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-µm 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.