The Study On The Property Improvement Of ZZNAL4Y Die Casting Zinc Alloy

In the industry application of China, it's found that there exist some problems in the zinc-aluminum alloy (3.5%⁴.3%Al), such as the instability of the comprehensive performance resulting from the high content of the impurity. In order to improve its mechanical properties, to preserve its performance stability and to meet the demands of industry, we studied the microstructure and properties of ZZnAl4Y alloy based on the research status both at home and abroad.In present work,the ZZnAl4Y alloy was chosen as the base alloy. By adding silicon, manganese, boron and rare earth elements to the alloy, the properties of the alloy was optimized. The alloy was melted by means of the medium frequency induction furnace and graphite crucible electric resistance furnace. The tensile strength, hardness and impact ductility of the alloy were tested with the help of electronic universal testing machines, R-150 Rockwell hardness tester and HXD1000T microhardness tester, impact tester. The microstructure of the alloy was observed by optical microscope, scanning electron microscopy and electron probe microanalysis. By analyzing the microstructure and mechanical properties of the alloy, the optimal element content was determined and high performance die casting zinc alloy was obtained. The experimented results show that:(1) The solubilities of silicon, manganese in zinc are very small. The element Mn mainly exists in the form of manganese-rich compounds which appear hard and brittle. The element Si exits mainly in the form of monocrystalline silicon. Either silicon or manganese has the metamorphism to zinc alloy. They can refine the based alloy and increase the contents of eutectic structure. Adding element Si or Mn into ZZnAl4Y alloy can greatly improve its tensile strength and hardness, but the ductility and impact toughness decrease. When adding 0.06⁰.1wt.% Si and 0.05⁰.1wt.% Mn, ZZnAl4Y has high comprehensive mechanical properties.(2) Adding element B into the zinc alloy results the formation of Al-B compounds. These compounds can be used as an effective heterogeneous nucleation of theηphase. So the primaryηphase could be refined. When adding 0.05wt. % B, the zinc alloy has perfect comprehensive properties. (3) After adding element Ti into the zinc alloy, the Al-Ti compounds (TiAl₃, TiAl₂, etc.), Zn-Ti compounds (Zn₁6Ti, Zn₈Ti, etc.) and ternary compounds will be formed. Those compounds will be beneficial to the nucleation ofηphase, which results in the refining of the grain of the matrix. With the increasing of Ti content, the tensile strength and elongation of the zinc alloy increase at first and then decrease. The hardness of the alloy decreases at first and then increases. The impact toughness decreases a little. When the content of Ti is 0.04wt.% ⁰.05wt.%, the zinc alloy has better comprehensive mechanical property. (4) The solubilities of the RE in zinc and aluminum are very small. RE in the alloy will react with zinc, aluminum and some other elements, so a series of complex compounds (such as LaZn₁3, LaZn₈, LaB₉, LaB₆, LaB₄) will be formed. These compounds can improve the nucleation rate of the matrix andηand refine the zinc alloy. All of these are beneficial to the improvement of comprehensive performance of the alloy.