Adhesion and corrosive delamination of epoxy films on chemically etched ZnMgAl‐alloy coatings

Abstract

The effect of alkaline and acidic pretreatment steps on the surface chemical composition and adhesion properties of ZnMgAl‐alloy coated steel was investigated by means of spectroscopic methods, scanning Kelvin probe (SKP) and peel test measurements. The spectroscopic results indicate that the surface film composition can be adjusted by the wet‐chemical treatment. To study the corresponding surface adhesive properties, the samples were coated with an epoxy amine adhesive. Peel tests under humid conditions indicated an increased interaction between the acidic pre‐treated surface and the adhesive. The results of the SKP analysis show that the acidic cleaned substrates have the highest resistance to delamination, which can be explained by the shift of the interfacial electrode potential.

Effect of surface roughness and chemistry on the adhesion and durability of a steel-epoxy adhesive interface

“…Besides the effect of increased surface area and mechanical interlocking, the acid treatment could also alter the type and number of interactions between the adhesive and the substrate. According to Pohl et al acid treatments can lower the hydroxyl fraction at the surface, thereby promoting strong Lewis acid-base interactions between the acidic metal and the basic amino groups in the epoxy adhesive [34]. Since no traces of nitrogen of phosphor were found in the EDS, a possible contribution to the improved adhesion by incorporated phosphates or nitrates can be excluded.…”

“…The shape of the potential profile for the 80-grit sample is similar to the polished and silane-treated samples, but the inhibiting effect on delamination front movement is less profound as is the case for the silane-treated samples. The shape of these potential profiles has been designated as typical for a cathodic delamination mechanism on steel [34,37,44] thereby indicating that cathodic delamination is the responsible delamination mechanism for this system.…”

Archives of Metallurgy and Materials

“…The mg and al components in the coating layer dissolve in corrosive environments to promote the formation of compact and dense corrosion products, such as simonkolleite (Zn 5 oh 8 Cl 2 h 2 o) and layered double hydroxides, thereby significantly enhancing the barrier effect [7][8][9]. in addition to optimizing the alloying composition, various surface-treatment methods, such as conversion coating [10,11], chemical treatment [12], and plasma treatment [13,14], which utilize the electrochemically active characteristics of al and mg, have been used to improve the physical properties of the Zn-mg-al (Zma) coating layer. atmospheric pressure (aP) plasma treatment has gained immense attention because the reactive radicals in the system can be effectively used for cleaning or altering the surface roughness by modifying the physical and/or chemical properties of material surfaces.…”

Scanning Kelvin probe blister studies of the delamination of epoxy films on organosilane modified ZnMgAl alloy coated steel

“…Giza et al showed that the surface potential of an MgZn 2 alloy can be adjusted by applying reducing and oxidizing plasma treatments . Pohl et al performed mild‐alkaline and acidic etching pre‐treatments on ZnMgAl‐alloy coatings for increasing the adhesion between the Zn coating and the epoxy amine adhesives . Yasaku et al investigated the effect of different stripping/cooling atmospheres used during the galvanizing process on the surface composition, localized corrosion, and adhesion strength .…”