Automobile part and method for manufacturing automobile part

Abstract

[Object] There are provided automobile parts and a method for manufacturing the automobile parts. The automobile parts have an excellent corrosion resistance after coated with a electrodeposition paint with smaller thickness, improve formability and productivity in hot pressing, and also improve chemical conversion treatability after hot press-forming. [Solution] An automobile part according to the present invention includes: a formed steel sheet having an intermetallic compound layer formed on a surface of the steel sheet, the intermetallic compound layer being formed of Al—Fe intermetallic compound having a thickness of 10 μm or more and 50 μm or less, the intermetallic compound layer including a diffusion layer positioned in closest proximity to the steel sheet, the diffusion layer having a thickness of 10 μm or less; a surface coating layer provided on a surface of the intermetallic compound layer, the surface coating layer including a coating containing ZnO and a zinc phosphate coating and having a surface roughness of 3 μm or more and 20 μm or less as a maximum profile height Rt in accordance with JIS B0601 (2001); and an electrodeposition paint film provided on a surface of the surface coating layer and having a thickness of 6 μm or more and less than 15 μm.

1 . A method for manufacturing an automobile part, the method comprising:
 using an Al plated steel sheet including a coating containing ZnO on a surface of the Al plated steel sheet;   using a hot pressing method;   causing an Al plating layer having an average primary crystal diameter of 4 μm or more and 40 μm or less to have an amount of plating of 30 g/m 2  or more and 110 g/m 2  or less for one surface;   causing a ZnO amount of the coating containing ZnO to be 0.3 g/m 2  or more and 3 g/m 2  or less in metallic Zn equivalent for one surface;   causing a rate of temperature increase during a heating process in hot pressing to be 12° C./second or more;   causing a reaching steel sheet temperature to be 870° C. or more and 1100° C. or less; and   causing a electrodeposition paint film to have thickness of 6 μm or more and less than 15 μm.   
     
     
         2 . The method for manufacturing an automobile part according to  claim 1 , wherein an amount of the Al plating layer is 50 g/m 2  or more and 80 g/m 2  or less for one surface. 
     
     
         3 . A method for manufacturing a high-strength automobile part, the method comprising:
 using an Al plated steel sheet including a coating containing ZnO on a surface of the Al plated steel sheet;   using a hot pressing method;   causing an Al plating layer having an average primary crystal diameter of 4 μm or more and 40 μm or less to have an amount of plating of 30 g/m 2  or more and less than 60 g/m 2  for one surface;   causing a ZnO amount of the coating containing ZnO to be 0.3 g/m 2  or more and 3 g/m 2  or less as metallic Zn for one surface;   causing a rate of temperature increase during a heating process in hot pressing to be less than 12° C./second;   causing a reaching steel sheet temperature to be 850° C. or more and 950° C. or less; and   causing an electrodeposition paint film to have thickness of 6 μm or more and less than 15 μm.   
     
     
         4 . The method for manufacturing an automobile part according to  claim 3 , wherein an amount of the Al plating layer is 35 g/m 2  or more and 55 g/m 2  or less for one surface. 
     
     
         5 . A method for manufacturing a high-strength automobile part, the method comprising:
 using an Al plated steel sheet including a coating containing ZnO on a surface of the Al plated steel sheet;   using a hot pressing method;   causing an Al plating layer having an average primary crystal diameter of 4 μm or more and 40 μm or less to have an amount of plating of 60 g/m 2  or more and 110 g/m 2  or less for one surface;   causing a ZnO amount of the coating containing ZnO to be 0.3 g/m 2  or more and 3 g/m 2  or less as metallic Zn for one surface;   causing a rate of temperature increase during a heating process in hot pressing to be less than 12° C./second;   causing a reaching steel sheet temperature to be 920° C. or more and 970° C. or less; and   causing a electrodeposition paint film to have thickness of 6 μm or more and less than 15 μm.   
     
     
         6 . The method for manufacturing an automobile part according to  claim 5 , wherein an amount of the Al plating layer is 60 g/m 2  or more and 90 g/m 2  or less for one surface. 
     
     
         7 . The method for manufacturing an automobile part according to  claim 1 , wherein the content of ZnO is 0.5 g/m 2  or more and 1.5 g/m 2  or less in metallic Zn equivalent for one surface. 
     
     
         8 . The method for manufacturing an automobile part according to  claim 3 , wherein the content of ZnO is 0.5 g/m 2  or more and 1.5 g/m 2  or less in metallic Zn equivalent for one surface. 
     
     
         9 . The method for manufacturing an automobile part according to  claim 5 , wherein the content of ZnO is 0.5 g/m 2  or more and 1.5 g/m 2  or less in metallic Zn equivalent for one surface. 
     
     
         10 . The method for manufacturing an automobile part according to  claim 1 , wherein the Al plating layer has an average primary crystal diameter of 4 μm or more and 30 μm or less. 
     
     
         11 . The method for manufacturing an automobile part according to  claim 3 , wherein the Al plating layer has an average primary crystal diameter of 4 μm or more and 30 μm or less. 
     
     
         12 . The method for manufacturing an automobile part according to  claim 5 , wherein the Al plating layer has an average primary crystal diameter of 4 μm or more and 30 μm or less. 
     
     
         13 . The method for manufacturing an automobile part according to  claim 1 , further comprising:
 treating the Al plated steel sheet with chemical conversion by using a chemical conversion liquid containing phosphates, before hot pressing.   
     
     
         14 . The method for manufacturing an automobile part according to  claim 3 , further comprising:
 treating the Al plated steel sheet with chemical conversion by using a chemical conversion liquid containing phosphates, before hot pressing.   
     
     
         15 . The method for manufacturing an automobile part according to  claim 5 , further comprising:
 treating the Al plated steel sheet with chemical conversion by using a chemical conversion liquid containing phosphates, before hot pressing.