Papers by Keyword: Zinc Aluminium Alloy

Abstract: Under high pressure of more than 1GPa, the grain growing process of Zinc-Aluminium (ZA) alloy is difficult observed by experimental method, therefore numerical simulation method is used to observe grain growing process of ZA alloy. Pressure as a important variable is leading-in thermodynamic parameters of ZA alloy, then solute diffusion and redistribution model, grain nucleating and growing model are present, and dendrite growth module is applied to describe grain growth. The simulation results of grain growth process under high pressure are demonstrated: In the initially solidification stage, grains are equiaxed growing process, after 15s solidification time, dendrite arm size are not equal, the reason is there are nonhomogeneous temperature fields around grains, which make some grains appear fast growing velocity, even it can be observed that dendrite arm of different grains are meet each other at 25s solidification time. Comparing simulated microstructure with experimental microstructure under 2GPa high pressure, it shows both grain size and grain distribution are similar, proving that the grain growing process can be well observed by simulation method.

Abstract: The processing of metals through the application of severe plastic deformation provides the potential for achieving exceptional grain refinement in bulk solids. Several SPD methods are now available but processing by high-pressure torsion (HPT) has attracted much attention over the last five years. Numerous reports are now available describing the application of HPT to a range of pure metals and simple alloys and excellent grain refinement were achieved using this process with the average grain size often reduced to the nanoscale range. However, in order to make this technique more practical, the nature of the sample characteristics immediately after conventional HPT must be considered in order to understand the fundamental principles of HPT processing. This report examines the procedure with special emphasis on the evolution in hardness homogeneity in both high-purity aluminum and a Zn-22% Al eutectoid alloy processed by HPT.

Abstract: In this study, some low-titanium aluminum alloys produced by electrolysis were prepared and the effect of various titanium contents on microstructure and tensile property of Zn-Al alloy was investigated. The test results showed that addition of titanium by electrolysis is an effective way to refine the grain size of Zn-Al alloy. As the titanium content is 0.04 wt%, the grain size becomes to be a minimum value and the tensile property of the alloy reaches to the maximum. Electrolysis showed that titanium atoms are to be some inherent particles in low-titanium aluminum alloy. These titanium atoms enter into the aluminum melt liquid and spread to the whole melt rapidly under stirring action of electromagnetic field of the electric current. The heterogeneous phase nuclei are high melting TiC and TiAl3 particles formed from in-situ precipitating trace C and Ti during cooling process. These in-situ precipitating heterogeneous nucleation sites with small dimension, high dispersity, cleaning interface and fine soakage with melt, have better capacity of heterogeneous nucleation than of exotic particles. It may inhibit grain growth faster and more effective in pinning dislocations, grain boundaries or sub-boundaries.

Abstract: The atoms site preference in the Al₃Ti-Zn system has been studied using H. Rietveld method. The L12 Ti(Al, Zn)₃ particles evolve in a ZnAl25 melt from the L1₂TiZn₃ particles in the ZnTi4 master alloy. It is found that Zn is replaced by Al during the transformation TiZn₃ → Ti(Al, Zn)₃. In the evolving fcc L12 Ti(Al, Zn)₃ phase Ti occupies (0, 0, 0) position while Al and Zn occupy (0, 0.5, 0.5) position, similarly to Al and X in the Al₃Ti-X systems, where X = Ni, Cr, Mn, Cu, Ag, Pd [1, 2].

Abstract: The microstructure of cast Zn-25wt%Al alloy inoculated by addition of a Zn-4wt%Ti master alloy (ZnTi4) has been studied using scanning electron microscopy and electron back-scatter diffraction (EBSD). It is found that Ti(Al,Zn)₃ particles act as nucleation centres for grains of the primary solid solution of Zn in Al (α' phase). The Ti(Al,Zn)₃ particles evolve in melt from the TiZn₃ particles in the ZnTi4 master alloy. EBSD shows that α' phase dendrites are in the same crystallographic orientation as the Ti(Al,Zn)₃ particles on which they nucleate. It is also found that some of the Ti(Al,Zn)₃ particles do not have any well-defined crystallographic orientation relationship with the α' phase. These particles were probably pushed and then engulfed by growing α' grains which had already nucleated on other particles.

Abstract: ZA27 alloy solidifies in the way of paste-solidification, and results in gravity segregation. The two-phase flow model was developed on the basis of the solidification characteristic of the ZA 27 alloy. And the governing equations of the solidification process were differentiated and computed in a 3-D cylindrical coordinate system through a heat and fluid simulation software package (PHOENICS). The computation of the concentration field indicated a segregation of Al, and is in good agreement with the experiments. This model could simulate the convection and the gravitational segregation during the solidification.