Method for improving formability of hexagonal close packed metals

Abstract

A method of improving the formability of a strip of sheet magnesium or other hexagonal closely packed metal is comprised of repeatedly bending, straightening and reverse bending the strip along its entire continuous length to induce plastic deformation and twinning. Twinning reduces and redistributes the grain size of the sheet material to make the sheet material more formable during subsequent metal forming operations. In practice, a coil of sheet magnesium strip is mounted on a spindle. The end of the strip is unwound from the coil and threaded through a series of offset rollers. The end of the strip is connected to a take-up spindle located down stream of the offset rollers. The strip is unwound from the storage spindle and progressively and continuously bent and reverse bent as it traverses around the offset rollers and is recoiled onto a take-up spindle.

1 . A method of improving the formability of a strip of metal of close packed hexagonal microstructure comprising repeatedly bending and then reverse bending the sheet along its entire continuous length to induce plastic deformation and twinning.  
   
   
       2 . The method of claim in  1  which the repeated bending and reverse bending of the strip is obtained by passing the strip through a series of offset rollers so the strip is repeatedly and continuously bent in one direction and then in the other direction.  
   
   
       3 . The method of  claim 2  in which the strip of metal is magnesium.  
   
   
       4 . The method of  claim 3  in which the metal is magnesium AZ31.  
   
   
       5 . The method of  claim 1  Including the further step of, subsequent to the bending and reverse bending, heating the strip of material in the range between 50 degrees Centigrade and 450 degrees Centigrade to re-crystallize the grain structure of the strip.  
   
   
       6 . The method of  claim 2  in which the diameter of the rollers is chosen to provide the desired severity of bending and unbending.  
   
   
       7 . The method of  claim 2  in which the number of rollers is chosen to provide the desired number of times that the strip is bent and reverse bent.  
   
   
       8 . A method of improving the formability of magnesium sheet comprising: passing the sheet through series of offset rollers to effect repeated bending and unbending the sheet along its entire continuous length to induce plastic deformation and twinning whereby the grain size of the sheet is reduced for improved subsequent formability.  
   
   
       9 . The method of  claim 8  in which the number of rollers is selected in accord with the number of bendings and reverse bending to which the sheet will be subjected and the diameter of the rollers is selected in accord with the severity of the bendings and reverse bending to which the sheet will be subjected.  
   
   
       10 . The method of  claim 9  in which the sheet is magnesium AZ321.  
   
   
       11 . The method of  claim 10  including the further step of, subsequent to the bending and reverse bending, heating the strip of material in the range between 50 degrees Centigrade and 450 degrees Centigrade to re-crystallize the grain structure of the strip.  
   
   
       12 . A method of improving the formability of a sheet of magnesium AZ31 comprising: 
 mounting a coil of sheet magnesium on a spindle so that an end of the sheet can be unwound from the coil,    threading the end of the sheet through a series of offset rollers,    and recoiling the end of the sheet on a take-up spindle located downstream from the offset rollers so that sheet of magnesium is repeatedly bent and unbent along its entire continuous length by the offset rollers during uncoiling from the storage spindle and recoiling onto the take-up spindle, whereby to introduce continuous twinning into the sheet of magnesium and thereby modify the grain structure of the sheet material to improve its formability in subsequent forming of the magnesium sheet.    
   
   
       13 . The method of  claim 12  in which the diameter of the rollers is chosen to provide the desired severity of bending and unbending.  
   
   
       14 . The method of  claim 12  in which the number of rollers is chosen to provide the desired number of times that the strip is bent and reverse bent.  
   
   
       15 . The method of  claim 12  in which the metal is magnesium AZ31.  
   
   
       16 . The method of  claim 12  including the further step of, subsequent to the bending and reverse bending, heating the strip of material in the range between 50 degrees Centigrade and 450 degrees Centigrade to re-crystallize the grain structure of the strip.