摘要
本文以AZ91D镁合金及ZM6稀土镁合金为基体,M40石墨纤维为增强体,采用压力浸渗技术分别制备出结构为单向板(纤维60vol.%)和层合板(纤维50vol.%,铺层角度为±23°)的石墨纤维增强镁基复合材料。
利用金相显微镜、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、电子拉伸试验机和热分析仪研究了碳纤维增强镁基复合材料的微观组织、力学性能和热膨胀性能,探讨了基体类型、热处理工艺、增强体排布方式等因素对复合材料性能的影响,纤维排布设计,使复合材料在二维平面内满足近似各向同性。
研究结果表明,复合材料组织致密,纤维与基体结合良好。M40/AZ91D和M40/ZM6复合材料界面处分别存在Al17Mg12和Mg12Nd两种不同析出相。经过退火及T6处理,Cf/Mg复合材料界面处析出物数量增加,尺寸增大,导致复合材料力学性能下降。随着铺层纤维角度的增加,单向Cf/Mg复合材料抗弯强度及弹性模量逐渐降低,材料失效由纤维断裂拔出过渡为界面开裂,复合材料各向异性明显。±23°层合板结构复合材料可有效缓解单向板复合材料力学性能各向异性。
Cf/Mg复合材料热膨胀系数同样受到热处理方式的影响,铸态、退火态及T6态复合材料线膨胀系数依次降低。单向Cf/Mg复合材料热膨胀系数具有明显的方向性,随着测试方向与纤维取向夹角从0°到90°增加,M40/AZ91D热膨胀系数从1.4~19.4×10~(-6)/K递增, M40/ZM6的热膨胀系数变化范围为1.2~18.4×10~(-6)/K。采用Kelly模型可以准确计算单向复合材料的热膨胀系数。20℃~150℃范围内,±23°M40/AZ91D层合结构复合材料的平均线膨胀系数变化范围小于单向板变化范围,明显改善单向板的各向异性。根据Kelly模型,预测出的±23°M40/AZ91D层合板复合材料的热膨胀系数与测试值符合良好。基于此模型对Cf/Mg复合材料纤维排布进行设计,结果表明,当复合材料采用±45°纤维排布时,其热膨胀系数在平面内近似各向同性,此时M40/AZ91D层合板复合材料热膨胀系数值约为3.82×10~(-6)/K。
With the AZ91D and RE-ZM6 magnesium alloys as matrix and the M40 graphite fibers as reinforcement, carbon fiber-reinforced magnesium matrix composites, including unidirectional fiber(60vol.%fiber) and laminates(50vol.% fiber,±23°of ply orientation), were fabricated by the pressure infiltration technique.
The microstructure, mechanical property and thermal expansion property of M40/AZ91D and M40/ZM6 composites were studied by employing optical microscope, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electronic tensile test machine and dilatometer. And the effects of many factors such as the matrix type, heat treatment process, arrangement sequences of reinforcement on the properties of composites were investigated.
The result shows that the composites are dense and well-bonded. Two kinds of precipitates, Al17Mg12 and Mg12Nd, are found at the interface of M40/AZ91D and M40/ZM6 composites, respectively. After the heat treatment, the amounts of precipitates are increased in the Cf/Mg composites interface, and the sizes are enlarged. These result in decreased of the bend strengths of composites. As the increasing of the fiber orientation angle the bend strength and elastic modulus of unidirectional Cf/ Mg composites are reduced. The failure modes transit from fiber pulling-out to interface de-bonding. The composite materials show obvious anisotropy. The composite laminates with±23°of the fiber arrangement has better mechanical properties and can effectively alleviate the anisotropic properties of unidirectional composites.
The coefficient of thermal expansion (CTEs) of Cf / Mg composites is also affected by heat treatment. The CTEs of composites are decreased in an order of casting, annealing and T6 treatment. The CTEs of unidirectional Cf/ Mg composites are obviously anisotropic. Increased CTEs are found as fiber orientation rises. The CTEs of M40/AZ91D are in the range of 1.4~19.4×10~(-6)/K, while the CTEs of M40/ZM6 lie in the range of 1.2~18.4×10~(-6)/K. The Kelly model can be used to accurately calculate the CTEs of the unidirectional composites. Within the scope of 20℃~ 150℃, the variation of average linear CTEs of±23°M40/AZ91D composite laminates is less than that of unidirectional composites, resulting in an obvious improvement in anisotropy. According to Kelly model, the CTEs of±23°M40/AZ91D composite laminates are predicted. The calculation results show that when the fiber arrangement angle in the laminate is closed to 45°, the composite materials exhibit approximate isotropic property, with a CTE of about 3.82×10~(-6)/K for the M40/AZ91D composite laminates.
引文
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