本文選題：Al-Zn-Mg-Cu系鋁合金 + RE�。� 參考：《沈陽工業(yè)大學》2017年碩士論文

【摘要】：Al-Zn-Mg-Cu系鋁合金具有高強度、高韌性、良好的機械加工性和焊接性、耐腐蝕和抗低周疲勞等優(yōu)良的綜合性能,在航空航天、工業(yè)和民用等領域具有極其廣泛的應用,挖掘該合金的潛力仍然是當前鋁合金研究方面的重點。微合金化是提高Al-Zn-Mg-Cu系鋁合金綜合性能的重要手段之一。目前研究開發(fā)出的多種微合金化元素中,以稀土元素Sc對Al-Zn-Mg-Cu系鋁合金的性能改善最為顯著。本課題在含Sc的Al-Zn-Mg-Cu系鋁合金基礎上添加不同含量的稀土元素Ce,并對合金的組織、時效析出行為、硬度、拉伸和低周疲勞行為進行研究,以期為研制出優(yōu)良綜合性能的超高強鋁合金提供理論依據(jù)。顯微組織觀察結(jié)果表明:添加0.2%的Ce,可以顯著消除鑄態(tài)Al-7.5Zn-2Mg-2.3Cu-0.1Sc合金的粗大樹枝晶,有效地細化合金的鑄態(tài)顯微組織,并使合金擠壓態(tài)和T6態(tài)組織晶粒更加均勻細小。硬度和拉伸試驗結(jié)果表明:在120°C×32 h的人工時效過程中,Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的硬度、強度呈先增加后降低的趨勢。合金中添加0.2%的Ce的可顯著地提高Al-7.5Zn-2Mg-2.3Cu-0.1Sc合金的布氏硬度、抗拉強度和屈服強度。拉伸斷口分析結(jié)果表明峰時效階段,Al-7.5Zn-2Mg-2.3Cu-0.1Sc-0.2Ce合金和的拉伸斷口表面可觀察到大量韌窩和少量沿晶斷裂,表現(xiàn)為以韌性為主的混合斷裂特征。Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的強化機制主要為η'相的時效析出強化,添加0.2%的Ce可以使η'相析出更加均勻彌散,并使晶界無析出帶變窄。低周疲勞實驗結(jié)果表明,在應變幅控制的低周疲勞加載條件下,T6態(tài)Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金均表現(xiàn)出循環(huán)穩(wěn)定現(xiàn)象;加入0.2%的Ce可以提高合金疲勞變形抗力的同時提高合金低周疲勞壽命。T6態(tài)Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金的載荷反向周次與塑性應變幅、彈性應變幅之間均呈線性關(guān)系并分別服從Coffin-Manson和Basquin公式。疲勞斷口觀察結(jié)果表明,在低周疲勞加載條件下,T6態(tài)Al-7.5Zn-2Mg-2.3Cu-0.1Sc-xCe合金中的疲勞裂紋均在疲勞試樣表面萌生,并且以穿晶方式進行擴展。
[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 擄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.
【學位授予單位】：沈陽工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.21

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