| ZZnAl4Y die casting zinc alloy has been widely used in industrial production and people's life due to its excellent casting properties and stable mechanical properties.However,there are many problems in the use of the zinc alloy,such as poor comprehensive mechanical properties and dimensional instability.In order to further improve the microstructure and mechanical properties of the alloy and meet the requirements of industrial production and use,the melting and casting process of ZZnAl4Y die casting zinc alloy was improved.Si and La elements were used to micro alloyed the alloy.Al content was optimized and the alloy was stabilized.The microstructure and comprehensive mechanical properties of ZZnAl4Y die casting zinc alloy were studied by means of optical microscope,SEM / EDS,pendulum impact tester and electronic universal tensile tester.The results are as follows.(1)When the melt of zinc alloy is solidified in the metal mold at room temperature,the uniformity of initial ?-Zn phase is very poor.With the increase of metal mold temperature,the microstructure uniformity of ZZnAl4Y die casting zinc alloy increases continuously.When the metal mold temperature is 300?,the roundness of primary ?-Zn phase is the best and the microstructure uniformity of the alloy is the best.Compared with that of ZZnAl4Y zinc alloy without melt quench,the microstructural uniformity of the quenched melt of ZZnAl4Y die casting zinc alloy increases obviously after the melt is solidified in the room temperature metal mold.With the increase of metal mold temperature,the roundness and uniformity of the primay ?-Zn phase in the quenched zinc alloy are increasing.When the temperature of metal mold is 300?,the roundness and uniformity of primay ?-Zn phase are the best.Compared with that of ZZnAl4Y alloy obtained by casting the non quenched melt at room temperature metal mold,the tensile strength and elongation as well as impact work of ZZnAl4Y alloy obtained by casting the quenched melt at300 ? metal mold increase 33.9%,320% and 21.7% respectively.Besides,the alloy shows the characteristics of ductile fracture.(2)Si exists in the form of Si particles in the ZZnAl4Y die casting zinc alloy.Si can eliminate the primary phase dendrite and refine the microstructure.When the Si content is 0.3%,the microstructure refinement effect is the best,and the zinc alloy has the best comprehensive mechanical properties.Compared with ZZnAl4Y die casting zinc alloy,the tensile strength and elongation as well as impact work of Si alloying zinc alloy are increased by 17.6%,8% and 6.5%respectively.La exists as La Zn compound in the ZZnAl4Y die casting zinc alloy containing 0.3%Si.La breaks the ?-Zn dendrite into quasi equiaxed grains.When the La content is 0.05%,the microstructure refinement and uniformity effect of ZZnAl4Y alloy is the best.When the La content is 0.05%,the ZZnAl4Y die casting alloy has the best comprehensive mechanical properties,and the tensile strength and elongation as well as impact work of the alloy are increased by 12.2%,31%and 16% respectively.(3)With the increase of Al content,the proportion of primary ?-Zn phase in the structure gradually decreases until disappears,and the morphology of primary ?-Zn phase changes from coarse dendrite to plum and globular.When the Al content is 4.1%,the primar ?-Zn phase in zinc alloy is distributed uniformly in the eutectic structure with smaller plum shaped or spherical grains,and the comprehensive mechanical properties of the alloy are the best.After annealing,the larger dendrites in the microstructure of ZZnAl4Y die casting zinc alloy are broken into plum or spherical crystals.When the annealing time is 4h,the microstructure uniformity and comprehensive mechanical properties of ZZnAl4Y die casting zinc alloy are the best.Compared with the ZnAl4Y alloy without annealing,the tensile strength and elongation as well as impact work of the alloy after annealing at 150?for 4 hours at are increased by 17.1%,91.7% and 23.4% respectively. |
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