Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/28—Selection of soldering or welding materials proper with the principal constituent melting at less than 950 degrees C
  • B23K35/286—Al as the principal constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest

Definitions

• This invention relates to a method for modifying the surface of an aluminum or aluminum alloy substrate, as well as to a coating mixture used in the method, a coated substrate surface and a modified surface product.
• Japanese Published Application 59-219468 (Teikoku Piston Ring K.K.) describes a method for
• EP-A 0 036 594 (Union Carbide Corporation), published September 30, 1981 describes a process for making porous the surface of aluminum substrates by coating the substrate with finely divided powder of aluminum alloy, aluminum-silicon alloy to act as the bonding component, and a flux, preferably of the potassium fluoaluminate type. This technique requires the use of the aluminum-silicon alloy binding agent which is a separate preformed aluminum brazing alloy powder.
• British Patent 234,969 (L.D. Hooper) teaches that any surface can be siliconized by making a preparatory deposit of a more receptive substance such as Pb, Sn, Cu, or Al in a known manner, or a flux may be incorporated with the silicon such as an alkali metal or its halide, aluminate, borate, oxide or hydroxide or aluminum or zinc halide.
• brazing as used within the context of the present invention is not restricted to the joining of workpieces.
• brazing temperature a temperature at which the brazing alloy melts while the components remain unmelted.
• the brazing alloy forms a fillet or joint that bonds the joining surfaces of the components.
• the melting point of the brazing alloy be at least 30o to 40oC lower than that of the metal of the components.
• An example of a suitable aluminum brazing alloy is an Al-Si eutectic composition, which melts at about 577oC.
• a eutectic is formed in situ with the aluminum by the application of the coating to the surface of the aluminum and then heating this coating material.
• the novel coating mixture may be applied either as a dry powder or as a slurry, preferably in a volatile liquid carrier, which may be water based or based on an organic substance, such as alcohol. It may also be applied as a paste made with an organic or other binder which is volatilized at the
• the preferred metal component of the coating mixture to provide the eutectic alloy is silicon but other metals such as zinc, copper or germanium may be used.
• metal refers to the elemental form of a metal, as commercially available in unalloyed form, which may include small concentrations of impurities which do not affect its characteristics.
• the main requirement is that there be present in the coating mixture a metal component which at brazing temperatures is capable of dissolving in the aluminum and forming in situ with the aluminum a layer of brazeable eutectic alloy.
• the flux component of the coating mixture may be any material capable of removing the oxide layer and which melts below 600oC.
• the preferred flux is a complex
• Aluminum brazing fluxes are: mixtures of alkali and alkaline earth chlorides and fluorides, ammonium chloride, ammonium fluoride, potassium acid fluoride (KHF 2 ), sodium acid fluoride (NaHF 2 ), ammonium acid fluoride (NH 4 HF 2 ), zinc chloride, mixtures of zinc chloride, potassium acid fluoride and ammonium chloride and potassium fluoro- zirconate (K 2 ZrF 6 ).
• the metal component and flux are typically present in the mixture in a ratio (wt/wt) of metal component to flux in the range of 0.1:1 to 5:1, preferably 0.25:1 to 0.5:1.
• the metal component capable of forming a brazable eutectic with aluminum is preferably in the form of fine particles having sizes less than 10% of the thickness of the substrate, e.g. in the range of dimensions from about 1 to 1000 ⁇ m, preferably 4 to 80 ⁇ m, more preferably 5 to 50 ⁇ m, with a range of 10 to 20 ⁇ m being particularly preferred.
• the surface modifying particulate material component of the coating mixture is typically present in an amount of up to 1 part by weight per 1 part by weight of the eutectic forming metal of the coating mixture, but even higher and lower ratios may be used. This may be as high as 6 parts particulate material per 1 part eutectic forming metal.
• the coating mixture may also include a binder component.
• This binder may be selected from a variety of binder materials which are capable of volatilizing below the melting point of the flux and the eutectic alloy.
• suitable binder materials include a mixture polyethylmethacrylate and butylacrylate or 1-(2-methoxy-1-methyloxy)-2-propanol and propylene glycol as the carrier, or 2-methyl-2,4-pentanediol.
• the amount of coating mixture applied to the surface is usually less than 130 g/m 2 , with a range of about 30 to 100 g/m 2 being preferred.
