Adhesion Properties of Metallic Coatings on Mild Steel Substrates

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Adhesion properties of metallic coatings are always an interesting field of study. Therefore, to better understand the adhesion properties, three most applied pure metallic coatings, which were produced locally, have been selected for this study. Chromium (Cr), nickel (Ni) and zinc (Zn) coatings were purposely chosen for their wide industrial applications. The coatings were developed on the mild steel substrates using electroplating process and adhesion properties of these coatings were compared. Several parameters such as coating’s thickness, microstructure and hardness, substrates surface roughness and coating-substrate composite-hardness were studied. Two coating’s thickness categorized as thin and thick coatings and two substrate’s surface roughness named as smooth and rough were prepared. The adhesion properties of coatings were assessed by using the REVETEST scratch tester. The scratch tests were on the progressive load mode and the critical loads, Lc for each coating were determined by both acoustic emission signal and microscopic examination. Surface roughness test was conducted using the Mahr Perthometer PGK 120 surface profiler. Rockwell-Hardness tester was utilized for both substrates and composites (coating-substrate) hardness test. The correlation and relationship between the metallic coatings adhesion and the said parameters were established and highlighted. All the metallic coatings have shown improved surface roughness and composite-hardness of the substrates. Eventually, the metallic coatings were ranked based on their superiority in adhesion properties, where Cr was the best followed by Ni and Zn.