In situ reaction TiB_2 particle reinforced 7055 based composites and processing research

Title: In situ reaction TiB_2 particle reinforced 7055 based composites and processing research
　　Author: Xu Meng
　　Degree-granting unit: Jiangsu University
　　Keywords: 7055 matrix composites;; electromagnetic stirring;; situ reaction;; thermal distortion;; mechanical properties
　　Summary:
　　This reaction enhanced by in situ thermal processing of particles and improve the overall performance of 7055 alloy, the system of the 7055Al-K_2TiF_6-KBF_4 system synthesis TiB_2 particle reinforced 7055 matrix composite system, analysis of the composite Magnetic lifter micro-structure; study of trace elements Mg and rare earth elements Ce melt in situ reaction of the catalytic role; and through electromagnetic stirring refinement matrix structure and improve the ceramic particles in Al matrix in the distribution of composite materials using hot extrusion, solution, aging and other processes further improve their mechanical properties.
　　X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electronic universal testing machine and other analytical test methods, analysis of rare earth alloying and in situ particle reinforced 7055 alloy matrix composites 7055 microstructure, phase composition and endogenous particle morphology, size distribution and mechanical properties.
　　The results show that when the reaction temperature is 850 ℃, the aluminum melt K_2TiF_6 + KBF_4 system can generate TiB_2 stable particles. TiB_2 hexagonal particles were significantly shorter column, size between about 0.4 ~ 1μm. 7055 by the electromagnetic stirring processing of alloy grain size than the 7055 does not apply electromagnetic stirring cast alloy was refined. In the electromagnetic stirring current and frequency of 4Hz for the 150A and the material obtained when the smallest grain size; the same time, the electromagnetic stirring to promote the in situ reaction, increasing the temperature of liquid aluminum and the probability of contact between the salt mixture, the reaction interface to expand so TiB_2 increase in the number of particles, the distribution is more diffuse.
　　TiB_2 in situ particle reinforced aluminum composites, the study of trace elements and rare earth elements on the Mg role in promoting the http://www.999magnet.com/products/131-magnetic-lifter in situ reaction. The results showed that: when at 750 ℃, add small amount of Mg (0.3wt%) or 3wt% rare earth alloy Al-10% Ce can improve the well between the ceramic particles and liquid aluminum wettability, and promote the interface reaction, and inhibition TiB_2 segregation of particles, the particles refined.
　　By TiB_2/7055 cast composite homogenization 450 ℃, 480 ℃ solid solution after hot extrusion 60 minutes at 120 ℃ for 24 hours of processing time, the network has been disrupted the second phase, grain crushing, the organization more uniform and compact, and more small dense second phase precipitation. After the above processing of composite materials, tensile strength σ_b to 630MPa, the same process conditions than the 7055 alloy was significantly improved elongation δ is 4.0%.
　　Degree Year: 2010