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Preparation of Al-Mn-Ti Quasi-crystal Master Alloy and Its Application in Al-25%Si Alloy

Author: YangYongJun
Tutor: ZhangJinShan
School: Taiyuan University of Technology
Course: Materials Processing Engineering
Keywords: The middle of the Al-Mn-Ti alloy Al-25% Si alloy Quasicrystals Primary silicon
CLC: TG146.2
Type: Master's thesis
Year: 2010
Downloads: 95
Quote: 1
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Abstract


A long time, the eutectic composition of the Al-Si alloy having a low thermal expansion coefficient, high wear resistance and excellent casting and processing properties, often become the material of choice for small and medium sized combustion engine piston. But with the development of the internal combustion engine to a high-speed, high-power, traditional eutectic composition of Al-Si alloy piston has failed to meet its development needs. So there is a hypereutectic (containing Si = 16 ~ 26wt.%) Al-Si alloy pistons hypereutectic Al-Si alloy with the silicon content increased, the primary silicon becomes very thick, seriously affect the alloy mechanical properties and machinability. Quasicrystals since been found, has been a hot research in materials science community. The quasicrystalline having unique properties, making it particularly suitable as the toughness of the reinforcing base material of high hardness, heat resistance and low surface energy. Quasicrystal reinforced aluminum matrix composites is a research hotspot quasicrystals's important to promote the application and research in this area in the areas to expand the quasicrystalline the application of great significance. This article is based quasicrystal reinforced aluminum matrix composites envisaged, design reference crystal middle of a new type of aluminum alloy, and joined Al-25% Si-Al-Si alloy and hypereutectic Al-Si alloy to improve the organization. The experimental vacuum induction furnace, water-cooled copper mold cooling and solidification, add to the Al-Mn binary quasicrystal alloy Ti element prepared Al-Mn-Ti-based ternary quasicrystalline intermediate alloy. Means of optical microscope, X-ray diffraction (XRD), scanning electron microscopy and energy dispersive analysis, the middle of the quasicrystal of Al-Mn-Ti alloy microstructure and phase composition changes, found a new the petaloid Al67Mn13Ti20 three element quasicrystals, a preliminary study and the process of its formation. At the same time, the middle of the quasicrystal Al-Mn-Ti alloy is added to the Al-25% Si Al - Si alloy in the middle of the quasicrystal Al-Mn-Ti alloy was observed on the morphology of primary silicon. The main findings of this paper are as follows: (1) in the middle of the Al (86-X) Mn14TiX series alloys, quasicrystalline phase formation have not found the presence of the ternary phase material. Since the cooling rate of the alloy in the experiment with the rapid solidification larger gap, without addition of Ti alloy cast structure by α-Al phase and Al6Mn composition; addition of Ti element by the α-Al alloy phase, Al6Mn phase and Al3Ti phase composition, and with the increase in the content of Ti, α-Al phase is gradually reduced, Al3Ti phase is gradually increased. (2) in the series the middle of the quasicrystal alloy of Al (77.5-X) Mn22.5TiX not join Ti there decagonal quasicrystals the presence of the T phase, but can not get the quasicrystals, organizations exist in part of quasicrystals approximate crystal the phase (Al4Mn phase). The addition of Ti element, can refine the quasicrystalline decagonal T-phase grains, and can inhibit the approximate crystal the phase (Al4Mn phase) the formation of the cast structure. When added in an amount of Ti element in 3.5at.%, Was observed in the alloy to the petaloid tissue, through the X-ray diffraction and EDS analysis, to determine its prevail crystal phase, the composition of Al67Mn13Ti20. With the improvement of the Ti content, the increase in the number of petaloid quasicrystalline phase. (3) of Al67Mn13Ti20 quasicrystalline phase formation process analysis, the results showed that: the solidification of the liquid phase is formed first Mn2Ti phase, subsequent peritectic reaction L Mn2 Ti → Al67Mn13Ti20, eventually leading to the ternary Al67Mn13Ti20 quasi-crystal formation. Ternary quasicrystalline phase formed such that the Mn content in the remaining liquid phase to increase and promote the formation of a quasi-crystal of T-phase. The quasicrystal (4) Al67Mn13Ti20 the formation process, follow the nucleation and growth of the law. The quasicrystalline phase growth interface rough interface, based on continuous growth mechanism for growth. As the experiment using a water-cooled copper mold cooling, the cooling rate of the alloy is much larger than the equilibrium solidification, solute atoms formed in the forefront of the growth interface component is too cold so the growth interface increased instability quasicrystalline phase six-like growth, petals end showing the sleek shape. (5) to join Al73.5Mn22.5Ti4 the middle of the quasicrystal alloy Al-25% Si alloy microstructure morphology of significant changes. Primary silicon in the alloy by thick five star to small granular when the middle of the quasicrystal alloy added 4wt.%, The average size of the primary silicon is reduced from 300μm to 30μm, thinning effect is obvious. Meanwhile, with the increase in the amount of the middle of the quasicrystalline alloy is added, the Brinell hardness of the Al-25% Si alloy has improved to some extent.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys
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