . An aluminum alloy sheet containing following components: 0.40% to 0.65% of Mg, 0.50% to 0.75% of Si, 0.05% to 0.20% of Cr, and 0.10% to 0.40% of Fe, a remainder being Al, said components being essential elements, the sheet having a grain size of 10 to 25 μm. 
     
     
         2 . The aluminum alloy sheet according to  claim 1 , further containing 0.15% or less of Cu. 
     
     
         3 . The aluminum alloy sheet according to  claim 1  or  2 , further containing 0.10% or less of Ti. 
     
     
         4 . A method for manufacturing an aluminum alloy sheet, comprising the steps of preparing a slab having a thickness of 5 to 15 mm with a continuous casting machine by a continuous casting process using molten alloy containing following components: 0.40% to 0.65% of Mg, 0.50% to 0.75% of Si, 0.05% to 0.20% of Cr, and 0.10% to 0.40% of Fe, a remainder being Al, said components being essential elements; winding the slab into a coil; cold-rolling the slab into a sheet; subjecting the sheet to solution heat treatment in such a manner that the sheet is heated to a temperature of 530° C. to 560° C. at a heating rate of 10° C./sec or more and then maintained at the temperature for five seconds or more; quenching the sheet with water; coiling up the sheet; maintaining the sheet at a temperature of 60° C. to 110° C. for a time of three to 12 hours; and then cooling the sheet to room temperature. 
     
     
         5 . A method for manufacturing an aluminum alloy sheet, comprising the steps of preparing a slab having a thickness of 5 to 15 mm with a continuous casting machine by a continuous casting process using molten alloy containing following components: 0.40% to 0.65% of Mg, 0.50% to 0.75% of Si, 0.05% to 0.20% of Cr, and 0.10% to 0.40% of Fe, a remainder being Al, said components being essential elements; winding the slab into a coil; cold-rolling the slab into a sheet; subjecting the sheet to solution heat treatment in such a manner that the sheet is heated to a temperature of 530° C. to 560° C. at a heating rate of. 10° C./sec or more and then maintained at the temperature for five seconds or more; cooling the sheet to a temperature of 70° C. to 115° C.; coiling up the sheet; and then cooling the sheet to room temperature at a cooling rate of 10° C./hour or less. 
     
     
         6 . A method for manufacturing an aluminum alloy sheet, comprising the steps of preparing a slab having a thickness of 10 to 30 mm with a continuous casting machine by a continuous casting process using molten alloy containing following components: 0.40% to 0.65% of Mg, 0.50% to 0.75% of Si, 0.05% to 0.20% of Cr, and 0.10% to 0.40% of Fe, a remainder being Al, said components being essential elements; hot-rolling the slab into a hot-rolled sheet having a thickness of 2 to 8 mm; winding the hot-rolled sheet into a coil; cold-rolling the hot-rolled sheet into a cold-rolled sheet; subjecting the cold-rolled sheet to solution heat treatment in such a manner that the sheet is heated to a temperature of 530° C. to 560° C. at a heating rate of 10° C./sec or more and then maintained at the temperature for five seconds or more; quenching the sheet with water; coiling up the sheet; maintaining the sheet at a temperature of 60° C. to 110° C. for a time of three to 12 hours; and then cooling the sheet to room temperature. 
     
     
         7 . A method for manufacturing an aluminum alloy sheet, comprising the steps of preparing a slab having a thickness of 10 to 30 mm with a continuous casting machine by a continuous casting process using molten alloy containing following components: 0.40% to 0.65% of Mg, 0.50% to 0.75% of Si, 0.05% to 0.20% of Cr, and 0.10% to 0.40% of Fe, a remainder being Al, said components being essential elements; hot-rolling the slab into a hot-rolled sheet having a thickness of 2 to 8 mm; winding the hot-rolled sheet into a coil; cold-rolling the hot-rolled sheet into a cold-rolled sheet; subjecting the cold-rolled sheet to solution heat treatment in such a manner that the sheet is heated to a temperature of 530° C. to 560° C. at a heating rate of 10° C./sec or more and then maintained at the temperature for five seconds or more; cooling the resulting sheet to a temperature of 70° C. to 115° C.; coiling up the sheet; and then cooling the sheet to room temperature at a cooling rate of 10° C./hour or less. 
     
     
         8 . The method for manufacturing an aluminum alloy sheet according to any one of  claims 4  to  7 , wherein the molten alloy further contains 0.15% or less of Cu and/or 0.10% or less of Ti. 
     
     
         9 . (canceled) 
     
     
         10 . The method for manufacturing an aluminum alloy sheet according to any one of  claims 4  to  7 , wherein the cold-rolling step is performed with a reduction ratio of 20% or more per pass. 
     
     
         11 . The method for manufacturing an aluminum alloy sheet according to  claim 8 , wherein the cold-rolling step is performed with a reduction ratio of 20% or more per pass.