Method of producing superplastic alloys and superplastic alloys produced by the method

Abstract

A method for producing new superplastic alloys by inducing in an alloy the formation of precipitates having a sufficient size and homogeneous distribution that a sufficiently refined grain structure to produce superplasticity is obtained after subsequent PSN processing. An age-hardenable alloy having at least one dispersoid phase is selected for processing. The alloy is solution heat-treated and cooled to form a supersaturated solid solution. The alloy is plastically deformed sufficiently to form a high-energy defect structure useful for the subsequent heterogeneous nucleation of precipitates. The alloy is then aged, preferably by a multi-stage low and high temperature process, and precipitates are formed at the defect sites. The alloy then is subjected to a PSN process comprising plastically deforming the alloy to provide sufficient strain energy in the alloy to ensure recrystallization, and statically recrystallizing the alloy. A grain structure exhibiting new, fine, equiaxed and uniform grains is produced in the alloy. An exemplary 6xxx alloy of the type capable of being produced by the present invention, and which is useful for aerospace, automotive and other applications, is disclosed and claimed. The process is also suitable for processing any age-hardenable aluminum or other alloy.

What is claimed is:  
     
         1 . A method for producing a superplastic alloy, said method comprising: 
 providing an alloy for processing, said alloy comprising a matrix phase and at least two alloying elements, at least one of said alloying elements being, or being capable of forming, a dispersoid phase substantially insoluble in said matrix phase;    solution heat treating said alloy;    cooling the alloy to form a supersaturated solid solution;    plastically deforming said alloy in a first deformation step sufficiently to form a high-energy defect structure, thereby forming nucleation sites useful for the subsequent nucleation of precipitates;    aging said alloy, thereby forming precipitates at said nucleation sites; and    plastically deforming said alloy in a second deformation step, and statically recrystallizing said alloy, through a particle-stimulated nucleation process.    
     
     
         2 . The method of    claim 1   , wherein said step of providing an alloy for processing comprises providing an aluminum alloy.  
     
     
         3 . The method of    claim 2   , wherein said aluminum alloy is selected from the group consisting of aluminum alloys 6013, 6111, 6061, 6063, and 6066.  
     
     
         4 . The method of    claim 1   , wherein said cooling step comprises quenching.  
     
     
         5 . The method of    claim 1   , wherein said first deformation step comprises plastically deforming said alloy sufficiently to form deformation bands.  
     
     
         6 . The method of    claim 1   , wherein said first deformation step comprises cold rolling said alloy.  
     
     
         7 . The method of    claim 6   , wherein said first deformation step further comprises cold rolling said alloy at room temperature.  
     
     
         8 . The method of    claim 7   , wherein said first deformation step further comprises cold rolling said alloy to a reduction of at least about 30%.  
     
     
         9 . The method of    claim 1   , wherein said aging step comprises a first heating step at a first temperature and a second heating step at a second higher temperature.  
     
     
         10 . The method of    claim 9   , wherein said precipitates are formed during said first heating step and coarsened during said second heating step.  
     
     
         11 . The method of    claim 9   , wherein said alloy is cooled after said first heating step and after said second heating step.  
     
     
         12 . The method of    claim 1   , wherein said second deformation step comprises cold rolling said alloy.  
     
     
         13 . The method of    claim 12   , wherein said second deformation step further comprises cold rolling said alloy at room temperature.  
     
     
         14 . The method of    claim 1   , wherein said static recrystallization step comprises rapidly heating said alloy to a temperature at which recrystallization occurs.  
     
     
         15 . The method of    claim 1   , wherein said static recrystallization step comprises heating said alloy to a temperature in the range of a solution heat-treatment temperature for said alloy.  
     
     
         16 . The method of    claim 1   , wherein said static recrystallization step comprises heating said alloy to a superplastic forming temperature of said alloy.  
     
     
         17 . A method for producing a superplastic aluminum alloy, said method comprising: 
 providing an alloy for processing, said alloy being a 6013/6111 alloy;    solution heat treating said alloy;    cooling the alloy to form a supersaturated solid solution;    plastically deforming said alloy in a first deformation step sufficiently to form a high-energy defect structure, thereby forming nucleation sites useful for the subsequent nucleation of precipitates;    aging said alloy, thereby forming precipitates at said nucleation sites;    plastically deforming said alloy in a second deformation step to provide sufficient strain energy in said alloy to ensure recrystallization; and    statically recrystallizing said alloy.    
     
     
         18 . The method of    claim 17   , wherein said 6013/6111 alloy has the approximate composition 97.3 wt % Al-0.8 wt % Mg-0.7 wt % Si-0.8 wt % Cu-0.3 wt % Mn-0.1 wt % Fe.  
     
     
         19 . The method of    claim 17   , wherein said solution heat treating step is performed at a temperature of about 540° C. for about one hour.  
     
