Continuous casting process for producing aluminum alloys having low earing

Abstract

The present invention provides an improved process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the steps of continuously annealing the cold rolled strip in an intermediate anneal using an induction heater and/or continuously annealing the hot rolled strip in an induction heater. The alloy composition has mechanical properties that can be varied selectively by varying the time and temperature of a stabilizing anneal.

What is claimed is:  
     
         1 . A method for fabricating aluminum alloy sheet, comprising: 
 (a) continuously casting an aluminum alloy melt to form a cast strip;    (b) continuously imparting electromagnetic energy to the cast strip to form a heated cast strip having a temperature greater than a recrystallization temperature of the cast strip; and    (c) further processing the heated cast strip to form aluminum alloy sheet.    
     
     
         2 . The method of  claim 1 , wherein the continuously casting step is performed by a continuous caster.  
     
     
         3 . The method of  claim 1 , wherein the continuously imparting step is performed by continuously passing the cast strip through a solenoidal heater.  
     
     
         4 . The method of  claim 1 , wherein the cast strip has a cast output temperature ranging from about 426 to about 538° C. and the output temperature of the heated cast strip ranges from about 432 to about 565° C.  
     
     
         5 . The method of  claim 1 , wherein the cast strip has a gauge of no more than about 24 mm.  
     
     
         6 . The method of  claim 1 , wherein the continuously imparting step is performed before hot rolling of the cast strip.  
     
     
         7 . The method of  claim 1 , wherein the continuously imparting step is performed between hot rolling stands.  
     
     
         8 . The method of  claim 1 , wherein step (c) comprises the step of: 
 hot rolling one of the cast strip and heated cast strip to form a hot rolled strip, wherein the hot rolled strip is free of annealing directly after the hot rolling step.    
     
     
         9 . The method of  claim 1 , wherein step (c) comprises the step of: 
 recrystallizing the heated cast strip.    
     
     
         10 . The method of  claim 9 , wherein the recrystallization step is performed in the absence of heating after the continuously imparting step.  
     
     
         11 . The method of  claim 1 , wherein step (c) comprises the step of: 
 hot rolling the heated cast strip to form a hot rolled strip, wherein the hot rolling step reduces the gauge of the cast strip by about 88 to about 94 percent.    
     
     
         12 . The method of  claim 11 , wherein the hot rolled strip has a gauge ranging from about 1.45 to about 3.17 mm.  
     
     
         13 . The method of  claim 1 , wherein the cast strip has a gauge ranging from about 12 to about 19 mm.  
     
     
         14 . The method of  claim 1 , wherein the aluminum alloy melt comprises: 
 (a) from about 3.5 to about 4.9% by weight magnesium;    (b) from about 0.05 to about 0.5% by weight manganese;    (c) from about 0.05 to about 0.15% by weight copper;    (d) from about 0.05 to about 0.35% by weight iron; and    (e) from about 0.05 to about 0.20% by weight silicon, the balance being aluminum and incidental additional materials and impurities.    
     
     
         15 . The method of  claim 14 , wherein step (c) comprises: 
 hot rolling the heated cast strip to form a hot rolled strip;    cold rolling the hot rolled strip to form a cold rolled sheet having a gauge of no more than about 0.021 inches; and    annealing the cold rolled sheet at an annealing temperature to form the aluminum alloy sheet.    
     
     
         16 . The method of  claim 15 , wherein, in the cold rolling step, the gauge of the hot rolled strip is reduced by at least about 70% to form the aluminum alloy sheet.  
     
     
         17 . The method of  claim 15 , wherein the annealing temperature ranges from about 149 to about 200° C.  
     
     
         18 . The method of  claim 15 , wherein the annealing step comprises magnetically inducing a magnetic flux in the cold rolled sheet.  
     
     
         19 . The method of  claim 15 , wherein the aluminum alloy sheet has an as-rolled yield strength of at least about 41 ksi.  
     
     
         20 . The method of  claim 15 , wherein the aluminum alloy sheet has an as-rolled tensile strength of at least about 49 ksi.  
     
