Abstract:
A method for fusing a durable overlay on an aluminum article includes the steps of: providing an article comprising aluminum; and, applying a hypereutectic cladding layer to a at least one surface of the aluminum article by fusing a consumable welding filler material to the aluminum article using a welding process. An article includes an aluminum alloy casting having a hypereutectic cladding layer fused to at least a portion of a surface thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to another application filed on even date herewith and entitled “CONSUMABLE WELDING FILLER METAL FOR CLADDING ALLOYS”, Docket No. 0798.1, the entire disclosure of which is incorporated herein by reference. 
     
    
       [0002] The United States Government has rights in this invention pursuant to contract no. DE-AC05-000R22725 between the United States Department of Energy and UT-Battelle, LLC. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The present invention relates to surface treatments for aluminum alloys, and more particularly to hypereutectic surface treatments for aluminum alloys that are applied using welding processes.  
         BACKGROUND OF THE INVENTION  
         [0004]    Because of decreased weight and advantageous mechanical properties, aluminum alloys are rapidly displacing iron and steel alloys in many industrial and commercial applications. For example, automotive manufacturers utilize aluminum alloys for components that were formerly manufactured using iron or steel alloys to decrease vehicle weight while maintaining the structural integrity of the vehicle. Generally speaking, the lighter the vehicle, the greater its fuel efficiency.  
           [0005]    Unfortunately, components manufactured from aluminum alloys do not share all of the desirable mechanical properties of comparable components manufactured from iron or steel alloys. The abrasion, wear, and corrosion characteristics of iron or steel alloys are generally considered superior to those exhibited by aluminum alloys. If a cost effective way to improve the abrasion, wear, and corrosion characteristics of aluminum alloys could be developed, more aluminum alloys would be used in automotive and other appropriate applications. The result could yield even greater increases in vehicle fuel efficiency that could benefit society fiscally and environmentally.  
           [0006]    One of the most common ways to improve the abrasion, wear, and corrosion characteristics of aluminum alloys is to increase silicon content. Consistent with phase diagrams known to one of ordinary skill in the art, aluminum-silicon alloys form a eutectic when silicon concentrations are approximately 12.6 wt. % silicon. Hypereutectic aluminum alloys, i.e., aluminum alloys having a silicon concentration in excess of 12.6 wt. % silicon, generally have large silicon particles that are very hard. The large silicon particles generally make hypereutectic aluminum alloys more wear resistant than non-eutectic or eutectic aluminum alloys. A common hypereutectic aluminum alloy is Al-390, or alloy 390, which contains approximately 16 to 18 wt. % silicon. Unfortunately, hypereutectic aluminum alloys are generally more difficult to cast and machine. Additionally, increasing silicon concentrations generally has a detrimental effect on the mechanical properties, e.g., ductility, of aluminum alloys.  
           [0007]    Using surface technology to locally increase the silicon concentration of aluminum alloys is one alternative for improving the abrasion, wear, and corrosion resistance characteristics of a manufactured component while maintaining the desirable mechanical properties of its underlying aluminum alloy substrate. Generally, surface layers having high silicon concentrations are produced by depositing silicon or mixtures containing high silicon concentrations onto aluminum alloys and then melting the silicon mixture into the surface of the aluminum alloys by application of heat. Surface heating of silicon-coated aluminum alloys may be accomplished by laser beam processing or infrared heating. Although these heating techniques are effective, they rely on relatively sophisticated and expensive equipment that is usually difficult to use in normal manufacturing situations.  
         OBJECTS OF THE INVENTION  
         [0008]    Accordingly, it is an object of the present invention to provide a means of producing aluminum alloy components that have abrasion, wear, and corrosion resistance characteristics similar to those exhibited by hypereutectic alloys.  
           [0009]    It is another object of the present invention to provide a process for improving the abrasion, wear, and corrosion characteristics of aluminum alloys that utilizes conventional welding techniques.  
           [0010]    It is another object of the present invention to overcome the difficulties encountered in the art by using a welding process to apply a cladding layer to the surface of an aluminum alloy for the purpose of improving the abrasion, wear, and corrosion characteristics of the aluminum alloy.  
           [0011]    Further objects, benefits, and features of the present invention will become apparent to one of ordinary skill in the art from the drawings and description of the preferred embodiments claimed and disclosed herein.  
         SUMMARY OF THE INVENTION  
         [0012]    In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a method for fusing a durable overlay on an aluminum article which includes the steps of: providing an article comprising aluminum; and, applying a hypereutectic cladding layer to a at least one surface of the aluminum article by fusing a consumable welding filler material to the aluminum article using a welding process.  
           [0013]    In accordance with another aspect of the present invention, an article includes an aluminum alloy casting having a hypereutectic cladding layer fused to at least a portion of a surface thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective cutaway of a consumable welding rod showing the outer layer and the inner core material in accordance with the present invention.  
         [0015]    [0015]FIG. 2 is a photograph of an aluminum alloy 319 casting including machined overlay cladding layers on opposing sides in accordance with the present invention.  
         [0016]    [0016]FIG. 3 is a photomicrograph of an overlay cladding layer from the casting shown in FIG. 2. 
     
