Aluminum alloy sheet with excellent formability and paint bake hardenability and method for production thereof

Abstract

A sheet of a 6000 type aluminum alloy containing Si and Mg as main alloy components and having an excellent formability sufficient to allow flat hemming, excellent resistance to denting, and good hardenability during baking a coating, which exhibits an anisotropy of Lankford values of more than 0.4 or the strength ratio for cube orientations of the texture thereof of 20 or more, and exhibits a minimum bend radius of 0.5 mm or less at 180° bending, even when the offset yield strength thereof exceeds 140 MPa through natural aging; and a method for producing the sheet of the aluminum alloy, which includes the steps of subjecting an ingot to a homogenization treatment, cooling to a temperature lower than 350° C. at a cooling rate of 100° C./hr or more, optionally to room temperature, heating again to a temperature of 300 to 500° C. and subjecting it to hot rolling, cold rolling the hot rolled product, and subjecting the cold rolled sheet to a solution treatment at a temperature of 400° C. or higher, followed by quenching.

1 . A method for producing an aluminum alloy sheet with excellent bendability and paint bake hardenability, said aluminum alloy sheet having an intensity ratio of cube orientation of crystal graphic texture of 20 or more and being made from an aluminum alloy comprising 0.5-2.0 mass % of Si, 0.2-1.5 mass % of Mg, with the relationship 0.7 Si mass %+Mg mass %≦2.2% being satisfied, and the balance consisting of Al and impurities, the method comprising homogenizing an ingot of the aluminum alloy at a temperature of 450° C. or more, cooling the ingot to a specific temperature of less than 350° C. at a cooling rate of 100° C./h or more, hot-rolling the ingot at the specific temperature to form a hot-rolled product, cold-rolling the hot-rolled product to form a cold-rolled product, subjecting the cold-rolled product to a solution heat treatment at a temperature of 450° C. or more, and quenching. 
     
     
         2 . A method for producing an aluminum alloy sheet with excellent bendability and paint bake hardenability, said aluminum alloy sheet having an intensity ratio of cube orientation of crystal graphic texture of 20 or more and being made from an aluminum alloy comprising 0.5-2.0 mass % of Si, 0.2-1.5 mass % of Mg, with the relationship 0.7 Si mass %+Mg mass %≦2.2% being satisfied, and the balance consisting of Al and impurities, the method comprising homogenizing an ingot of the aluminum alloy at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 350° C. at a cooling rate of 100° C./h or more, heating the ingot to a temperature of 300-500° C. and starting hot-rolling of the ingot to form a hot-rolled product, cold-rolling the hot-rolled product to form a cold-rolled product, subjecting the cold-rolled product to a solution heat treatment at a temperature of 450° C. or more, and quenching. 
     
     
         3 . A method for producing an aluminum alloy sheet with excellent bendability and paint bake hardenability, said aluminum alloy sheet having an intensity ratio of cube orientation of crystal graphic texture of 20 or more and being made from an aluminum alloy comprising 0.5-2.0 mass % of Si, 0.2-1.5 mass % of Mg, with the relationship 0.7 Si mass %+Mg mass %≦2.2% being satisfied, and the balance consisting of Al and impurities, the method comprising homogenizing an ingot of the aluminum alloy at a temperature of 450° C. or more, cooling the ingot to a temperature of less than 350° C. at a cooling rate of 100° C./h or more, cooling the ingot to room temperature, heating the ingot to a temperature of 300-500° C. and starting hot-rolling of the ingot to form a hot-rolled product, cold-rolling the hot-rolled product to form a cold-rolled product, subjecting the cold-rolled product to a solution heat treatment at a temperature of 450° C. or more, and quenching. 
     
     
         4 . The method for producing the aluminum alloy sheet according to  claim 1 , wherein the hot-rolling is finished at a temperature of 300° C. or less. 
     
     
         5 . The method for producing the aluminum alloy sheet according to  claim 1 , comprising quenching the solution-treated product to 120° C. at a cooling rate of 5° C./s or more, and subjecting the quenched product to a heat treatment at a temperature of 40-120° C. for 50 hours or less within 60 minutes after the quenching. 
     
     
         6 . The method for producing the aluminum alloy sheet according to  claim 5 , comprising subjecting the heat-treated product to a reversion treatment at a temperature of 170-230° C. for 60 seconds or less within seven days after the heat treatment. 
     
     
         7 . The method for producing the aluminum alloy sheet according to  claim 2 , wherein the hot rolling is finished at a temperature of 300° C. or less. 
     
     
         8 . The method for producing the aluminum alloy sheet according to  claim 2 , comprising quenching the solution-treated product to 120° C. at a cooling rate of 5° C./s or more, and subjecting the quenched product to a heat treatment at a temperature of 40-120° C. for 50 hours or less within 60 minutes after the quenching. 
     
     
         9 . The method for producing the aluminum alloy sheet according to  claim 8 , comprising subjecting the heat-treated product to a reversion treatment at a temperature of 170-230° C. for 60 seconds or less within seven days after the heat treatment. 
     
     
         10 . The method for producing the aluminum alloy sheet according to  claim 3 , wherein the hot rolling is finished at a temperature of 300° C. or less. 
     
     
         11 . The method for producing the aluminum alloy sheet according to  claim 3 , comprising quenching the solution-treated product to 120° C. at a cooling rate of 5° C./s or more, and subjecting the quenched product to a heat treatment at a temperature of 40-120° C. for 50 hours or less within 60 minutes after the quenching. 
     
     
         12 . The method for producing the aluminum alloy sheet according to  claim 11 , comprising subjecting the heat-treated product to a reversion treatment at a temperature of 170-230° C. for 60 seconds or less within seven days after the heat treatment. 
     
     
         13 . The method for producing the aluminum alloy sheet according to  claim 1 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         14 . The method for producing the aluminum alloy sheet according to  claim 4 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         15 . The method for producing the aluminum alloy sheet according to  claim 5 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         16 . The method for producing the aluminum alloy sheet according to  claim 6 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         17 . The method for producing the aluminum alloy sheet according to  claim 2 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         18 . The method for producing the aluminum alloy sheet according to  claim 7 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         19 . The method for producing the aluminum alloy sheet according to  claim 8 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         20 . The method for producing the aluminum alloy sheet according to  claim 9 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         21 . The method for producing the aluminum alloy sheet according to  claim 3 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         22 . The method for producing the aluminum alloy sheet according to  claim 10 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         23 . The method for producing the aluminum alloy sheet according to  claim 11 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B. 
     
     
         24 . The method for producing the aluminum alloy sheet according to  claim 12 , wherein the aluminum alloy further comprises at least one of up to 0.5 mass % of Zn, up to 1.0 mass % of Cu, up to 1.0 mass % of Mn, up to 0.3 mass % of Cr, up to 0.2 mass % of V, up to 0.2 mass % of Zr, up to 0.1 mass % of Ti and up to 50 ppm of B.