| Discovery of quasicrystal breaks the conventional definition of crystal but also brings about a revolution in the material field. The in-depth studies and perfection of quasicrystal theory cause positive progress in the field of quasicrystal application. However, quasicrystal can not be directly used as structural materials due to its innate high brittleness. Whereas, some unique properties of quasicrystal, such as high hardness, heat-resistant and low surface energy due to its unusual quasi-periodic lattice structure, which quite favors for its application as a strengthening phase in toughness matrix materials. Zinc based quasicrystal strengthening Zinc alloy provides a new way for application of quasicrystal in industry. Zn-Mg-Ti quasicrystal master alloy, prepared by conventional metal casting method, was added into the ZA27 alloy to improve its wear-resistance and refine its grains. The microstructure evolvement law and phase composition range, in which Zn-Mg-Ti quasicrystal can be formed, has been detailedly discussed by using X-ray diffraction, optical microscope, scanning electron microscope equipped with energy dispersive spectrum. Besides, the growth law as well as morphological characteristics of Zn-Mg-Ti quasicrystal phase and its approximate phase were also investigated. The study on Zinc based quasicrystal strengthening ZA27 alloy is focused on the effect of Zn-Mg-Ti quasicrystal master alloy on the grain refinement and macro-hardness of ZA27 alloy. Results show that:(1) Zn-Mg-Ti quasicrystal phase and its approximate phase were obtained by conventional metal casting method in alloys with composition of Zn67Mg28Ti5. The microstructure of prepared Zn67Mg28Ti5 alloy was indentified as MgZn2 matrix and icosahedral structure by XRD analysis. Results show that Zn-Mg-Ti quasicrystal phase, with stoichiometric composition of Zn71Mg21Ti8, appear to be hexagonal and six-petaled petal-like. Cores of the six-petaled quasicrystal phase and four-petaled approximate phase are hexagonal and quadrilateral. It is indicated that the morphology of phase subsequentially formed is determined by morphology of the core.(2) Atomic ratio of Ti element in Zn-Mg-Ti quasicrystal master prepared by conventional metal casting method should be 5at.%. A new blocky phase with stoichiometric composition of Zn68Mg13Ti19 appears in the solidification when Atomic ratio of Ti exceeds 5at.%. Besides, formation of the blocky phase results in sharp reduction of quasicrystal phase and its approximate phase. With Ti content remains constant,atomic ratios of Zn and corresponding Mg are in the range of 65-70at.% and 30-25at.%, in which Zn-Mg-Ti icosahedral quasicrystal will be formed. The amount of Zn-Mg-Ti icosahedral quasicrystal and its approximate phase reach the maximum when the alloy composition is Zn67Mg28Ti5.(3) The nucleation of Zn-Mg-Ti quasicrystal phase and its approximate phase have to overcome certain nucleating potential barrier in the Zn-Mg-Ti quasicrystal master alloy melt. The power of Zn-Mg-Ti quasicrystal growth after nucleation is derived from phase transformation driving force of Zn-Mg-Ti quasicrystal. The value of phase transformation driving force is depended on the undercooling of surrounding melt. The volume of Zn-Mg-Ti quasicrystal phase and its approximate phase increase with the increasing driving force. The morphologies of Zn-Mg-Ti quasicrystal phase and its approximate phase depend on growth rate in different directions. And the main factor that affects the growth rate is undercooling caused by curvature variation on the interface. The growth rate of sharp corner of Zn-Mg-Ti quasicrystal phase and its approximate phase is fastest, which leads to the petal-like morphology of quasicrystal phase. Growth patterns of Zn-Mg-Ti quasicrystal phase and its approximate phase are laminar growth and its growth interface is smooth interface. Growth behavior of Zn-Mg-Ti quasicrystal phase is similar to that of its approximate phase.(4) The adding temperature should be 600℃by using Zn-Mg-Ti quasicrystal master alloy strengthening ZA27 alloy. This adding temperature could make sure that MgZn2 matrix of Zn-Mg-Ti quasicrystal master alloy dissolve and Zn-Mg-Ti quasicrystal phase can be inherited to ZA27 alloy. Zn-Mg-Ti quasicrystal master alloy addition can increase the nucleation sites for ZA27 alloy and prevent dendrite growth. The microstructure is best refined when Zn-Mg-Ti quasicrystal master alloy addition is 3wt.%. Meanwhile, its hardness reaches the peak value (140HB). This could be attributed to the improvement of local deformation resistance caused by Zn-Mg-Ti quasicrystal. The microstructure of ZA27 alloy begins to coarse and its hardness tends to decrease when Zn-Mg-Ti quasicrystal master alloy addition is more than 3wt.%. This phenomenon can mainly ascribed to the aggregation of quasicrystal phase at the bottom of melt and lose of its strengthening effect.
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