Effects of Mn and Ti on Microstructure and Corrosion Resistance of Hot-Dip Galvanized Zn-5Al Alloy Coatings

Effects of Mn and Ti on the microstructure and corrosion resistance of hot-dip galvanized Zn-5Al alloy coatings were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrochemical testing. The results indicate that the corrosion rates of Zn-5Al-0.2Mn and Zn-5Al-0.15Ti alloy coatings were 44.8% and 39% of that of Zn-5Al alloy coating, respectively. The addition of Mn and Ti in Zn-5Al alloy coating promoted the agglomeration of Al in transition zone, and increased the thickness of the transition layer containing Fe₂Al₅. The eutectic structure in Zn-5Al alloy coating was refined by additing Mn, and was coarsened by additing Ti, but the eutectic Al phase was continuously fused with the matrix of steel at this time. The Zn-5Al-0.2Mn and Zn-5Al-0.15Ti alloy coatings had smaller corrosion current densities than the Zn-5Al alloy coating, showing better corrosion resistance of the former.