Surface pre-treatment method for pre-coated heat-treatable, precipitation-hardenable stainless steel ferrous-alloy components and components coated thereby

Abstract

The present invention relates to the use, in a pre-coating process, of a flash plating, without a subsequent chromate seal, as a surface pre-treatment for a ferrous-alloy substrate prior to applying a corrosion-inhibiting coating to improve the overall corrosion protection of the pre-treatment component. Preferably the ferrous alloy is a heat-treatable, precipitation-hardenable stainless steel and the pre-treatement is a cadmium flash plate or a zinc-nickel alloy flash plate.

That which is claimed:  
     
         1 . A method for coating a ferrous-alloy aircraft structural component comprising the steps of: 
 providing an aircraft structural component made from a ferrous-alloy precursor having a pre-determined treatment temperature;    providing a flash plate pre-treatment;    subjecting the component to the flash plate pre-treatment;    providing a curable organic coating material having a non-volatile portion that is curable at about the pre-determined ferrous-alloy heat-treatment temperature;    applying the coating material to the component; and    substantially simultaneously curing the coating and the component by heat-treating the ferrous-alloy precursor to a pre-determined heat-treatment temperature.    
     
     
         2 . The method of  claim 1 , wherein the ferrous-alloy precursor is a heat-treatable, precipitation-hardenable stainless steel.  
     
     
         3 . The method of  claim 1 , wherein the pre-determined heat-treatment temperature is selected to substantially simultaneously cure the ferrous-alloy precursor and the organic coating.  
     
     
         4 . The method of  claim 1 , wherein the flash plate pre-treatment is selected from the group consisting of a cadmium flash plate and a zinc-nickel alloy flash plate pre-treatment.  
     
     
         5 . The method of  claim 1 , wherein the flash plate pre-treatment applies a flash plating to the component to a thickness of from about 0.0002 inch to about 0.0004 inch.  
     
     
         6 . The method of  claim 1 , wherein the flash plate pre-treatment does not comprise a subsequent chromate seal treatment.  
     
     
         7 . The method of  claim 1 , wherein the curing step treats the coated, ferrous-alloy component to impart pre-determined metallurgical properties to the ferrous-alloy material, and concurrently cure the coating.  
     
     
         8 . The method of  claim 1 , wherein the ferrous-alloy precursor is selected from the group consisting of 18-8, 17-4 PH, 17-7 PH, 15-5 PH, PH 13-8Mo, PH 15-7Mo, A-286, Custom 450, and Haynes 556 materials.  
     
     
         9 . The method of  claim 1 , wherein the ferrous-alloy precursor is A-286 alloy.  
     
     
         10 . The method of  claim 1 , wherein the coating is applied to the ferrous-alloy by a method selected from the group consisting of dipping, spraying, brushing, and fluidized-bed deposition.  
     
     
         11 . The method of  claim 1 , further comprising the step of snap tempering the ferrous-alloy precursor before the flash plate pre-treatment step.  
     
     
         12 . The method of  claim 1 , further comprising a ferrous alloy hardening treatment step wherein the hardening treatment step comprises austenitizing or normalizing the ferrous-alloy precursor.  
     
     
         13 . The method of  claim 1 , wherein the aircraft structural component is selected from the group consisting of fasteners, fittings, hinges, bearings, gears, struts, and the mechanical structures attached thereto.  
     
     
         14 . The method of  claim 1 , wherein the organic coating material comprises an organic, phenolic resin mixed with at least one plasticizer and an inorganic additive selected from the group consisting of aluminum powder and strontium chromate.  
     
     
         15 . The method of  claim 1 , wherein the organic coating material comprises polytetrafluoroethylene.  
     
     
         16 . The method of  claim 1 , wherein the organic coating material is dissolved in a solvent selected from the group consisting of ethanol, toluene, methyl ethyl ketone (MEK), and mixtures thereof.  
     
     
         17 . The method of  claim 1 , wherein the organic coating material comprises a sprayable solution having about 30 weight percent ethanol, about 7 weight percent toluene, about 45 weight percent methyl ethyl ketone (MEK), about 2 weight percent aluminum powder and about 2 weight percent strontium chromate.  
     
     
         18 . The method of  claim 16 , further comprising the step of exposing the coated component to a temperature of from about 180° F. to about 220° F. for about two minutes to liberate the solvent from the coating.  
     
     
         19 . The method of  claim 1 , wherein the organic coating material is applied to the component to a thickness of from about 0.0003 inch to about 0.0005 inch.  
     
     
         20 . A method for improving the corrosion protection of a ferrous-alloy substrate comprising the steps of: 
 providing a ferrous-alloy substrate;    applying to the ferrous-alloy substrate a flash plate pre-treatment without a subsequent chromate seal treatment; and    applying a curable organic coating material having a non-volatile portion that is curable at about a pre-determined heat-treatment temperature of the ferrous alloy.    
     
     
         21 . The method of  claim 20 , wherein the ferrous alloy is a heat-treatable, precipitation-hardenable, stainless steel.  
     
     
         22 . The method of  claim 20 , wherein the flash plate pre-treatment is selected from the group consisting of cadmium flash plate and zinc-nickel alloy flash plate.  
     
     
         23 . A corrosion resistant aircraft structural ferrous-alloy component prepared according to a method comprising the steps of: 
 providing an aircraft structural component made from a ferrous-alloy precursor having a pre-determined heat-treatment temperature;    providing a flash plate pre-treatment without a subsequent chromate seal;    subjecting the component to the flash plate pre-treatment;    providing a curable organic coating material having a non-volatile portion that is curable at about the pre-determined ferrous-alloy heat-treatment temperature;    applying the organic coating material to the component to form a coated component; and    curing the coated component to a pre-determined temperature.    
     
