Effect of Al and Si on microstructure and corrosion resistance of hot dipping Zn-Al-Mg alloy coatings

The microstructure and properties of Zn-0.5Al-1.5Mg, Zn-2Al-1.5Mg and Zn-2Al-1.5Mg-0.3Si (mass fraction, %) alloy coatings were comparatively studied, and the effects of Al and Si on the microstructure and the corrosion resistance of hot dipping Zn-Al-Mg alloy coatings were investigated by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope, full immersion corrosion and neutral salt spray test. The results show that the composition phases of three alloy coatings are Zn, Al and MgZn2 phases. Zn-0.5Al-1.5Mg alloy coating is composed of bulk Zn-rich phase and Zn+MgZn2 eutectic structure at the grain boundary, Zn-2Al-1.5Mg alloy coating is composed of bulk Zn-rich phase and Zn+Al+MgZn2 eutectic structure at the grain boundary, Zn-2Al-1.5Mg-0.3Si alloy coating is composed of bulk Zn-rich phase, Zn+Al+MgZn2 eutectic structure at the grain boundary and acicular Mg2Si. The Al, Mg and Si distribute mainly at the grain boundary. The Al and Si possess the functions of refining the grain size. The corrosion resistance can be enhanced by the addition of Si in Zn-Al-Mg alloy coating. ©, 2015, Central South University of Technology. All right reserved.