Highly formable automotive aluminum sheet with reduced or no surface roping and a method of preparation

Abstract

Disclosed are novel processes to increase productivity on a continuous anneal and solution heat treatment line for heat-treatable automotive aluminum sheet products with high T4 and after-paint bake strengths and reduced roping. As a non-limiting example, the processes described herein can be used in the automotive industry. The disclosed heat treatable alloys and processes also may be applicable to the marine, aerospace, and transportation industries.

What is claimed is: 
     
         1 . A method of producing a 6xxx series aluminum sheet, comprising:
 casting a 6xxx series aluminum alloy to form an ingot;   homogenizing the ingot;   hot rolling the ingot to produce a hot rolled intermediate product;   cold rolling the hot rolled intermediate product;   annealing;   cold rolling; and   subjecting the sheet to a continuous anneal and solution heat treatment process.   
     
     
         2 . A method of producing a 6xxx series aluminum sheet, comprising:
 casting a 6xxx series aluminum alloy to form an ingot;   homogenizing the ingot;   hot rolling the ingot to produce a hot rolled intermediate product, followed by:
 a) after exit temperature coiling, immediately placing into an anneal furnace, or 
 b) after exit temperature coiling, cooling to room temperature and then placing into an anneal furnace; 
   annealing;   cold rolling; and   subjecting the sheet to a continuous anneal and solution heat treatment process.   
     
     
         3 . The method of  claim 1 , wherein the aluminum alloy comprises about 0.20-1.0 wt. % Si, 0.11-0.40 wt. % Fe, 0.0-0.23 wt. % Cu, 0.0-0.22 wt. % Mn, 0.50-0.83 wt. % Mg, 0.0-0.25 wt. % Cr, 0.0-0.006 wt. % Ni, 0.0-0.15 wt. % Zn, 0.0-0.17 wt. % Ti, up to 0.15 wt. % impurities, remainder Al. 
     
     
         4 . The method of  claim 1 , wherein the aluminum alloy comprises about 0.60-0.95 wt. % Si, 0.20-0.35 wt. % Fe, 0.05-0.20 wt. % Cu, 0.05-0.20 wt. % Mn, 0.55-0.75 wt. % Mg, 0.0-0.15 wt. % Cr, 0.0-0.006 wt. % Ni, 0.0-0.15 wt. % Zn, 0.0-0.15 wt. % Ti, up to 0.15 wt. % impurities, remainder Al. 
     
     
         5 . The method of  claim 1 , wherein the homogenizing step is performed at a temperature of between about 500-600° C. for a period of up to 10 hours. 
     
     
         6 . The method of  claim 1 , wherein the hot rolling step is performed at a temperature between about 200° C. to 500° C. 
     
     
         7 . The method of  claim 1 , wherein the hot rolling step includes maintaining a temperature of the hot rolled intermediate product to about 300° C. or less upon exit from a hot rolling mill. 
     
     
         8 . The method of  claim 1 , wherein the annealing step includes heating to a temperature of between about 350° C. to 450° C. 
     
     
         9 . The method of  claim 1 , wherein the step of subjecting the sheet to a continuous anneal and solution heat treatment process comprises heating the sheet to a temperature ranging from 500° C. to 580° C. for a period of time. 
     
     
         10 . The method of  claim 9 , wherein the period of time is 1 minute or less. 
     
     
         11 . The method of  claim 1 , further comprising quenching the sheet. 
     
     
         12 . The method of  claim 11 , further comprising reheating the quenched sheet to form a reheated sheet and coiling the reheated sheet. 
     
     
         13 . An aluminum alloy produced by the method of  claim 1 . 
     
     
         14 . The aluminum alloy of  claim 13 , which possesses higher T4 and after-paint bake strengths, decreased roping, and improved hemmability. 
     
     
         15 . The aluminum alloy of  claim 13 , comprising one or more of the following properties: a T4 yield strength of at least 100 MPa; a T4 tensile strength of at least 200 MPa; a T82 yield strength of at least 160 MPa; a uniform and total elongation of at least 20%; or an after paint bake yield strength of at least 200 MPa. 
     
     
         16 . Use of the method of  claim 1  to increase line speed in a CASH production line by at least 10%. 
     
     
         17 . An aluminum alloy comprising about 0.20-1.0 wt. % Si, 0.11-0.40 wt. % Fe, 0.0-0.23 wt. % Cu, 0.0-0.22 wt. % Mn, 0.50-0.83 wt. % Mg, 0.0-0.25 wt. % Cr, 0.0-0.006 wt. % Ni, 0.0-0.15 wt. % Zn, 0.0-0.17 wt. % Ti, up to 0.15 wt. % impurities, with the remainder as Al, wherein the aluminum alloy comprises a yield strength of at least 160 MPa when the aluminum alloy is in a T82 temper. 
     
     
         18 . The aluminum alloy of  claim 17 , comprising about 0.60-0.95 wt. % Si, 0.20-0.35 wt. % Fe, 0.05-0.20 wt. % Cu, 0.05-0.20 wt. % Mn, 0.55-0.75 wt. % Mg, 0.0-0.15 wt. % Cr, 0.0-0.006 wt. % Ni, 0.0-0.15 wt. % Zn, 0.0-0.15 wt. % Ti, up to 0.15 wt. % impurities, with the remainder as Al. 
     
     
         19 . A motor vehicle body part comprising an aluminum alloy comprising about 0.20-1.0 wt. % Si, 0.11-0.40 wt. % Fe, 0.0-0.23 wt. % Cu, 0.0-0.22 wt. % Mn, 0.50-0.83 wt. % Mg, 0.0-0.25 wt. % Cr, 0.0-0.006 wt. % Ni, 0.0-0.15 wt. % Zn, 0.0-0.17 wt. % Ti, up to 0.15 wt. % impurities, with the remainder as Al, wherein the aluminum alloy comprises a yield strength of at least 160 MPa when the aluminum alloy is in a T82 temper. 
     
     
         20 . The motor vehicle body part of  claim 19 , wherein the motor vehicle body part comprises an outer panel.