Methods of reducing surface roughness and improving oxide coating thickness uniformity for anodized aluminum-silicon alloys

Abstract

In one exemplary method, an anodized aluminum-silicon alloy work piece may be formed from an aluminum-silicon alloy substrate material by applying a friction stir processing treatment to the aluminum-silicon alloy substrate material to reduce an average particle size of a plurality of silicon particles contained within the substrate material while increasing a size uniformity of the plurality of silicon particles, and subsequently anodizing said aluminum-silicon alloy substrate material.

1 . A method for forming an anodized aluminum-silicon alloy work piece comprising:
 providing a cast aluminum-silicon alloy substrate material having a plurality of silicon particles;   applying a friction stir processing treatment to said cast aluminum-silicon alloy substrate material to reduce an average particle size of said plurality of silicon particles while increasing a size uniformity of said plurality of silicon particles; and   subsequently anodizing said cast aluminum-silicon alloy substrate material to form an oxide coating layer on said aluminum-silicon alloy substrate material.   
     
     
         2 . The method of  claim 1 , wherein said cast aluminum-silicon alloy substrate material comprises a cast hypoeutectic aluminum-silicon alloy substrate material. 
     
     
         3 . The method of  claim 1 , wherein said cast aluminum-silicon alloy substrate material comprises a cast eutectic aluminum-silicon alloy substrate material. 
     
     
         4 . The method of  claim 1 , wherein said cast aluminum-silicon alloy substrate material comprises a cast hypereutectic aluminum-silicon alloy substrate material. 
     
     
         5 . The method of  claim 1 , wherein applying a friction stir processing treatment to said cast aluminum-silicon alloy substrate material comprises:
 providing a friction stir tool having a profiled pin;   rotating said friction stir tool at a desired rotational speed; and   plunging said rotating profiled pin into an outer surface of said cast aluminum-silicon alloy substrate material to alter a microstructure of said substrate material to reduce an average particle size of said plurality of silicon particles and to provide a narrower size distribution of said plurality of silicon particles.   
     
     
         6 . The method of  claim 5  further comprising:
 traversing said cast aluminum-silicon alloy substrate material in a first direction at a first travel speed such that said rotating profiled pin friction stirs an additional portion of said outer surface. 
 
     
     
         7 . The method of  claim 5  further comprising:
 rotating said cast aluminum-silicon alloy substrate material at a first rotational speed such that said rotating profiled pin friction stirs an additional portion of said outer surface, wherein said cast aluminum-silicon alloy substrate material comprises a cylindrical cast aluminum-silicon alloy substrate material. 
 
     
     
         8 . The method of  claim 1 , wherein subsequently anodizing said aluminum-silicon alloy substrate material to form an oxide coating layer on said cast aluminum-silicon alloy substrate material comprises anodizing said aluminum-silicon alloy substrate material using a Type III anodizing process to form an oxide coating layer. 
     
     
         9 . The method of  claim 8 , wherein said average particle size of said plurality of silicon particles is about 2 micrometers. 
     
     
         10 . The method of  claim 1 , wherein subsequently anodizing said cast aluminum-silicon alloy substrate material to form an oxide coating layer on said aluminum-silicon alloy substrate material comprises anodizing said aluminum-silicon alloy substrate material using a Type II anodizing process to form an oxide coating layer. 
     
     
         11 . A method for forming an anodized aluminum-silicon alloy piston comprising:
 casting a piston having at least one ring groove area from an aluminum-silicon alloy material, said aluminum-silicon alloy material including a plurality of silicon particles;   applying a friction stir processing treatment to said ring groove area to reduce an average particle size of said plurality silicon particles and to increase the size uniformity of said plurality of silicon particles;   machining ring grooves in the ring groove area; and   anodizing said ring groove area to form an oxide coating layer.   
     
     
         12 . The method of  claim 11 , wherein applying a friction stir processing treatment to said ring groove area comprises:
 providing a friction stir tool having a profiled pin;   rotating said friction stir tool at a desired rotational speed;   coupling said piston to a rotating device;   rotating said piston at a desired rotational rate; and   plunging said rotating profiled pin into an outer surface layer of said ring groove area to alter a microstructure of said ring groove area to reduce an average particle size of said plurality of silicon particles and to provide a narrower size distribution of said plurality of silicon particles.   
     
     
         13 . The method of  claim 11 , wherein anodizing said ring groove comprises anodizing said ring groove using a Type II anodization process. 
     
     
         14 . The method of  claim 13 , wherein anodizing said ring groove using a Type II anodization process comprises:
 introducing said piston to a room temperature sulfuric acid bath; and   applying a voltage to said room temperature sulfuric acid bath for a period of time sufficient to form a barrier oxide layer of a desired thickness on said ring groove.   
     
     
         15 . The method of  claim 14 , wherein said desired thickness is about 15 micrometers. 
     
     
         16 . The method of  claim 11 , wherein anodizing said ring groove comprises anodizing said ring groove using a Type II anodization process. 
     
     
         17 . A method for reducing barrier oxide coating layer surface roughness and increasing barrier oxide coating layer thickness uniformity in an anodized aluminum-silicon alloy work piece, the method comprising:
 providing a cast aluminum-silicon alloy substrate material having a cast microstructure, said cast microstructure including a plurality of silicon particles; and   applying a friction stir process to a surface of a cast aluminum-silicon alloy substrate material prior to anodization to transform said cast microstructure to a wrought microstructure, wherein said transformation also reduces an average particle size of said plurality of silicon particles within said wrought microstructure and narrows a size distribution of said plurality of silicon particles.   
     
     
         18 . The method of  claim 17 , wherein applying a friction stir processing treatment comprises:
 providing a friction stir tool having a profiled pin;   rotating said friction stir tool at a desired rotational speed; and   plunging said rotating profiled pin into an outer surface layer of said cast aluminum-silicon alloy substrate material at sufficient force to alter said cast microstructure to a wrought microstructure.