The Solidification and Corrosion Behavior Determination of the Ti/B Added Zn-Al-Mg Alloys

Abstract

The solidification and corrosion behavior of the Ti/B added Zn-Al-Mg alloys were experimentally investigated by means of microstructure characterization and electrochemical test. The basic calculations were carried out to predict the characteristics of the Ti-added Zn-Al-Mg alloys. The Zn-Al-Mg ingots with minor doping of Ti/B were prepared and solidified under different cooling rate, including air cooling, water quenching and furnace cooling. The scanning electron microscopy (SEM) and the X-ray diffraction method (XRD) were used to determine the microstructures and phase types of the alloy samples. It could be discovered that trace TiAl₃ particles were dispersed in the Ti/B added alloy samples which provide the heterogeneous nucleation sites to refine the size of the dendrites and the eutectic microstructures. More fined microstructures with the addition of both Ti and B were obtained compared with those with the merely addition of Ti, and the water cooled alloys presented the finest microstructures due to the fastest cooling rate. It could also be noticed that with the increasing solidification rate, the percentage of the MgZn₂ phase turned out to be higher because of the Mg₂Zn₁₁↔MgZn₂ transition, which is in consistent with the results in the actual hot-dip galvanizing process. Electrochemical experiments in the previous work included methods the of the Tafel polarization test and the electrochemical impedance spectroscopy test (EIS). Results show that the quenched Zn-Al-Mg alloy with the addition of both Ti and B takes on best corrosion resistance. Consequently, the addition of certain amount of Ti/B elements and the appropriate elevation of the cooling rate will be the practicable approaches to optimize the microstructure and the corrosion resistance of the Zn-Al-Mg coatings in the actual galvanizing process.

Keywords

Ti/B added Zn-Al-Mg alloy / cooling rate / solidification / corrosion resistance

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