Coating film and metal 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 . A coating film in which a powder is deposited by powder-coating on 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 performed simultaneously to form the coating film on the surface of the metal automotive part;
 said coating film for a metal automotive part being characterized in that the surface of the metal automotive part before the powder is deposited thereon is a work-hardened basis material surface that has not been subjected to a chemical conversion film treatment.   
     
     
         2 . The coating film for metal automotive parts according to  claim 1 , 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. 
     
     
         3 . The coating film for a metal automotive part according to  claim 1 , characterized in that the basis material surface has been cleaned using an alkaline detergent. 
     
     
         4 . The coating film for a metal automotive part according to  claim 1 , 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. 
     
     
         5 . The coating film for a metal automotive part according to  claim 1 , characterized in that the quenching is high-frequency quenching, and tempering and powder bake-hardening are carried out by high-frequency induction heating. 
     
     
         6 . The coating film for a metal automotive part according to  claim 1 , characterized in that the powder is a pulverulent epoxy-based powder coating composition. 
     
     
         7 . The coating film for a metal automotive part according to  claim 6 , characterized in that the powder is a pulverulent coating composition comprising a bisphenol A epoxy resin, a hydrazide compound, and an inorganic filler. 
     
     
         8 . The coating film for a metal automotive part according to  claim 7 , characterized in that the hydrazide compound is an organic acid polyhydrazide. 
     
     
         9 . The coating film for a metal automotive part according to  claim 7 , characterized in that the inorganic filler is barium sulfate. 
     
     
         10 . A metal automotive part having a coating film formed on a surface, said metal automotive part characterized in that the coating film is the coating film for a metal automotive part according to  claim 1 , and the metal automotive part is an outer joint member constituting a constant velocity universal joint, or an intermediate shaft constituting a drive shaft. 
     
     
         11 . The metal automotive part according to  claim 10 , 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. 
     
     
         12 . A constant velocity universal joint comprising an outer joint member, an inner joint member, a drive shaft that is linked to the inner joint member, and a boot that is mounted, directly or via another member, on the outer joint member and the drive shaft, said constant velocity universal joint characterized in that an intermediate shaft that constitutes the outer joint member and/or drive shaft is the metal automotive part according to  claim 10 .