| Abstract:Aiming at the latest development trends in the world on developing high-performance zinc aluminum alloy, we have developed basic research and applied technology research in pressure casting zinc aluminum alloy, gravity casting zinc aluminum alloy and hot-dip zinc aluminum alloy, respectively, for the purpose of offering technological supports for producing high-performance zinc aluminum alloy which can meet the market demands. This study is of great significance in comprehensive utilizing of zinc resource and modernization of industry in our country.The zinc aluminum alloy can meet different users’ demands with strong market competitiveness, as it has low melting point and fusion energy dissipation, good fluidity as well as excellent room-temperature mechanical properties. However, the domestic zinc aluminum alloy have common defects such as low plasticity and toughness, high impurities, low dimension instability as well as low corrosion resistance, so it is of great significance to develop basic research study. The effects of Al on the fluidity, mechanical properties and corrosion resistance of zinc aluminum alloy were studied, the effects of alloying on the microstructure and mechanical properties and the die casting processing of ZnA14die casting alloy were studied, then the effects of hot deformation and heat treatment on microstructure and mechanical properties of ZA27alloy were studied. Moreover, the effects of RE on the corrosion resistance of Zn-5%Al hot dipped zinc aluminum alloy were studied. The major conclusions were drawn as follows.1. The effects of Al on the microstructure, fluidity, mechanical properties and corrosion resistance of Zn-Al alloy were studied, the results show that ZnA14alloy has good fluidity and tensile strength, ZA27alloy has the best tensile strength, Zn-5%Al alloy has good fluidity and corrosion resistance.2. The effects of rare Zr and Sr on the microstructure and mechanical properties of ZnA14alloy were studied, the results show that Zr can effectively refine the η-Zn dendrite and shorten the lamellar spacing. The Al2ZnZr compounds can be formed between the cellular-dendrite structure and pining the grain boundary effectively. Moreover, Zr can trap the impurity of Fe and eliminate the harmful influence of Fe on the properties of ZnA14alloy. When adding0.1%Zr, the alloy has perfect comprehensive properties. Adding element Sr into the alloy results the formation of SrZn13compounds, the primary η-Zn phase is restrained. When adding0.1%Sr, the alloy has perfect comprehensive properties.3. The die casting filling process of ZnA14alloy shell part has been simulated with FLOW-3D software. The die casting processing parameters can be optimized with the help of orthogonal experiment. The simulation results of temperature field, velocity field, pressure field and surface defect concentration show that the optimized processing parameter is pouring temperature420℃, injection speed2.5m/s, mold initial temperature200℃.4. The hot deformation behavior of ZA27alloy was investigated by hot compression tests. One linear regression equation with Z constant has been proposed as the following:Where n=5.21,α=0.007, A=1.81×1010s-1, Q=109.39kJ/mol and Z=εexp(13157/T). A comparative evaluation of the trained ANN model and the constitutive equations has been carried out. It is found that the trained ANN model is more efficient and accurate in predicting the hot deformation behavior of ZA27alloy. Based on the processing map and deformed microstructure, the hot deformation of ZA27alloy can be carried out safely in the region with a strain rate of0.1～1s-1and temperature range of250-350℃.5. The optimal heat treatment conditions of ZA27alloy are as follows:After annealing at360℃for24h, the non-equilibrium βphases at the grain boundaries and the dendritic segregation are eliminated. After solution treatment at365℃for1h, complete dissolution of the solute atoms is obtained. After ageing at140℃for1h, fine uniformly precipitates are obtained, and the Comprehensive mechanical properties are improved significantly.6. The effects of Re on the corrosion behaviors of Zn-5%Al hot dipped zinc aluminum alloys were studied by SEM, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results show that ZnO, Zn5(OH)8Cl2·H2O, Zn5(OH)6(CO3)2and Al2(OH)sCl·2H2O are the main corrosion products of Zn-5%Al-RE coatings. By comparing the corrosion behavior of the Zn-5%Al-RE coatings, the corrosion layer formed on Zn-5%A1-0.6%RE coating is more compact than the other coatings and has the best corrosion resistance. |
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