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Study of the Phosphides in Al-X (Si,Zr,Ca)-P Alloys

Author: ZuoMin
Tutor: LiuXiangFa
School: Shandong University
Course: Materials Processing Engineering
Keywords: Al-Si alloy Phosphide Crystal growth Cluster structure Heterogeneous nucleation
CLC: TG115
Type: PhD thesis
Year: 2010
Downloads: 69
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Abstract

In this paper, high-powered video microscope (HSVM), electron probe micro-analyzer (EPMA), X-ray diffraction instrument (XRD), differential scanning calorimetry instrument (DSC), transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM) and other tests were studied by means of Al-Si-P, Al-Zr-P, Al-Si-Ca-P alloy phosphide. Al-Si-P melt AlP clusters structure and growth mechanism proposed the AlP twins concave angle; invented a highly efficient and stable master alloy of Al-Zr-P reveals ZrP, AlP between the evolution behavior ; the clear inhibition mechanism of Ca, Al-Si-Ca-P alloy AlP; Al-Si-P master alloy of Al-Zr-P refinement of hypereutectic Al-Si alloy behavior. The research work of this paper are as follows: AlP cluster structure in (1) Al-Si-P melt growth mechanism using first-principles molecular dynamics simulation of AlP clusters Al80Si15P5 melt structure, further explained AlP the evolution of behaviors in the Al-Si melt. The study found that the P-atom is present around a strong chemical short programs at 1100 ℃ the melt P atom as the core Al6P structural unit, and the melt temperature was raised to 2600 ℃ when the structural changes (6Al Si) P. The study found that the Al-Si-P-based alloy phase composed of three objects, namely, the α-Al, Si and ALP. Thermodynamic analysis shows that AlP crystal {111} crystal plane growth pattern for the growth of a small plane, {100}, {110} crystal faces are non-facet growth. Al-Si-P alloy fracture analysis, observed AlP twins edges and grooves. On this basis the the AlP twins concave angle growth mechanism, in order to explain the growth process of the AlP in Al-Si melts, that AlP from higher concentrations of elements groove at the twins began to grow, continue with the crystal growth, some high-index planes disappear, eventually AlP crystal is close-packed {111} planes surrounded. (2) Al-Zr-P alloy ZrP evolution and growth mechanism study by first-principles molecular dynamics simulations found in Al90Zr5P5 alloy system, Zr-P interaction forces between the atoms is much larger than the other various The force between the atoms, i.e., Zr atom is inclined at a first nearest neighbor and more P atoms bonded. In, Al90Zr5P5 alloy melt temperature of 800 ° C (6Al Zr) P structural unit. Under a temperature of 1600 ℃, Al90Zr5P5 alloy melt (7Al Zr) P structural unit. The study found that, Zr, introduced to the Al-P alloy melt under the smelting conditions wherein the ALP can be converted into ZrP excluding AlP Al-Zr-P alloy which can be prepared by α-Al ZrAl3 and ZrP. Further studies showed that adding Si to Al-Zr-P alloy, ZrP evolved into AlP. In this alloy system, ZrP the duplex face-centered cubic structure phase after extraction and processing to render the cube structure. Further, in the ZrP the crystal growth process, the growth rate differences between the various crystal faces will lead to the formation of different morphologies. Meanwhile, due to the diffusion effect by the melt, Zr, P atom easier enrichment corners precipitated ZrP particles, thereby promoting the projecting growth of the crystal (111) direction, while the central portion of the {100} crystal PowerPhone easy to form Al enrichment. , ZrP phase showing a cube morphology, while the {100} crystal appear before a funnel-shaped, this structure nucleation phase ZrAl3, growth provides a ready-made stairs. (3) Al-Si-Ca-P alloy Ca elements AlP phase inhibition of Ca as a common impurity elements, a serious impact on the refining effect of phosphorus on primary Si in Al-Si alloy. The analysis revealed that the Al-4Ca-2P alloy system elements Ca exists in the form of Al4Ca, and Ca3P2 phase. Which, Ca3P2 render Article flocculent and rough surface, there is more than one crystal face raised. Al-xSi-2Ca-1P alloy system, i.e. the Si content is followed by 6.0%, 12.0%, 18.0%, and the elements Ca mainly in the form of Al2Si2Ca, and Ca3P2 phase exists. Through the cross-sectional structure of Al-12Si-0.4Ca-0.2P alloy analysis, both calcium-rich phase showed a thick plate-like. Containing Ca about 400ppm Al-12Si alloy to add 200ppmP processing, not presented phosphorus alloy modification effect. The reason is that the Ca and P generated between stable Ca3P2 compound, so that the melt not be used as the primary crystal Si heterojunction core ALP phase. The excess elements Ca prompted alloy showed Na modification effect at the same time, can also be generated with Al, Si reaction the bulky board the sheet Al2Si2Ca phase. (4) Al-Si-P and Al-Zr-P master alloys in eutectic Al-Si alloy AlP clusters, Al-Si-P alloy structure dissolution and precipitation behavior analysis AlP in Al-Si melt behavior refinement process is as follows: large-size particles → dissolving → Al6P the structural unit formed clusters → AlP microcrystalline. For the middle of different phosphorus-containing alloy, and its refinement mechanism are the beginning of AlP heterogeneous nucleation crystal Si, while AlP in the melt needs to experience the above process, before showing a good refining effect. It was found that the Al-17Si-2.5P master alloy microstructure its refinement behavior have a certain impact. For example, the rapid solidification processed Al-17Si-2.5P master alloy AlP relative small size, evenly distributed, which promote the dissolution of AlP refinement process, thus further increasing the P absorption rate, and ultimately improve the refinement efficiency . By orthogonal test optimization of the Al-17Si-2.5P master alloy A390 alloy refinement process, the amount of phosphorus Add 375ppm, melt processing temperature of 800 ° C, holding time 30min. Optimization program, the average size of the primary Si crystals can be by from 116.3μm refinement to 14.0gm render its morphology nearly spherical, the distribution becomes more uniform. Brinell hardness, room temperature tensile strength were increased by 14.1% and 27.8%. Al-6Zr-2P master alloy A390 alloy has good refinement effect. Refinement mechanisms into ZrP in the dual role of heterogeneous atoms of the strong force between Si-Zr and chemical kinetics factors the AlP phase, which play the role of primary Si phase refinement. The master alloy ZrP in the evolution of the Al-Si melt can be expressed as: the the ZrP particles → → dissolved local restructuring → Al6P structural unit formed clusters → AlP microcrystalline.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Analytical tests of the metal (Metal Testing and Materials )
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