Beverage can body sheet from continuously cast aluminum alloy

Abstract

A continuous casting method and apparatus are described that generate alpha-phase Al(Fe,Mn)Si intermetallic particles on the surface of an aluminum alloy strip to facilitate the manufacture of beverage cans. The alpha phase particle size is generated so that subsequent rolling will ensure the particles will provide galling-free operation in the ironing stages of the can body making process. The control of alpha-particle size upon the surface layers of the strip ensures galling-free operation.

1 . An aluminum alloy sheet product, suitable for the production of cans, made by continuous casting followed by rolling, annealing and cold rolling to final gauge wherein intermetallic particles of alpha phase Al(Fe, Mn)Si of diameters between 0.2 to 35 μm are present on at least one surface of the cast strip such that during the ironing steps of the can making process the product is substantially free of galling defects. 
     
     
         2 . A method of making the product of  claim 1  by continuous casting on molds with surface textures such as grooves or dimples or protrusions so as to produce intermetallic particles of alpha phase Al(Fe, Mn)Si on at least one surface of the cast strip. 
     
     
         3 . The method of  claim 2  wherein the casting mold surfaces have dimples or protrusions of diameter between 0.3 to 0.7 mm and depth or height between 0.01 to 0.2 mm with an area coverage in the range of 5% to 64%. 
     
     
         4 . The method of  claim 2  where the mold surface grooves or dimples or protrusions are produced by shot peening, laser shot blasting, grit blasting, electro-discharge texturing, laser ablation, photoelectric etching, cutting, knurling, roll forming or embossing. 
     
     
         5 . The method of  claim 2  wherein the casting mold is characterized by longitudinal grooves of widths between 0.04 to 0.50 mm and depths between 0.040 to 0.40 mm and groove area coverage between 2% to 75%. 
     
     
         6 . The rolled sheet product of  claim 1  in which the intermetallic particles of alpha phase Al(Fe,Mn)Si are in the diameter range of 0.2 to 15 μm with a median diameter between 2 and 7 um on at least one surface of the sheet. 
     
     
         7 . The cast strip product of  claim 1  in which the surface protrusions due to mold grooves, or mold dimples/protrusions, is 20 μm or less, or 30 μm or less, respectively. 
     
     
         8 . A method of producing an aluminum alloy strip having intermetallic particles of alpha phase Al(Fe, Mn)Si by rapidly heating the strip surface to a temperature near the solidus temperature so as to coarsen the alpha phase Al(Fe, Mn)Si to a median diameter greater than 2 μm. 
     
     
         9 . The method of  claim 8  where at least one surface develops a matte finish indicating the presence of large alpha phase Al(Fe,Mn)Si particles. 
     
     
         10 . The method of  claim 8  wherein the surface reaches a temperature at which the surface develops a matte finish with a maximum average strip temperature 10° C. or more below the solidus temperature. 
     
     
         11 . The method of  claim 8  wherein the surface develops a matte finish with maximum average strip temperature 20° C. or more below the solidus temperature. 
     
     
         12 . An aluminum alloy strip according to  claim 1  that is rolled to finish gauge for making beverage cans that are substantially free of galling.