Effect of carbon on the corrosion and wear performance of Zn-phosphate layers

This work explains the possibility to enhance the performance of Zn-phosphate layers by the incorporation of functionalized carbon particles into the phosphating solution. The analysis focuses on both the wear behavior and the corrosion protection ability. The study reveals that the phosphate films created with the combination of ultrasonic vibration along with the carbon particles possess a more compact structure in spite of being thinner than the conventional coatings. The analysis by electrochemistry has proved the growth of a less porous phosphate which is more rapidly developed under the novel conditions. In addition, the incorporation of the carbon particles produces analogous hopeite content, as verified by electron microscopy, an important parameter to validate the coating stability. The reduction in the friction coefficient at the initial period of the pin-on-disk test, evidences the improved performance. The coatings prepared with carbon show enhanced wear resistance since the remaining coating after equivalent sliding distance is thicker compared to conventional coatings. It has been demonstrated that the carbon particles play a noteworthy role in the phosphating process, as they provide additional sites for the cathodic reaction assisting to the rapid development of a more dense film. (C) 2015 Elsevier Ltd. All rights reserved.