Treatment method using zinc phosphate-free treatment agent that includes cationic urethane resin, and treated automobile component

Abstract

Provided is a coating pre-treatment method that does not limit the coating method, has a small impact on the environment, and can ensure good post-coating corrosion resistance in a hot-rolled steel sheet. A coating pre-treatment method in which a hot-rolled steel sheet is treated with a chemical conversion treatment agent to form a chemical conversion coating film, wherein the chemical conversion treatment agent includes at least one type (A) of element selected from the group consisting of zirconium, titanium, and hafnium, at least one type (B) of substance selected from the group consisting of amino group-including silane coupling agents, hydrolysates thereof, and polymers thereof, fluorine (C), and a cationic urethane resin (D), and the content of (A) is 20-600 mass ppm in total in terms of metals, and the pH is 3.5-5.5.

1 . A pre-coating treatment method, comprising: treating a hot-rolled steel sheet with a chemical conversion treatment agent to form a chemical conversion film, wherein the chemical conversion treatment agent includes
 at least one (A) selected from the group consisting of zirconium, titanium, and hafnium,   at least one (B) selected from the group consisting of an amino group-containing silane coupling agent, hydrolysates thereof, and polymers thereof,   fluorine (C), and   a cationic urethane resin (D), and   wherein the total content of (A) is 20 to 600 ppm by mass in terms of metal, and pH is 3.5 to 5.5.   
     
     
         2 . The pre-coating treatment method according to  claim 1 , wherein the total content of (B) is 5 to 1000 ppm by mass in terms of a solid content concentration,
 the content of (D) is 5 to 1000 ppm by mass in terms of a solid content concentration, and   the solid content mass ratio ((B)/(D)) of (B) to (D) is 0.005 to 200.   
     
     
         3 . The pre-coating treatment method according to  claim 1 , wherein the chemical conversion treatment agent further includes at least one adhesiveness and corrosion resistance-conferring agent selected from the group consisting of magnesium ions, zinc ions, calcium ions, aluminum ions, gallium ions, indium ions, and copper ions. 
     
     
         4 . A hot-rolled steel sheet treated with the pre-coating treatment method according to  claim 1 .