Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的组织和力学性能
本文选题:Al-Zn-Mg-Cu系铝合金 + RE ; 参考:《沈阳工业大学》2017年硕士论文
【摘要】:Al-Zn-Mg-Cu系铝合金具有高强度、高韧性、良好的机械加工性和焊接性、耐腐蚀和抗低周疲劳等优良的综合性能,在航空航天、工业和民用等领域具有极其广泛的应用,挖掘该合金的潜力仍然是当前铝合金研究方面的重点。微合金化是提高Al-Zn-Mg-Cu系铝合金综合性能的重要手段之一。目前研究开发出的多种微合金化元素中,以稀土元素Sc对Al-Zn-Mg-Cu系铝合金的性能改善最为显著。本课题在含Sc的Al-Zn-Mg-Cu系铝合金基础上添加不同含量的稀土元素Ce,并对合金的组织、时效析出行为、硬度、拉伸和低周疲劳行为进行研究,以期为研制出优良综合性能的超高强铝合金提供理论依据。显微组织观察结果表明:添加0.2%的Ce,可以显著消除铸态Al-7.5Zn-2Mg-2.3Cu-0.1Sc合金的粗大树枝晶,有效地细化合金的铸态显微组织,并使合金挤压态和T6态组织晶粒更加均匀细小。硬度和拉伸试验结果表明:在120°C×32 h的人工时效过程中,Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的硬度、强度呈先增加后降低的趋势。合金中添加0.2%的Ce的可显著地提高Al-7.5Zn-2Mg-2.3Cu-0.1Sc合金的布氏硬度、抗拉强度和屈服强度。拉伸断口分析结果表明峰时效阶段,Al-7.5Zn-2Mg-2.3Cu-0.1Sc-0.2Ce合金和的拉伸断口表面可观察到大量韧窝和少量沿晶断裂,表现为以韧性为主的混合断裂特征。Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的强化机制主要为η'相的时效析出强化,添加0.2%的Ce可以使η'相析出更加均匀弥散,并使晶界无析出带变窄。低周疲劳实验结果表明,在应变幅控制的低周疲劳加载条件下,T6态Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金均表现出循环稳定现象;加入0.2%的Ce可以提高合金疲劳变形抗力的同时提高合金低周疲劳寿命。T6态Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的载荷反向周次与塑性应变幅、弹性应变幅之间均呈线性关系并分别服从Coffin-Manson和Basquin公式。疲劳断口观察结果表明,在低周疲劳加载条件下,T6态Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金中的疲劳裂纹均在疲劳试样表面萌生,并且以穿晶方式进行扩展。
[Abstract]:Al-Zn-Mg-Cu series aluminum alloys have high strength, high toughness, good machinability and weldability, corrosion resistance and low cycle fatigue resistance, and have been widely used in aerospace, industrial and civil fields. Tapping the potential of the alloy is still the focus of the current aluminum alloy research. Microalloying is one of the important methods to improve the comprehensive properties of Al-Zn-Mg-Cu aluminum alloys. Among the various microalloying elements, the rare earth element SC has the most remarkable improvement on the properties of Al-Zn-Mg-Cu aluminum alloy. In this paper, the microstructure, aging precipitation behavior, hardness, tensile and low cycle fatigue behavior of Al-Zn-Mg-Cu aluminum alloy containing SC were studied by adding different content of rare earth element Ce. In order to provide theoretical basis for the development of super-high-strength aluminum alloy with excellent comprehensive properties. The results of microstructure observation show that the coarse dendrite of as-cast Al-7.5Zn-2Mg-2.3Cu-0.1Sc alloy can be significantly eliminated by adding 0.2% ce, and the microstructure of as-cast Al-7.5Zn-2Mg-2.3Cu-0.1Sc alloy can be refined effectively, and the microstructure of the alloy in extruded and T6 state is more uniform and fine. The hardness and tensile test results show that the hardness of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloy increases first and then decreases during artificial aging at 120 掳C 脳 32 h. The addition of 0.2% ce into the alloy can significantly improve the Brinell hardness, tensile strength and yield strength of Al-7.5Zn-2Mg-2.3Cu-0.1Sc alloy. Tensile fracture analysis shows that a large number of dimples and a few intergranular fracture can be observed on the tensile fracture surface of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-0.2Ce alloy during peak aging. The strengthening mechanism of Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloy is mainly the aging precipitation strengthening of 畏 'phase. Adding 0.2% ce can make 畏' phase precipitate more uniformly and narrow the grain boundary without precipitating zone. The results of low cycle fatigue test show that the T6 Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloy exhibits cyclic stability under low cycle fatigue loading condition controlled by strain amplitude. The addition of 0.2% ce can increase the fatigue deformation resistance of the alloy and increase the load reverse cycle and plastic strain amplitude of the low cycle fatigue life of the alloy. The elastic strain amplitude shows a linear relationship and follows the Coffin-Manson and Basquin formulas respectively. The results of fatigue fracture observation show that the fatigue cracks in T6 Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe alloy initiate on the surface of fatigue specimen under low cycle fatigue loading and propagate in transgranular manner.
【学位授予单位】:沈阳工业大学
【学位级别】:硕士
【学位授予年份】:2017
【分类号】:TG146.21
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