Formation Behavior of Plating Films of Zn–V Composite Electroplated Steel Sheets and its Heat Dissipation Characteristics

The formation behavior of the plating films of Zn-V composite electroplated steel sheets was investigated using electrochemical techniques, and the paint adhesion and heat absorption/dissipation properties were investigated. In Zn-V composite plating, V compounds were preferentially deposited at the initial stage of plating, subsequently Zn was deposited in the form of an electric field-oriented fiber structure. As plating progressed, Zn-V composite plating films consisting of an electric field-oriented fiber structure of Zn and a non-electric field-oriented structure of V compounds were formed, and V compounds were codeposited in the gaps between Zn platelet crystals. The critical current density for initiating Zn plating was about 20 times higher in Zn-V bath than in Zn bath. In Zn-V bath, at the potential range more noble than that for initiating Zn plating, since V ions were reduced from tetravalent to trivalent along with the hydrogen evolution, the critical current density seems to be higher. The Zn-V composite plated steel sheets had better paint adhesion than EG. The excellent paint adhesion is attributed to the anchor effect caused by the large surface roughness and the formation of chemical bonds between the paint films and the oxide or hydroxide of V in the plating films. The Zn-V composite plated steel sheets had a higher emissivity than electrogalvanized steel sheets (EG). As a result, the emissivity after chemical conversion coating was high, and the sheets had high heat dissipation. This seems to be due to the oxide or hydroxide of V in the Zn-V plating films.