Coating film and automotive part on which coating film is formed, and constant velocity universal joint

Abstract

The invention provides a coating film having excellent adhesion, even without a chemical conversion film treatment being carried out as an undercoat treatment, and a metal automotive part having the coating film. A powder is deposited by powder-coating onto the surface of a metal automotive part that has been quenched after forging, and tempering of the metal automotive part and bake-hardening of the deposited powder are carried out simultaneously, thereby forming a skin film on the surface of the metal automotive part. The surface of the metal automotive part before the powder is powder-coated thereon is a work-hardened basis material surface that has been not subjected to a chemical conversion filming treatment.

1 - 12 . (canceled) 
     
     
         13 . A method of forming a coating film on a surface of a metal automotive part, comprising:
 a powder-coating step in which a powder is deposited by powder-coating on the surface of the metal automotive part that has been quenched after forging, and   a tempering and bake-hardening step in which tempering of the metal automotive part and bake-hardening of the deposited powder are performed simultaneously,   wherein the surface of the metal automotive part before the powder is deposited thereon is a work-hardened basis material surface and   wherein in the powder-coating step, the powder is deposited on a surface which is the basis material surface, has not been subjected to a chemical conversion film treatment and has been cleaned using an alkaline detergent.   
     
     
         14 . The method of forming a coating film according to  claim 13 , characterized in that the basis material surface is a surface layer that has been quenched after forging, and a turned face in which a part of the surface layer has been turned. 
     
     
         15 . The method of forming a coating film according to  claim 13 , characterized in that the forging is cold forging, the surface hardness after cold forging is HRB 90 to 110, and the surface hardness after quenching is HRC 50 to 65. 
     
     
         16 . The method of forming a coating film according to  claim 13 , characterized in that the quenching is high-frequency quenching, and tempering and powder bake-hardening are carried out by high-frequency induction heating. 
     
     
         17 . The method of forming a coating film according to  claim 13 , characterized in that the powder is a pulverulent epoxy-based powder coating composition. 
     
     
         18 . The method of forming a coating film according to  claim 17 , characterized in that the powder is a pulverulent coating composition comprising a bisphenol A epoxy resin, a hydrazide compound, and an inorganic filler. 
     
     
         19 . The method of forming a coating film according to  claim 18 , characterized in that the hydrazide compound is an organic acid polyhydrazide. 
     
     
         20 . The method of forming a coating film according to  claim 18 , characterized in that the inorganic filler is barium sulfate. 
     
     
         21 . The method of forming a coating film according to  claim 13 , wherein the metal automotive part is an outer joint member constituting a constant velocity universal joint, or an intermediate shaft constituting a drive shaft. 
     
     
         22 . The method of forming a coating film according to  claim 21 , characterized in that the coating film on the outer joint member or the intermediate shaft has a thickness of 40 to 150 μm, a pencil hardness of H to 2H, and a corrosion resistance of 120 hr or greater as determined by a salt water spray test.