Enhancement of Coating Features by Supporting ZincBased Coating with Cataphoresis Process: Effect of Acidity and Coating Thickness on the Coating Quality

Abstract

In this work, a cast material that is often used in the automobile sector was employed to produce cast elements with enhanced corrosion performance at low microns by combining two forms of cost-effective coatings (zinc + cataphoresis). In the context of the investigation, firstly 5-8 mu m or 12-15 mu m zinc-coating in an alkaline (Zn, Zn-Fe, Zn-Ni) or an acidic (Zn, Zn-Ni) environment, followed by 20-25 mu m cataphoresis-coating were performed on GGG40 cast-parts. Ink, hogaboom, shock, pull -off adhesion, water resistance, salt spray, stone impact, cyclic-corrosion, and scab-corrosion performance tests were implemented for characterization. In addition, the zinc-coating thickness and the phosphate-crystal appearance were evaluated in the x-ray diffraction laminography instrument and the scanning electron microscope. The tensile strengths were determined by the pull -off adhesion test between 171 and 433 psi. The coating thicknesses of zinc-coated parts in alkaline and acidic environments were assigned in the range of 5.887.18 mu m and 12.10-12.96 mu m. Due to the characterization results; it was deduced that the cataphoresis-coating after all zinc-basedcoatings under alkaline medium did not afford the required quality and corrosion protection, while cast parts coated under acidic medium before cataphoresis-coating gave appropriate corrosion performance, thus the low-cost coatings could be performed with the eligible properties.