• a binder is included in the mixture, as much as 130 g/m 2 can be applied.
• a mixture without a binder should not be applied in an amount above 100 g/m 2 .
• a wide range of different powdered materials may be used as the modifying material. These are typically metals, ceramic materials or refractory materials, but preferably comprise powders selected from the group consisting of nickel, iron, manganese, cobalt, chromium, copper, titanium, boron nitride, nickel aluminide, metal borides, metal suicides such as tungsten silicide or chromium silicide, metal carbides such as tungsten carbide or silicon carbide, metal nitrides or metal oxides. These are preferably used in the form of powders and typically have particle sizes in the range of 1 to 150 ⁇ m.
• the joining procedure of the invention is preferably carried out at a temperature in the range of 420 to
• the temperature required is between 580 and 650oC.
• the quality of the brazed layer depends upon the relative Si/flux content in the brazing mixture and on the surface coverage by that mixture and the length of time held at the brazing temperature.
• the in situ formation of the eutectic Al-Si alloy occurs through the complementary actions of the flux material and the silicon. For instance, at 600oC the flux is molten and dissolves or removes the native oxide film on the aluminum surfaces being treated, exposing fresh aluminum to the silicon powder. Because of the high solubility of silicon in aluminum at this temperature, the silicon dissolves rapidly into the exposed aluminum surface, forming a surface layer of liquid Al-Si alloy with a composition believed to be close to the Al/Si eutectic of 89% Al/11% Si in the aluminum substrate.
• the silicon-containing aluminum surface melts and flows in the temperature range 577 to 650oC. It is believed that the molten flux reduces the surface tension of the molten Si/Al eutectic alloy so that the molten alloy forms around the modifying particles. Because the formation of the
• Al/Si eutectic alloy depends on diffusion of silicon into aluminum, the brazing process must be carried out at the above temperature for a time interval sufficiently long for Si-diffusion and for the ensuing alloy-forming to occur. This time interval typically ranges from about 0.1 to 10 minutes, preferably 1 to 7 minutes.
• Fig. 1 is a photomicrograph of a flux:silicon:nickel modified surface
• Fig. 2 is a photomicrograph of a
• Fig. 3 is a photomicrograph of a flux: silicon:niobium modified surface
• Fig. 4 is a photomicrograph of a flux:silicon: silicon carbide modified surface.
• a substrate alloy consisting of AA1100 aluminum alloy was sheared into 25 mm ⁇ 3 mm ⁇ 1 mm coupons.
• the coupons were cleaned by swabbing in acetone followed by caustic etching for 10 seconds in 5 % w/w, 65oC sodium hydroxide solution, desmutted in 50% nitric acid, water rinsed and forced air dried.
• the slurries were prepared at 50% total solids in isopropyl alcohol with a silicon: flux powder ratio of 1:3:0.65. Silicon powder 50 ⁇ m median particle size and Nocolok ® KC 100 flux, a potassium fluoroaluminate flux, were used to prepare the slurries.
• a variety of different powders were added and the coated coupons were brazed horizontally in a brazing furnace using a rapid heat-up to 605°C and soaked at 605oC for 5 minutes,
• Table 1 lists the loading of each component on the various coupons.
• each of the modifying powders combined with the in situ formed Al-Si eutectic alloy resulted in a unique surface.
• the modifying powder appeared to be totally embedded in the Al-Si eutectic and this can be seen in Figure 2 where tungsten carbide was used as the powder.
• the modifying powder reacted in part to form intermetallics and this is shown in Figure 1 where nickel powder was used as the metal powder. Niobium was almost completely embedded in the Al-Si eutectic alloy as shown in Figure 3 and
• photomicrograph are not loose on the surface, but are held or are embedded in a eutectic alloy layer and cannot normally be rubbed or scraped off.
• a lower friction coefficient corresponds to a more wear resistant surface.
• the modified surfaces are also characterized by the amount of wear on the steel pin and the substrate.
• the Mn and Fe modified surfaces have friction coefficients of 0.1- 0.15 and 0.3 respectively.
• the amount of substrate wear on the Mn surface ranges from light to severe whereas substrate wear on the Fe surface is undetectable and consequently is more wear resistant.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical Treatment Of Metals (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (3)

Cited By (6)

Citations (6)

• 1992
  • 1992-10-23 WO PCT/CA1992/000465 patent/WO1993008952A1/en active Application Filing
  • 1992-10-23 AU AU27945/92A patent/AU2794592A/en not_active Abandoned
  • 1992-10-27 MX MX9206180A patent/MX9206180A/es unknown

Patent Citations (6)

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