     
         24 . The component of  claim 23 , wherein the ferrous-alloy precursor is a heat-treatable, precipitation-hardenable stainless steel.  
     
     
         25 . The component of  claim 23 , wherein the organic coating applied to the ferrous alloy and the ferrous alloy is heat-treated substantially simultaneously.  
     
     
         26 . The component of  claim 23  wherein the curable organic coating material is an organic, phenolic resin mixed with at least one plasticizer and an inorganic additive selected from the group consisting of aluminum powder and strontium chromate.  
     
     
         27 . The component of  claim 23 , wherein the coating material is dissolved in a solvent selected from the group consisting of ethanol, toluene, methyl ethyl ketone (MEK), and mixtures thereof.  
     
     
         28 . A ferrous-alloy aircraft structural component comprising: 
 a ferrous-alloy precursor having a pre-determined heat-treatment temperature;    a flash plate pre-treatment without a subsequent chromate seal; and    a curable, organic coating made from a material having a non-volatile portion that is curable at about the pre-determined ferrous-alloy heat-treatment temperature, wherein the precursor and the coating are substantially simultaneously heat-treated.    
     
     
         29 . The component of  claim 28 , wherein the ferrous-alloy precursor is a heat-treatable, precipitation-hardenable stainless steel.  
     
     
         30 . The component of  claim 28 , wherein the flash plate pre-treatment is deposited onto the precursor to a thickness of from about 0.0002 inch to about 0.0004 inch.  
     
     
         31 . The component of  claim 28 , wherein the organic coating is deposited onto the flash plate pre-treatment to a thickness of from about 0.0003 inch to about 0.0005 inch.  
     
     
         32 . The component of  claim 28 , wherein the precursor and organic coating are substantially simultaneously heat-treated to a temperature of from about 350° F. to about 400° F. for a duration of from about 4 hours to about 5 hours.  
     
     
         33 . The component of  claim 28 , wherein the flash plate pre-treatment is selected from the group consisting of cadmium flash plate and zinc-nickel alloy flash plate.  
     
     
         34 . The component of  claim 28 , wherein the ferrous-alloy precursor is selected from the group consisting of 18-8, 17-4 PH, 17-7 PH, 15-5 PH, PH 13-8Mo, PH 15-7Mo, A-286, Custom 450, and Haynes 556 materials.  
     
     
         35 . The component of  claim 28 , wherein the ferrous-alloy precursor is an A-286 alloy.  
     
     
         36 . The component of  claim 28 , wherein the aircraft structural component is selected from the group consisting of fasteners, fittings, hinges, bearings, gears, and struts.  
     
     
         37 . The component of  claim 28 , wherein the organic coating comprises a phenolic resin mixed with at least one plasticizer, and an inorganic additive selected from the group consisting of aluminum powder and strontium chromate.  
     
     
         38 . The component of  claim 28 , wherein the organic coating comprises polytetrafluoroethylene.  
     
     
         39 . The component of  claim 28 , wherein the organic coating is dissolved in a solvent selected from the group consisting of ethanol, toluene, methyl ethyl ketone (MEK), and mixtures thereof.  
     
     
         40 . The component of  claim 28 , wherein the organic coating comprises a sprayable solution having about 30 weight percent ethanol, about 7 weight percent toluene, about 45 weight percent methyl ethyl ketone (MEK), about 2 weight percent aluminum powder and about 2 weight percent strontium chromate.  
     
     
         41 . The component of  claim 39 , wherein the organic coated component is exposed to a temperature of from about 180° F. to about 220° F. for about two minutes to liberate the solvent from the coating.  
     
     
         42 . An aircraft comprising a ferrous-alloy aircraft structural component comprising: 
 a ferrous-alloy precursor having a pre-determined heat-treatment temperature, said precursor pre-treated with a flash plate pre-treatment deposited to a thickness of from about 0.0002 inch to about 0.0004 inch without a subsequent chromate sealant; and    a curable, organic coating made from a material having a non-volatile portion that is curable at about the pre-determined ferrous-alloy heat-treatment temperature, wherein the precursor and the coating are substantially simultaneously heat-treated.    
     
     
         43 . The aircraft of  claim 42 , wherein the ferrous alloy is a heat-treatable, precipitation-hardenable stainless steel.  
     
     
         44 . The aircraft of  claim 42 , wherein the flash plate pre-treatment is selected from the group consisting of cadmium flash plate and zinc-nickel alloy flash plate.  
     
     
         45 . The aircraft of  claim 42 , wherein the precursor and the coating are heat-treated to a temperature of from about 350° F. to about 400° F. for a duration of from about 4 hours to about 5 hours.  
     
     
         46 . The aircraft of  claim 42 , wherein the ferrous-alloy precursor is selected from the group consisting of 18-8, 17-4 PH, 17-7 PH, 15-5 PH, PH 13-8Mo, PH 15-7Mo, A-286, Custom 450, and Haynes 556 materials.  
     
     
         47 . The aircraft of  claim 42 , wherein the ferrous-alloy precursor is an A-286 alloy.  
     
     
         48 . The aircraft of  claim 42 , wherein the aircraft structural component is selected from the group consisting of fasteners, fittings, hinges, bearings, gears, struts, bolts, nuts, rivets, washers, springs, and screws.  
     
     
         49 . The aircraft of  claim 42 , wherein the organic coating comprises a phenolic resin mixed with at least one plasticizer, polytetrafluoroethylene and an inorganic additive selected from the group consisting of aluminum powder and strontium chromate.  
     
     
         50 . The aircraft of  claim 42 , wherein the aircraft structural component is exposed to a temperature of from about 180° F. to about 220° F. for about two minutes to liberate a solvent from the coating material.