    
       [0017]    For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring to FIG. 1, certain embodiments of the invention are described as follows. A weld overlay material (filler metal) in the form of a consumable welding rod (or wire)  10  is shown that is used to apply a hypereutectic cladding layer to a surface of an aluminum alloy component or casting. The welding rod is preferably comprised of a ductile metal sheath  12 , or outer layer, surrounding an alloying element, or inner core material  16 . The outer layer  12  may be fabricated from any commercially available aluminum material, e.g., aluminum alloy 1100, and formed into any geometry to encapsulate the inner core material. Preferably, but not necessarily, the outer layer is conformed to a substantially annular or circular cross-sectional geometry. Although the examples discussed herein teach the use of aluminum and aluminum alloys for the outer layer  12  of the consumable welding rod, one of ordinary skill in the art will recognize that combinations and alloys of nickel, iron, molybdenum, titanium, magnesium, and stainless steel may also be used.  
         [0019]    For alloys comprised of at least 50% aluminum, any of the alloys having properties as listed in Table I may be used for the outer layer  12  of the consumable welding rod. The term “XYZ” indicates a plurality of alloys that are within the well-known family of alloys denoted by the leading number identified in Table I.  
                           TABLE I                                   Alloy   Property                           1XYZ   Controlled unalloyed (pure) compositions           2XYZ   Where Cu is the principle alloying element           3XYZ   Where Mn is the principle alloying element           4XYZ   Where Si is the principle alloying element           5XYZ   Where Mg is the principle alloying element           6XYZ   Where Mg and Si are the principle alloying elements           7XYZ   Where Zn is the principle alloying element           8XYZ   Miscellaneous alloys and alloys containing Sn and Li.                      
 
         [0020]    The inner core material  16  is preferably comprised of silicon in at least one of a solid, liquefied, granular, powder, or gelatinous state. The amount of silicon should be selected to produce a consumable welding rod having greater than 12.6 wt. % silicon in order to produce a hypereutectic during the welding process. Although silicon is taught herein as the preferred alloying element comprising the inner core material  16  of the consumable welding rod, one of ordinary skill in the art will recognize that combinations and alloys of boron, cobalt, chromium, copper, iron, magnesium, molybdenum, nickel, niobium, phosphorus, titanium, vanadium, tungsten, zirconium, carbon, nitrogen, and oxygen may also be used in appropriate ratio to produce a hypereutectic during the welding process. It is preferable to use the smallest particle size that can be used without the occurrence of agglomeration.  
         [0021]    The consumable welding rod  10  may be fabricated by utilizing any of a variety of well-known, conventional methods, some of which will result in features such as a seam  14  where the outer layer  12  is joined. For example, a ductile alloy tube can be used to form an outer layer  12  for containing inner core material  16 . Alloy tubes having various dimensions may be used as long as the ratio of outer layer material  12  to inner core material  16  is appropriate to produce a hypereutectic during the welding process.  
       EXAMPLE I  
       [0022]    A high-purity commercial grade aluminum alloy 1100 tube having an initial size of approximately 19 inches long, 0.25 inches outside diameter, and 0.03 inches wall thickness was closed on one end and then filled with pure silicon powder having an approximate grain size of about 100 mesh. After the tube was substantially filled with silicon, the open end of the tube was closed to seal the opening and entrap the silicon in the tube cavity. Once sealed, the tube containing the silicon powder was cold swaged into a wire having an approximate outside diameter of 0.12 inches.  
         [0023]    Conventional production methods can be used to produce consumable welding rods consistent with the present invention in mass-manufacturing environments. For example, silicon inner core material can be deposited on a planar surface of a thin sheet of aluminum alloy, which is then molded to surround the inner core material. Once the aluminum alloy is formed to surround the inner core material, the preformed wire may then be cold swaged into a wire with a desired outer diameter. The preformed wire may be formed from long pieces of sheet aluminum to allow a substantially continuous feed into the cold swage process. The continuous cold swaged wires may then be cut into consumable welding rods having preselected lengths. The ends of the consumable welding rods may be sealed contemporaneously with the cutting process or in a separate step using conventional sealing techniques known to one of ordinary skill in the art.  
         [0024]    Once a consumable welding rod having the appropriate content is obtained, the surface properties of an aluminum alloy casting may be improved by depositing the consumable welding rod on the surface of the casting using welding processes. Although the instant example describes the use of castings comprised of noneutectic aluminum alloys, one of ordinary skill in the art will appreciate that the process may be applied to castings comprised of eutectic aluminum alloys as well. The consumable welding rod is fused to any surface of the casting using manual or automated welding techniques to produce hypereutectic layers on eutectic and noneutectic casting substrates.  
         [0025]    Examples of welding processes that are suitable for fusing the consumable welding rod to the casting substrate include gas-tungsten-arc (GTA), gas metal-arc (GMA), plasma arc (PA), and laser beam (LB) welding processes. One of ordinary skill in the art will recognize that other conventional, well known aluminum welding processes may be used to fuse the consumable welding rod to the aluminum casting.  
         [0026]    The weld overlay may be deposited in any geometry or pattern, e.g., horizontal lines, vertical lines, circles, nonlinear lines, etc., that will be accepted by the surface of the casting. Regardless of the welding process and deposit pattern used, the weld overlay deposit should be free of cracks and should have minor porosity of the type normally associated with aluminum casting welds. Once the overlay is deposited on the casting, it may be machined to conform to a predetermined shape or design.  
         [0027]    [0027]FIG. 2 shows a machined block of an aluminum 319 casting  26  with a machined hypereutectic overlay  24  on two of opposing sides thereof. The weld-casting interfaces  22  can be clearly seen.  
         [0028]    [0028]FIG. 3 is a photomicrograph of the hypereutectic overlay revealing the relatively large silicon particles in the overlay. The microstructure shown is comparable to that of aluminum alloy 390, suggesting that the abrasion, wear, and corrosion properties of the castings are similar to those of aluminum alloy 390. Testing revealed that the hardness of the overlay layer was 117 dph, which is comparable to the 124 dph hardness value of aluminum alloy 390.  
         [0029]    While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be prepared therein without departing from the scope of the inventions defined by the appended claims.