硼酸镁晶须增强镁基复合材料的谱学表征与性能研究

用X射线衍射谱分析了Mg2B2O5w/AZ91D镁基复合材料中的物相。研究了固溶处理和时效处理以及固溶处理加人工时效处理对复合材料组织演变的影响及组织与显微硬度之间的关系。结果表明,经过固溶处理后,共晶相的分解使复合材料的硬度值明显下降。时效处理使得复合材料的硬度逐渐增加并在时效处理16h后出现时效峰值201HV。然而随着时效时间的进一步增加,显微硬度值降低。经固溶处理24h,基体中β相基本溶解,形成过饱和的固溶体,接着时效处理8h,β相以弥散形式析出,从而使得复合材料的显微硬度值提高30%;而固溶处理24h及时效处理24h后,β析出相由细小片状的连续析出相向粗大的层片状非连续析出相过渡,使得复合材料的显微硬度下降到183HV。

Spectroscopic Characterization and Properties of Mg2B2O5w/AZ91D Magnesium Composites

Magnesium borate whisker (Mg2B2O5 w) 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 Mg2B2O5 w/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 degrees C 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 degrees C for 8 and 24 h, respectively, aging treatment at 200 degrees C for 8, 12, 16, 20 and 24 h, respectively and solution at 415 degrees C 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 degrees C for 24 h, the beta-Mg17, Al12 phase is dissolved in the alpha-Mg phase to form oversaturated solid-solution in the composite and then the diffusive beta phase precipitates after subsequent aging treatment at 200 degrees C 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 beta-Mg17 Al12 phase precipitate changed from continuous fine platelets to discontinuous coarse platelets. It was concluded that the process of solution at 415 degrees C for 24 h and subsequent aging treatment at 200 degrees C for 8 h was the best process for the composite.