Spectroscopic Characterization and Properties of Mg2B2O5w/AZ91D Magnesium Composites
JIN Pei-peng1,2,DING Yu-tian1,XU Guang-ji1, LIU Yan2
1. State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials, Lanzhou University of Technology, Lanzhou 730050, China 2. Institute of Magnesium, Qinghai University, Xining 810016, China
Abstract：Magnesium borate whisker (Mg2B2O5w) reinforced Mg matrix composite was fabricated by vacuum-gas pressure infiltration process. The Mg2B2O5 w preforms forming process was determined. The Mg2B2O5 whiskers were fabricated into a preform by wet forming method without any binder. The Vacuum-Gas Pressure Infiltration process and parameters are also developed. The micrographs revealed reasonably uniform distribution and random orientation of the whiskers in the as-cast Mg2B2O5w/AZ91D composite and the composites were without pores defect. The phases were analyzed by XRD patterns for the as-received whiskers, the whiskers sintered at 1 000 ℃ for 3 h and the as-cast composite, respectively. Then, the microstructure evolution of the composite was investigated when the composite was heat-treated. Meanwhile, the relationships between microstructure and micro- hardness of the alloy heat-treated were also studied. The heat-treatment condition were solution at 415 ℃ for 8 and 24 h, respectively, aging treatment at 200 ℃ for 8, 12, 16, 20 and 24 h, respectively and solution at 415 ℃ for 8 or 24 h and subsequent aging treated for 8, 12, 16, 20, 24 h, respectively. The phases were analyzed by XRD patterns for the composites after different heat treated process. The results of XRD patterns were shown to be in good agreement with the microstructures evolution of the composites. The results showed that the micro-hardness of the solution treated composites is decreased due to resolution of eutectic phase, whereas the micro -hardness of the aged composites was increased gradually and the peak hardness is reached to 201 HV in the composite aged for 16 hours. Solution treatment at 415 ℃ for 24 h, the β-Mg17Al12 phase is dissolved in the α-Mg phase to form oversaturated solid-solution in the composite and then the diffusive β phase precipitates after subsequent aging treatment at 200 ℃ for 8 h; hence the micro-hardness of the composite was increased 30%. However, as the aging time increased to 24 h, the hardness of the composite was reduced to 183 HV because the β-Mg17Al12 phase precipitate changed from continuous fine platelets to discontinuous coarse platelets. It was concluded that the process of solution at 415 ℃ for 24 h and subsequent aging treatment at 200 ℃ for 8 h was the best process for the composite.
Key words：Magnesium based composite;XRD;Heat treatment;Microstructure;Vickers hardness
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