     
         21 . The method of  claim 11 , wherein the aluminum alloy sheet has an elongation at break of at least about 3 percent.  
     
     
         22 . The method of  claim 1 , wherein the cast strip is outputted from a continuous caster at a cast output temperature and further comprising between steps (a) and (b): 
 maintaining the cast strip at or near a cast output temperature.    
     
     
         23 . The method of  claim 1 , wherein the aluminum alloy melt comprises: 
 (a) from about 0.9 to about 1.5% by weight magnesium;    (b) from about 0.85 to about 1.2% by weight manganese;    (c) from about 0.05 to about 0.5% by weight copper;    (d) from about 0.05 to about 0.6% by weight iron; and    (e) from about 0.05 to about 0.5% by weight silicon, the balance being aluminum and incidental additional materials and impurities.    
     
     
         24 . The method of  claim 23 , wherein step (c) comprises: 
 hot rolling the heated cast strip to form a hot rolled strip;    cold rolling the hot rolled strip to form a partially cold rolled sheet, wherein in the cold rolling step the gauge of the hot rolled strip is reduced by at least about 50%;    annealing the partially cold rolled strip at an intermediate annealing temperature to form an intermediate annealed cold rolled sheet; and    further cold rolling the intermediate annealed cold rolled sheet to form the aluminum alloy sheet, wherein the gauge of the intermediate annealed cold rolled sheet is reduced by less than about 55%.    
     
     
         25 . The method of  claim 24 , further comprising: 
 further annealing the aluminum alloy sheet to form a further annealed aluminum alloy sheet, wherein in the further annealing step at least one of the yield and ultimate tensile strengths of the aluminum alloy sheet is increased.    
     
     
         26 . The method of  claim 1 , wherein the aluminum alloy melt comprises: 
 (a) from about 3.8 to about 5.2% by weight magnesium;    (b) from about 0.05 to about 0.2% by weight manganese;    (c) from about 0.05 to about 0.15% by weight copper;    (d) from about 0.2 to about 0.35% by weight iron; and    (e) from about 0.05 to about 0.2% by weight silicon, the balance being aluminum and incidental sadditional materials and impurities.    
     
     
         27 . A method for fabricating aluminum alloy sheet, comprising: 
 (a) continuously casting an aluminum alloy melt to form a cast strip, wherein the cast strip, when outputted from the continuous caster, has a cast output temperature;    (b) continuously imparting electromagnetic energy to the cast strip to form a heated cast strip having a temperature greater than the cast output temperature; and    (c) further processing the heated cast strip to form aluminum alloy sheet.    
     
     
         28 . The method of  claim 27 , wherein, in the continuously imparting step, the temperature of the heated cast strip is greater than a recrystallization temperature of the cast strip.  
     
     
         29 . The method of  claim 27 , wherein the continuously imparting step is performed by continuously passing the cast strip through a solenoidal heater.  
     
     
         30 . The method of  claim 27 , wherein the output temperature of the cast strip ranges from about 426 to about 538° C. and the output temperature of the heated cast strip ranges from about 432 to about 565° C.  
     
     
         31 . The method of  claim 27 , wherein the cast strip has a gauge ranging from about 14 mm to about 19 mm.  
     
     
         32 . The method of  claim 27 , wherein the continuously imparting step is performed before hot rolling of the cast strip.  
     
     
         33 . The method of  claim 27 , wherein the continuously imparting step is performed between hot rolling stands.  
     
     
         34 . The method of  claim 27 , wherein step (c) comprises the step of: 
 hot rolling one of the cast strip and heated cast strip to form a hot rolled strip, wherein the hot rolled strip is free of annealing directly after the hot rolling step.    
     
     
         35 . The method of  claim 28 , wherein step (c) comprises the step of: 
 recrystallizing the heated cast strip.    
     
     
         36 . The method of  claim 35 , wherein the recrystallization step is performed in the absence of heating after the continuously imparting step.  
     
     
         37 . The method of  claim 27 , wherein step (c) comprises the step of: 
 hot rolling the heated cast strip to form a hot rolled strip, wherein the hot rolling step reduces the gauge of the cast strip by about 88 to about 94 percent.    
     
