Papers by Author: Chun Xiang Xu

Abstract: The Explicit Finite Difference (EFD) method is used for calculating the energy conservation equation during solidification. In order to improve the computational efficiency, the equivalent specific heat method is adopted to calculate the latent heat and the high order Alternating Direction Implicit (ADI) method is also applied, which is fourth order in space and second order in time. The degree of similarity between the simulation results and experimental results is analyzed quantitatively by the Hamming Distance (HD) for the first time, and results show that this high order mathematical model based on the equivalent specific heat method and the high order ADI method is faster and more accurate than the EFD method.

Abstract: Al-Ti-C grain refiners have been prepared by combining self-propagating high-temperature synthesis (SHS) technique and melting-casting method. Effects of Al powder size and C/Ti ratio on the microstructures and grain-refining efficiency of Al-Ti-C grain refiners were studied by OM, XRD, SEM and EDS. The results show that when Al powder size is fine, and C/Ti ratio is 1: 8, SHS reaction among the mixed powders can easily carry on in the melt. As a result, the prepared grain refiner consists of blocky Al3Ti and fine TiC particles distributed in Al matrix, and exhibits excellent grain refining performance on commercially pure Al.

Abstract: To improve the strength-toughness and heat-resistance of die cast magnesium alloy, the ZA85 alloy has been prepared by adding proper amount of spherical quasicrystals containing master alloy. The results indicate that the solidification microstructure is inlaid with quasicrystal particles, which is a new phase i(Mg45Zn47Y5Mn3), co-existing with the α-Mg, Φ(Al2Mg5Zn2) phase and τ(Mg32(AlZn)49) phase. Mechanical properties of ZA85 alloys have been dramatically improved owing to the obvious grain refinement of the matrix microstructure. While adding 1.7 wt % spherical quasicrystal containing master alloy, macro-hardness of ZA85 magnesium alloy reaches 75HB; meanwhile, impact toughness reaches the peak value 18.4Jcm-2, which is about 202% of ZA85 base alloy. Due to the pinning effect of quasicrystal particles on grain boundaries, the strengthened ZA85 alloys would have excellent heat-resistance.

Abstract: Al-Ti-C-P master alloy has been successfully fabricated by SHS-melting technology. Microstructures and phase constituent of Al-Ti-C-P master alloy were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and EDS. The results show that Al-Ti-C-P master alloy comprises TiAl3, TiC, AlP and α-Al matrix. After adding 2.0 wt% Al-Ti-C-P master alloy, microstructure and mechanical properties (after T6 treating) of ZL117 alloy has been improved dramatically: The average grain size of primary silicon decreases from 260 to 35 μm, edges and angles of primary silicon are passivated, the morphology of eutectic silicon changes from large needle-like one to fine rod-like or particle-like one, and the microstructures are noticeably refined; Room temperature tensile strength changes from 168 to 260 MPa while elevated temperature tensile strength (at 300
) varies from 88 to 125 MPa. Impact toughness and macro-hardness(HB) increases to 17 J/cm2 and 97 from the original 6.5 J/cm2 and 92.

Abstract: Effect of Si on the forming ability of quasicrystalline phase in Al65Cu20Fe15 alloys fabricated under conventional casting conditions has been studied using X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM). The results show that under the conventional casting conditions, it is found that the addition of certain amount of Si into the Al-Cu-Fe melts can change the formation of Al62.5Cu25Fe12.5 quasicrystals during the solidification process. Compared with Al65Cu20Fe15 alloy, Al64.5Cu20Fe15Si0.5 alloy has smaller volume fraction of β phase solidifying initially, larger volume fraction of the quasicrystal phase generating in the subsequent peritectic reaction, and larger volume fraction of ω phase solidifying finally. Both experimental results and the theory of Hume-Rothery show that addition of Si can promote the formation ability of the icosahedral quasicrystalline Al62.5Cu25Fe12.5 phase in Al-Cu-Fe alloy.