     
         20 . The method of    claim 17   , wherein said cooling step comprises quenching.  
     
     
         21 . The method of    claim 17   , wherein said first deformation step comprises cold rolling said alloy.  
     
     
         22 . The method of    claim 21   , wherein said first deformation step comprises cold rolling said alloy to a reduction of at least about 30%.  
     
     
         23 . The method of    claim 22   , wherein said first deformation step comprises cold rolling said alloy to a reduction of at least about 60%.  
     
     
         24 . The method of    claim 17   , wherein said first deformation step comprises plastically deforming said alloy sufficiently to form deformation bands.  
     
     
         25 . The method of    claim 17   , wherein said first deformation step is performed such that, after subsequent aging, said alloy exhibits globular or near-spheroid shaped precipitates.  
     
     
         26 . The method of    claim 17   , wherein said aging step comprises a first heating step at a first temperature and a second heating step at a second higher temperature.  
     
     
         27 . The method of    claim 26   , wherein said precipitates are formed during said first heating step and coarsened during said second heating step.  
     
     
         28 . The method of    claim 26   , wherein said alloy is cooled after said first heating step and after said second heating step.  
     
     
         29 . The method of    claim 26   , wherein said first heating step is performed at about 300° C. and said second heating step is performed at about 380° C.  
     
     
         30 . The method of    claim 29   , wherein the duration of said first heating step is about 24 hours, and the duration of said second heating step is about 24 hours.  
     
     
         31 . The method of    claim 26   , wherein said first heating step is performed at about 300° C. and said second heating step is performed at about 450° C.  
     
     
         32 . The method of    claim 31   , wherein the duration of said first heating step is about 24 hours, and the duration of said second heating step is about 2 hours.  
     
     
         33 . The method of    claim 17   , wherein said aging step comprises heating said alloy at a temperature of about 450° C. for about 2 hours.  
     
     
         34 . The method of    claim 17   , wherein said second deformation step comprises cold rolling said alloy.  
     
     
         35 . The method of    claim 34   , wherein said second deformation step comprises cold rolling said alloy to a reduction of at least about 80%.  
     
     
         36 . The method of    claim 35   , wherein said second deformation step comprises cold rolling said alloy to a reduction of at least about 87%.  
     
     
         37 . The method of    claim 36   , wherein said second deformation step comprises cold rolling said alloy to a reduction of at least about 92%.  
     
     
         38 . The method of    claim 17   , wherein said static recrystallization step comprises rapidly heating said alloy to a temperature at which recrystallization occurs.  
     
     
         39 . The method of    claim 38   , wherein said static recrystallization step comprises heating said alloy to a temperature of about 540° C. for about 5 minutes.  
     
     
         40 . A 6xxx aluminum alloy having a microstructure comprising grains having an average size in the range of about 9.5 μm to about 11.6 μm, said grain sizes having a standard deviation in the range of about 4.7 μm to about 5.6 μm, and said grains further having an average grain aspect ratio in the range of about 1.6 to about 1.9, said grain aspect ratios having a standard deviation in the range of about 0.6 to about 0.8.  
     
     
         41 . The 6xxx aluminum alloy of    claim 40   , wherein said alloy has a grain roundness in the range of about 1.6 to about 1.8.  
     
     
         42 . The 6xxx aluminum alloy of    claim 40   , wherein said alloy comprises grains having an average size of about 9.5 μm, said grain sizes having a standard deviation of about 4.7 μm, and said grains further having an average grain aspect ratio of about 1.6, said grain aspect ratios having a standard deviation of about 0.6.  
     
     
         43 . The 6xxx aluminum alloy of    claim 40   , wherein said alloy exhibits a maximum elongation of at least about 350%.  
     
     
         44 . The 6xxx aluminum alloy of    claim 40   , wherein said alloy exhibits a maximum strain rate sensitivity of at least about 0.5.  
     
     
         45 . The 6xxx aluminum alloy of    claim 44   , wherein said alloy exhibits a maximum elongation of at least about 375%.  
     
     
         46 . A superplastic 6xxx aluminum alloy having a maximum strain rate sensitivity of at least about 0.5 and exhibiting a maximum elongation of at least about 350%, and being produced according to a process comprising: 
 providing an alloy for processing, said alloy comprising a matrix phase and at least two alloying elements, at least one of said alloying elements being, or being capable of forming, a dispersoid phase substantially insoluble in said matrix phase;    solution heat-treating said alloy;    cooling the alloy to form a supersaturated solid solution;    plastically deforming said alloy in a first deformation step sufficiently to form a high-energy defect structure, thereby forming nucleation sites useful for the subsequent nucleation of precipitates;    aging said alloy, thereby forming precipitates at said nucleation sites; and    plastically deforming said alloy in a second deformation step, and statically recrystallizing said alloy, through a particle-stimulated nucleation process.