     
         38 . The method of  claim 37 , wherein the hot rolled strip has a gauge ranging from about 1.45 to about 3.17 mm.  
     
     
         39 . The method of  claim 27 , wherein the cast strip has a gauge ranging from about 12 to about 19 mm.  
     
     
         40 . The method of  claim 27 , wherein the aluminum alloy melt comprises: 
 (a) from about 3.5 to about 4.9% by weight magnesium;    (b) from about 0.05 to about 0.5% by weight manganese;    (c) from about 0.05 to about 0.15% by weight copper;    (d) from about 0.05 to about 0.35% by weight iron; and    (e) from about 0.05 to about 0.20% by weight silicon, the balance being aluminum and incidental additional materials and impurities.    
     
     
         41 . The method of  claim 40 , wherein step (c) comprises: 
 hot rolling the heated cast strip to form a hot rolled strip;    cold rolling the hot rolled strip to form a cold rolled sheet having a gauge of no more than about 0.021 inches; and    annealing the cold rolled sheet at an annealing temperature to form the aluminum alloy sheet.    
     
     
         42 . The method of  claim 41 , wherein, in the cold rolling step, the gauge of the hot rolled strip is reduced by at least about 70% to form the aluminum alloy sheet.  
     
     
         43 . The method of  claim 41 , wherein the annealing temperature ranges from about 149 to about 200° C.  
     
     
         44 . The method of  claim 41 , wherein the annealing step comprises magnetically inducing a magnetic flux in the cold rolled sheet using a transflux induction heater.  
     
     
         45 . The method of  claim 41 , wherein the aluminum alloy sheet has an as-rolled yield strength of at least about 41 ksi.  
     
     
         46 . The method of  claim 41 , wherein the aluminum alloy sheet has an as-rolled tensile strength of at least about 49 ksi.  
     
     
         47 . The method of  claim 40 , wherein the aluminum alloy sheet has an elongation at break of at least about 3 percent.  
     
     
         48 . The method of  claim 27 , wherein the cast strip is outputted from a continuous caster at a cast output temperature and further comprising between steps (a) and (b): 
 (d) maintaining the cast strip at or near a cast output temperature.    
     
     
         49 . The method of  claim 27 , wherein the aluminum alloy melt comprises: 
 (a) from about 0.9 to about 1.5% by weight magnesium;    (b) from about 0.85 to about 1.2% by weight manganese;    (c) from about 0.05 to about 0.5% by weight copper;    (d) from about 0.05 to about 0.6% by weight iron; and    (e) from about 0.05 to about 0.5% by weight silicon, the balance being aluminum and incidental additional materials and impurities.    
     
     
         50 . The method of  claim 49 , wherein step (c) comprises: 
 hot rolling the heated cast strip to form a hot rolled strip;    cold rolling the hot rolled strip to form a partially cold rolled sheet, wherein in the cold rolling step the gauge of the hot rolled strip is reduced by at least about 50%;    annealing the partially cold rolled strip at an intermediate annealing temperature to form an intermediate annealed cold rolled sheet; and    further cold rolling the intermediate annealed cold rolled sheet to form the aluminum alloy sheet, wherein the gauge of the intermediate annealed cold rolled sheet is reduced by less than about 55%.    
     
     
         51 . The method of  claim 50 , further comprising: 
 further annealing the aluminum alloy sheet to form a further annealed aluminum alloy sheet, wherein in the further annealing step at least one of the yield and ultimate tensile strengths of the aluminum alloy sheet is increased.    
     
     
         52 . The method of  claim 27 , wherein the aluminum alloy melt comprises: 
 (a) from about 3.8 to about 5.2% by weight magnesium;    (b) from about 0.05 to about 0.2% by weight manganese;    (c) from about 0.05 to about 0.15% by weight copper;    (d) from about 0.2 to about 0.35% by weight iron; and    (e) from about 0.05 to about 0.2% by weight silicon, the balance being aluminum and incidental additional materials and impurities.