Unraveling the Formation Mechanism of a Hybrid Zr-Based Chemical Conversion Coating with Organic and Copper Compounds for Corrosion Inhibition

摘要

Corrosion protection is of great importance, since corrosion on metals and alloys happens in a wide range of applications and causes economic and environmental issues. Among various corrosion protection methods, chemical conversion coatings applied by a simple solution immersion process on different metals as a pretreatment has great advantages. The technique is easy to operate and economic. The resulting conversion coatings then act as an effective barrier to corrosion, as well as improving the adhesion between the metal/alloy substrate and the subsequent organic coating. As conventional chromate and phosphate conversion coating treatment has health and environmental issues, there is a strong motivation to develop novel environmentally friendly chemical conversion coatings with comparable functionality. Specifically, zirconium-based (Zr-based) conversion coatings created by immersing alloy substrates in hexafluorozirconic acid (H_2ZrF_6) solution is an outstanding candidate because of its lower operational cost and fast deposition, while offering good anti-corrosion and adhesion properties. Prior works of Zr-based conversion coatings have been focusing on further improving their anti-corrosion performance by controlling the coating deposition parameters including temperature, time, pH value and incorporating organic (silane, phosphonic acids) or inorganic (copper, cerium) compounds. In this study, a novel organic-inorganic hybrid Zr-based conversion coating with copper (Cu) and polyamidoamine (PAMAM). Incorporating organic component PAMAM has been shown to enhance the corrosion resistance of the conversion coating, as well as to provide binding media for the subsequent paint coating. Despite evidence showing superior performance, the film growth and reaction mechanisms of the hybrid conversion coatings, when incorporating these additives, is not well understood.