Effects Of High Pressure And Cooling Rate On The Solidiifed Microstructures And Mechanical Properties Of Zn-Al Alloy

In this thesis, ribbon and cylindrical samples with a diameter of5mm respectivelywere prepared by melt spinning and copper mould casting, Zn-22%Al alloy were preparedby rapid compression. Solidified microstructures and mechanical properties of the Zn-Alalloys in the different pressure and cooling rates were investigated.Zn-22%Al alloys under common pressure and high pressure are composed of α and ηphases. The solidified microstructures of the alloys change with the increase of pressure.The microstructures change from vermiform to fine latticework and microhardness ofalloys increases.The Zn-Al alloys under different cooling rates are composed of α and η phases. Thevolume fraction α phase of ribbon Zn-5.1%Al increases obviously and the solidifiedmicrostructures of Zn-Al alloys change obviously with the change of cooling rate. Themicrostructure of Zn-5.1%Al master alloy shows random, and the microstructure of thecylindrical sample shows chrysanthemum-like and fine dendrite patterns. Themicrostructure of Zn-22%Al and Zn-27%Al master alloys shows vermiform, and themicrostructure of the cylindrical experiences a process of fine dendrite patterns.Comparing with Zn-68.4%Al master alloy, the grain size of cylindrical alloy decreases.The microstructure of the ribbon samples shows isometric crystals, the grain size is smallerthan that of other samples. With cooling rate increasing, the microhardness of Zn-5.1%Alalloys increases obviously, but the change of microhardness of Zn-22%Al, Zn-27%Al andZn-68.4%Al alloys are not obvious and the microhardness of Zn-68.4%Al ribbon alloysdecreases obviously. Under the condition of rapid solidification, atomic diffusion isrestrained and forming the supersaturated solid solution. The interplanar spacing and lattice parameter of α phase is remarkably bigger than that of other samples solidified at a lowercooling rates.