The Holes of Zn Phosphate and Hot Dip Galvanizing on Electrochemical Behaviors of Multi-Coatings on Steel Substrates

Abstract

The aim of this investigation is focused on the evaluation of distinctive coatings commonly applied in the automotive industry. The resulting corrosion behavior is analyzed by using electrochemical impedance spectroscopy (EIS), equivalent circuit (EC) and potentiodynamic polarization curves. The novelty concerns a comparison between tricationic phosphate (TCP), cataphoretic electrodeposition (CED) of an epoxy layer, TCP + CED and HDG (hot-dip galvanized) + TCP + CED multi-coatings. Both the naturally deposited and defect-induced damage (incision) coatings are examined. The experimental impedance parameters and corrosion current densities indicate that multi-coating system (HDG + TCP + CED layers) provides better protection. Both planar and porous electrode behaviors are responsible to predict the corrosion mechanism of the majority of samples examined. Although induced-damage samples reveal that corrosion resistances decreased up to 10×, when compared with no damaged samples, the same trend of the corrosion protection is maintained, i.e., TCP < CED < TCP + CED < HDG + TCP + CED. It is also found that the same trend verified by using electrochemical parameters is also observed when samples are subjected under salt spray condition (500 h). It is also found that porous electrode behavior is not a deleterious aspect to corrosion resistance. It is more intimately associated with initial thickness coating, while corrosion resistance is associated with adhesion of the CED layer on TCP coating. The results of relative cost-to-efficiency to relative coating density ratios are associated with fact that a CED coating is necessary to top and clear coating applications and the TCP + CED and the HDG/TCP + CED coating systems exhibit the best results.

Effect of Ni-MOF Derivatives on the Electrochemical Corrosion Behavior of Sn-0.7Cu Solders

“…It was noted that the potential scan rate had an important role in minimizing the effects of distortion in Tafel slopes and corrosion current density analyses, as previously reported [24][25][26]. However, based on these reports, the adopted 10 mV/s had no deleterious effects on the Tafel extrapolations in determining the corrosion current densities of the examined samples.…”

Testing the Mechanical Properties of High-Strength Zinc-Coated Bolts: FEM Approach

“…It should also be noted that as the zinc coating thickness increases, theoretically as the corrosion resistance increases, the stiffness of bolts may decrease. The conclusions drawn from the calculations warrant further research towards determining the effect of the thickness of different coatings (including multi-coatings [56]) applied to bolts of different sizes and using 3D FE models. One possible direction for such research is to determine a more detailed relationship between mechanical resistance and corrosion resistance of bolts.…”

Corrosion Inhibition of Mild Steel in Hydrochloric Acid Environment Using Terephthaldehyde Based on Schiff Base: Gravimetric, Thermodynamic, and Computational Studies

“…In Figure 9 , is the environment impedance; Rct is the charge-transfer impedance; signifies the double-layer constant-phase element; refers to the adsorbed-layer impedance; is the adsorbed-layer constant-phase element. Because an equivalent circuit is used to determine the simulated values and for comparison with experimental data, a CNLS (complex nonlinear least squares) simulation was used, as previously reported [ 44 , 45 , 46 ].…”