【作者】 特日昆；

【导师】 王浩伟；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2012， 硕士

【摘要】 轻质、高强、高模量原位自生铝基复合材料管材在航空航天、国防工业等领域具有广泛的应用前景。本文研究课题的主要目的是通过反挤压工艺制造出高强度,高模量的铝基复合材料管材。为了得到高模量,选用高体积分数的TiB₂增强颗粒,由于高体积分数的增强颗粒在基体材料中存在流动性差,界面结合不好等问题,所以选取流动性好的铸造共晶铝合金作为基体材料。但铸造铝基复合材料的塑形较差,因此采用反挤压的方法来改善其塑形,并得到复合材料管材。本文采用热模拟与实际试验相结合的方法,对复合材料的高温热加工行为进行研究。内容包括:探讨材料的高温流变行为,确定温度和应变速率等对于材料热变形的影响,建立了材料的热变形本构方程。应用动态材料模型建立材料的热加工图,确定热加工合适的加工工艺。最后对材料进行反挤压试验来验证热加工图的分析结果,并对不同处理状态下的材料进行性能比较及相关分析。本文首先通过Gleeble3500热模拟机研究TiB₂/Al-Si-Mg-Cu铝基复合材料的高温流变行为,实验结果表明TiB₂/Al-Si-Mg-Cu铝基复合材料在高温热变形时存在稳态流变特征,随着流变应力应变速率的增大而增大,随着温度的升高而降低,同时根据热模拟得到的真应力—真应变曲线计算得出了复合材料的热变形本构方程。根据热模拟实验得到的数据,绘制了TiB₂/Al-Si-Mg-Cu铝基复合材料的功率耗散图和热加工图。功率耗散图结果表明:随着温度的升高和应变速率的降低,功率耗散率增大,有利于材料的动态再结晶;从材料的热加工图上可以看出,该复合材料在实验范围内有两个失稳区域,一个是低温高应变速率区域,该区域的失稳主要由于基体裂纹的产生和颗粒的脱粘断裂引起的,另一个区域是高温中等应变速率区域,造成材料的失稳的主要原因可能是楔形开裂和颗粒的脱粘断裂,在加工时应当尽量避免这两个区域。在高温低应变速率区域,如500℃,10-3 s^-1的实验条件下,功率耗散率最高且与稳定区相对应,是TiB₂/Al-Si-Mg-Cu铝基复合材料的最佳加工区域。根据热加工图上得到的加工工艺,对TiB₂/Al-Si-Mg-Cu复合材料实体材料进行反挤压实验后,发现在温度为500℃,应变速率为10-3 s^-1的实验条件下,材料表面光滑,没有微裂纹,的确为材料的最佳加工区域。而在300℃,1 s^-1的实验条件下,材料表面发生宏观开裂。最后对不同处理条件下的TiB₂/Al-Si-Mg-Cu复合材料进行力学性能测试。显微硬度的测试结果为:未经过处理的原始复合材料<反挤压后的复合材料<反挤压后经过T6热处理的复合材料。又对TiB₂/Al-Si-Mg-Cu复合材料进行反挤压变形,测试其拉伸性能。可以发现经过反挤压后,复合材料的抗拉强度,弹性模量和延伸率均有大幅度提高,分别提高了53.8%,16.9%和191.4%。对经过反挤压和未经过反挤压的材料均进行T6热处理,可以发现对于无论是否经过反挤压的复合材料,热处理过后抗拉强度有很大提高,弹性模量变化不大,而延伸率有所降低。其中力学性能最好的为反挤压后经过热处理的TiB₂/Al-Si-Mg-Cu复合材料。更多还原

【Abstract】 Light weight, high strength and high modulus in situ aluminum composite pipe have a broad prospect of application in aerospace, national defense industry fields. The main purpose of the paper is to produce high strength and high modulus of aluminum composite pipes through backward extrusion. In order to get high modulus, we choose large volume fraction TiB₂ particle reinforcement. Large volume fraction particle reinforcement have bad flow ability and interfacial bonding, so we choose casting eutectic aluminum composite as matrix material which have good flow ability. However, casting aluminum composites have bad plasticity. We choose the method of backward extrusion to improve plasticity and gain the composite pipes.This paper combines the thermal simulation and actual experiments to research flow stress behaviors of composite materials at high temperature. The contents include: discussing flow stress behaviors of composites at high temperature and how temperature and strain rate influence flow stress behaviors; establishing the thermal deformation constitutive equation of composites; drawing power dissipation maps and processing maps according to dynamic material model; doing backward extrusion experiments to prove results of processing maps and making performance comparisons of composites under different conditions and related analysis.Firstly, the paper studied flow stress behaviors of TiB₂/Al-Si-Mg-Cu composite at high temperature using Gleeble3500. The results showed that TiB₂/Al-Si-Mg-Cu composite has steady-state flow characteristics during hot deformation. The flow stress increased with the strain rate and decreased with the temperature. Meanwhile, the paper figured out the constitutive equation according to the true stress—true strain curves of composites.According to the data of hot simulation, the paper draws the power dissipation maps and processing maps. The power dissipation maps showed that power dissipation efficiencies of TiB₂/Al-Si-Mg-Cu composite increased with temperature and decreased with strain rate. That was helpful to dynamic recrystallization. From the processing maps, it would be found there were two instable regions. One was the region with high strain rate and low temperature which was mainly due to matrix crack and particle debonding and crack. The other was the region with high temperature and middle strain rate which could be due to wedge crack and particle debonding and crack. The two regions should be avoided in the hot deformation. The optimum working region was the region with high temperature and low strain rate, for example, 500℃,10-3 s^-1. The region was stable and the power dissipation efficiency was highest. According to the processing map, it was found that 500℃,10-3 s^-1 was the optimum working region after backward extrusion. The composite had smooth surface and no cracks. But under the condition of 300℃,1 s^-1, there were macro cracks in the surface.At last, the paper tested the performances of composites under different conditions. The result of microstructure hardness showed: original composite < composite after backward extrusion < composite after backward extrusion and T6 heat treatment. The results of tensile tests showed that after extrusion, the tensile strength, modulus and elongation increased very much, by 53.8%, 16.9% and 191.4% separately. Whether the composite was heat treated, it could be found that the tensile strength increased, the modulus had no change and the elongation decreased. The best composite was the one after backward extrusion and heat treatment.更多还原