Effects Of High Mechanical Pressure On The Solidification Of The ZA27 Alloy

Feeding characteristic is very weak in Zn-Al alloy solidified under common pressure. It tends to form casting shrinkage, porosities which greatly reduce the mechanical properies of alloy and restrict the applications of the alloy. There needs to be an effective process method to improve the solidification of ZA27 alloy. In this thesis, based on understanding of high pressure material science, the samples of Zn-Al alloys were prepared under high pressure, the solidified characteristics of the ZA27 were investigated.The crystal structure of ZA27 alloy changes obviously under high mechanical pressure. Under 3GPa pressure, the crystal spacing of Al-richαphase in the (200), (220) and (311) crystal faces reduces 1.07% , 1.15% and 1.43%, respectively the lattice index of Al-rich phase is 4.048 at common pressure and reduces to 4.00468 at 3GPa pressure. At the same time, the relative change of Al-richαphase crystal spacing in the (200),(220) and (311) crystal faces is also measured.The microstucture of ZA27 alloy has obvious change under high pressure. From common pressure to 5GPa pressure, the microstucture of ZA27 alloy changes from thick dendrites, fine dendrites, granular, vermiform and finally to thick dendrites. At common pressure, the phases of ZA27 alloy are made up of Al-richαphase,Zn-richβphase and e (CuZn₅) phase, this results show that the divorce eutectic arises at 4 GPa pressure, there are siganificant changes on phase composition of ZA27 alloy at 5GPa.γ(AlCu₄) phase which grows lamellarly nucleates and growes attached to theαphase. At the same time, structure of AM arises under high pressure. Aging treatment (150℃×1h) of ZA27 alloy has not metastable phase from common pressure to 5GPa pressure.With the pressure increased, elements of alloy distribute homogeneously. Up to 5GPa pressure, the distribution of elements are very homogeneous, there is few of segregation of elements.