Controlling Void Contents in the Zn Interlayer for Improving Adhesion Strength of ZnMg/Zn Bilayer Coatings on TRIP Steel

Abstract

For ZnMg production feasibility, the adhesive strength of ZnMg alloy coatings must be raised to the level of commercial EG or GI steels. In this study, ZnMg/Zn bilayer coatings with various void contents in the Zn interlayer were synthesized using electromagnetic heating deposition, and the adhesion strength of ZnMg/Zn bilayer coatings on TRIP steels was investigated. As the input current during deposition decreased, the density of the Zn interlayer decreased from 83.2% to 93.2%, and the preferred orientation of the Zn interlayer changed from (101) to (002). During the ZnMg deposition on top of the Zn interlayer, a similar preferred orientation was observed in the ZnMg/Zn bilayer coating. A lap shear test result showed that the adhesion strength of ZnMg/Zn bilayer coatings increased from 19.1 MPa to 21.7 MPa as the (002) texture became dominant with decreasing void contents in the Zn interlayer. These adhesion strength results above 19 MPa were higher than those of the Zn coatings in the commercial EG and GI steels, suggesting that an additional improvement in the adhesion strength of the Zn–Mg/Zn bilayer coatings was possible by controlling the void contents in the Zn interlayer.