Effect of Sn Powder Content on Properties of Chromium-Free Zinc-Aluminum Coatings

Abstract

To further reduce the friction coefficient of zinc-aluminum coatings, tin (Sn) powder was introduced into waterborne chromium-free zinc-aluminum coatings. The coatings were evaluated and analyzed in terms of hardness, adhesion, impact resistance, salt spray resistance, electrochemical properties, friction coefficient and micro morphology. The impact of varying amounts of Sn powder on the mechanical properties, corrosion resistance and tribological performance of the coatings was investigated. Results showed that the introduction of tin powder into zinc-aluminum coatings effectively enhanced the toughness of the coatings. When the added amount of Sn powder was 5%～10% (mass fraction, the same below), the hardness of the coatings did not decrease, and both adhesion and impact resistance were significantly improved; the addition of Sn powder was also found to improve the lubrication performance of the coating, reducing its friction coefficient. When the content of Sn powder reached 10%～20%, both the thread friction coefficient and the support surface friction coefficient were reduced to below 0.15. More importantly, the introduction of Sn powder was found to enhance the corrosion resistance of the coating. Results from neutral salt spray tests and electrochemical testing indicated that the coatings exhibited relatively better corrosion resistance when the Sn powder content was 10%.

Keywords

• chromium-free zinc-aluminum coating|sn powder content|corrosion resistance|tribological properties|mechanical properties