Effect of a Zn Interlayer on the Adhesion Strength and Corrosion Resistance of Zn-Mg Coated TRIP Steel

Zn-Mg coatings with Mg compositions ranging from 5 wt.% to 15 wt.% were synthesized on high strength steels using the electro-magnetic heating deposition process, and the effects of a 1-mu m thick Zn interlayer on the formability and adhesion of the Zn-Mg coatings were investigated. The Zn-Mg coatings with the Zn interlayer showed little difference in terms of microstructure, crystal structure and corrosion resistance compared to the Zn-Mg coatings without the Zn interlayer. In contrast, the Zn interlayer significantly contributed to the improvement of the formability and adhesion of the Zn-Mg coating. The delamination area of the Zn-Mg coating with the Zn interlayer after deformation was extensively reduced, and the results of the lap shear tests revealed that the maximum adhesion strength of the Zn-Mg coatings with the Zn interlayer was approximately twice as high as that of the Zn-Mg coatings without the Zn interlayer. The maximum adhesion strength of the Zn/Zn-Mg coatings with 15 wt.% Mg, which showed the best corrosion resistance was measured to be slightly over 10 MPa, pending more research to increase the adhesion strength of the Zn-Mg coatings with high content of Mg over approximately 20 MPa necessary.