Abstract:
This invention is directed toward a method for enhancing the wear resistance of an aluminum cylinder bore comprising laser alloying of the cylinder bore with selected precursors. The present invention is particularly well suited for enhancing the wear resistance caused by corrosion in an aluminum block engine comprising aluminum cylinder bores.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is directed toward a method for enhancing the wear resistance of an aluminum cylinder bore comprising laser alloying of the cylinder bore with selected precursors. The present invention is particularly well suited for enhancing the wear resistance in an aluminum block engine comprising aluminum cylinder bores. 
     2. Description of the Prior Art 
     Internal combustion engines comprise cylinder bores which receive reciprocating pistons. These cylinder bores are exposed to harsh environmental conditions, including friction and high temperatures. The harsh environmental conditions result in wear and/or corrosion, thereby reducing the effective life of the aluminum block engine. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a process or method for producing alloyed aluminum cylinder bores for use in an internal combustion engine. The present invention comprises applying a precursor layer comprising a binder and metallic or ceramic powder to the surface of an aluminum cylinder bore, as shown in Block  10  of FIG.  1 . The precursor layer has a thickness in the range of 50-150 microns. 
     The invention further comprises irradiating the cylinder bore with a laser beam at a sufficient energy level and for a sufficient time to produce an alloyed layer on the surface of the cylinder bore having enhanced wear characteristics, as shown in Block  12  of FIG.  1 . During irradiation, the cylinder bore and the laser beam are moved relative to each other. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 is a block diagram depicting a first method of the present invention. 
     FIG. 2 is a block diagram depicting a second method of the present invention. 
     FIG. 3 is an enlarged front view of the laser beam cross sectional area on the surface of the cylinder bore when practicing the method of the present invention. 
     FIG. 4 is a side view of a first laser beam delivery system suitable for use in practicing the present invention. 
     FIG. 5 is an interior view of the cylinder bore during the irradiating step of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention comprises coating the interior surface of the cylinder bore with a precursor layer  21  comprising alloying elements that will result in enhanced wear characteristics when alloyed with the surface of the cylinder bore as shown in Block  10  of FIG.  1 . In a preferred embodiment, the precursor comprises iron, tin, copper, zirconium, titanium, zirconium-carbide, titanium-carbide, titanium-diboride, molybdenum, molybdenum-disilicide, molybdenum-disulfide, tungsten-carbide, nickel, aluminum, silicon, or silicon-carbide. In another preferred embodiment, the precursor may comprise encapsulated lubricant particles. In another preferred embodiment, the precursor comprises aluminum, silicon, and copper powder. The precursor layer has a thickness in the range of 50-150 microns. 
     In a preferred embodiment, the cylinder bore is machined prior to the application of the binder, as shown in Block  32  of FIG.  2 . In a preferred embodiment, this machining is performed with a cylindrical surfacing machine, such as a Mapol machine. In a preferred embodiment, this machining is carried out until the root mean square (rms) roughness of the bore surface is less than one micron. 
     The invention further comprises irradiating the cylinder bore surface with a laser beam  22  at a sufficient energy level and for a sufficient time to produce an alloyed layer on the surface of the cylinder bore having enhanced wear characteristics, as shown in Block  12  of FIG.  1 . In a preferred embodiment, the entire surface of the cylinder is irradiated. 
     During the irradiation of the cylinder bore, the cylinder bore and the laser beam are moved relative to each other along a translation axis  30 , as shown in FIG.  3 . Irradiation is performed in a series of parallel tracks  52  on the surface of the cylinder bore, as shown in FIG.  5 . In a preferred embodiment, the irradiation which forms each track begins in the bore at the lower end of the track and moves upward to the cylinder bore rim. In a preferred embodiment, each track has a length differential  54  from its adjacent track, as shown in FIG.  5 . As a result of this length differential, a toothlike pattern  56  is formed by the lower ends of adjacent tracks. 
     In a preferred embodiment, the cylinder surface and the laser beam are moved relative to each other at a translation rate in the range of 4000-9000millimeters per minute and the irradiation is performed at a laser power density in the range of 50 to 150 kilowatts/cm 2 . In another preferred embodiment the translation rate is 4500 millimeters/minute. 
     In a preferred embodiment, the irradiation is performed with a 3 kilowatt Nd:YAG laser  44  passed through a fiber optic delivery system  46  to a lens assembly  47 , which focuses the beam onto the cylinder bore surface. As shown in FIG. 4, the laser beam is directed to the surface of the cylinder bore at an acute angle. As also shown in FIG. 4, in a preferred embodiment, the laser beam is directed to the surface of the cylindrical bore in a straight trajectory. In a preferred embodiment, the laser beam is directed at a  35  degree angle to the surface of the cylinder bore, as shown in FIG.  4 . 
     In a preferred embodiment, the present invention further comprises directing a shielding gas  26  at the region of the surface being irradiated by the beam, as shown in Block  14  of FIG.  1 . In a preferred embodiment, the shielding gas is nitrogen or argon. 
     In a preferred embodiment, the laser beam has a rectangular cross sectional area  22 , as shown in FIG.  3 . This rectangular cross sectional area comprises two shorter sides  23  and two longer sides  24  as shown in FIG.  3 . In a preferred embodiment, the longer sides of the rectangular cross sectional area of the laser beam are perpendicular to the translation axis  30  of the beam relative to the piston, as shown in FIG.  3 . 
     In another preferred embodiment, the longer sides of the rectangular cross sectional area have a length of at least 3.5 millimeters and the shorter sides of the rectangular cross sectional area have a length of at least 0.75 millimeters. A rectangular beam profile having the dimensions described above can be achieved by aligning a spherical lens closest to the beam, a second cylindrical lens closest to the substrate and a first cylindrical lens between the spherical lens and the second cylindrical lens. The spherical lens should have a focal length of 101.6 millimeters the first cylindrical lens should have a focal length of 203.2 millimeters. The second cylindrical lens should have a focal length of 152.4 millimeters. The spherical lens and the first cylindrical lens should be spaced apart by five millimeters. The first cylindrical lens and second cylindrical lens should be spaced apart 25 millimeters. 
     In a preferred embodiment where the cylinder bore is made from wrought aluminum, the laser beam used for irradiating has a power density of 125 kilowatts/cm 2 . In another embodiment where the cylinder bore is made from cast aluminum, the laser beam used for irradiating has a power density of 75 kilowatts/cm 2 . 
     The foregoing disclosure and description of the invention are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative embodiments may be made without departing from the spirit of the invention.