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Research on Fabrication and Processing of In-situ TiB2 Particulates Reinforced 7055 Matrix Composites

Author: XuMeng
Tutor: ChenGang
School: Jiangsu University
Course: Non-ferrous metallurgy
Keywords: 7055 matrix composites Electromagnetic stirring In situ Hot deformation Mechanical properties
CLC: TB331
Type: Master's thesis
Year: 2010
Downloads: 107
Quote: 0
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Abstract


In situ TiB2 particulates reinforeced 7055 composites from 7055Al-K2TiF6-KBF4 system was studied in this paper.Adding minimal Mg and Ce element can promote in-situ reaction greatly;By electromagnetic stirring,ceramics particles are well dispersed and eutectic phases are greatly refined.The comprehensive mechanical properties of materials are improved by hot extrusion,quenching and thermal processing.The solidification microstructure,patterns of in-situ particulate,composition of phase were investigated with the help of optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）,electronic universal testing machine and other modern equipments.The results show that TiB2 particles with radius of 0.4～1μm are synthesized in 7055Al-K2TiF6-KBF4 at 850℃.The morphology of TiB2 are six-rowed granular,parts of them are spheroidized.The grain size of 7055 eutectic phases under electromagnetic stirring are more refined than the grain size of 7055 eutectic phases without influence of electromagnetic stirring.We optimize the grain size and morphology in electromagnetic parameters:current,150A、frequency,4Hz.while,electromagnetic stirring promotes the reaction,the speed of mass and heat conduction.the contact area between high temperature liquid aluminum and mixed salt is expend.the quantity of TiB2 particles is increasing and well dispersed.In the fabrication of in situ TiB2 particles reinforced composites,The results indicate that adding microscale Mg（0.3%） or 3%（wt%） Al-10%Ce can well improve the wettability between ceramic and aluminum melt then promotes the reaction and restrain the TiB2 particles assemble,and also the sizes and morphology of TiB2 are refined largely.The primitive grain boundary of as-deposited material vanished and the reticular phases was disrupted and the grain broke up.The microstructure was more compact and more tiny crowded second-phases precipitated after a series of hot working treatment on cast TiB2/7055 composites:homogenization under 450℃×24h、hot extrusion、quenching process under 480℃×60min、aging under 120℃×24h.Processed after technics above,the tensile strengthσb of 2%（vol%） TiB2/7055 composites achieve 630MPa,which is enhanced than processed under technics conditions obviously,and elongationδis 4.0%.

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