Abstract
Abstract This study reports a “high temperature fast annealing” approach to tailor the microstructure of ZnMg–Zn bilayer coatings through a diffusion-driven phase transformation and to improve the adhesion strength and corrosion resistance, simultaneously. Selection of the appropriate annealing condition, 250 °C for 3 min, promotes the formation of MgZn2 on the topmost surface of the coating and Mg2Zn11 at the interface of ZnMg/Zn. This results to an increase of the adhesion strength from 65 MPa in the as-deposited condition to 82 MPa after annealing as well as a reduction in the corrosion current density from 0.91 to 0.52 μA/cm2, indicating enhanced corrosion resistance. The diffusion of the elements at high temperatures is also modeled to predict the stability region of phases during the annealing treatment. An excellent correlation is obtained between simulation and the experimental results.
Highlights
Zinc is a well-known protective coating for steels as it acts as a barrier layer and sacrificial anode against environmental corrosion [1]
The effect of “high temperature fast annealing” is studied on the adhesion strength and the corrosion resistance of ZnMgeZn bilayer coating with the aim of improving the coating properties
Fast annealing treatment of the as-deposited ZnMgeZn bilayer coating was performed using a ceramic heater with an ultrafast ramp rate up to 150 C/s
Summary
Zinc is a well-known protective coating for steels as it acts as a barrier layer and sacrificial anode against environmental corrosion [1]. Many efforts have been made to improve the corrosion resistance of zinc coated steels by the addition of alloying elements. These efforts led to the alloying with Mg and/or Al [2e5] which is feasible in an industrial scale. Different strategies can be utilized to improve the adhesion of ZnMg coatings to steels substrate. It includes the addition of a more ductile interlayer [7] and the modification of chemical composition [7]. The effect of “high temperature fast annealing” is studied on the adhesion strength and the corrosion resistance of ZnMgeZn bilayer coating with the aim of improving the coating properties
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