本文選題：超高強鋁合金 + 變形特性��； 參考：《中北大學》2016年博士論文

【摘要】：超高強鋁合金具有高的比強度和硬度、耐久且經濟、易于加工、較好的耐腐蝕性能和較高的韌性等優(yōu)點,已成為航空和航天、兵器、交通運輸?shù)刃袠I(yè)首選結構材料之一。以自主研發(fā)的超高強鋁合金(Al-12Zn-2.4Mg-1.2Cu-0.3Zr-0.05 Ni)為研究對象,通過熱模擬試驗展開合金的熱變形特性研究;在開展不同工藝參數(shù)對合金力學性能影響的基礎上,以某型號用心部雙凸盤形零件作為應用目標構件,針對其高服役性能和性能均一性要求,結合合金自身應力敏感性特點,提出了狀態(tài)參量(?'和?)和過程參量(W??)作為均勻性評價指標,開展成形方案設計及成形均勻性研究;采用灰色關聯(lián)理論與正交試驗法相結合的優(yōu)化設計方法,借助于數(shù)值仿真技術,開展了目標構件均勻成形工藝參數(shù)優(yōu)化設計研究;最后,進行了成形試驗和構件性能均一性研究。通過熱模擬試驗,開展了合金熱變形特性研究;通過構建熱加工圖,獲得了不同真應變下的最佳變形工藝參數(shù)窗口;在經典Arrhenius模型的基礎上,采用應變補償和應變速率敏感指數(shù)修正相結合的方法,構建了綜合考慮應變補償和應變速率指數(shù)修正的模型。與經典模型相比,預測精度提高了24.88%。基于流變曲線和加工硬化率理論,開展了合金動態(tài)再結晶臨界條件研究,構建了合金發(fā)生動態(tài)再結晶臨界應力和應變條件模型。借助于金相檢測技術,開展了不同變形條件下的動態(tài)再結晶微觀組織觀察與表征研究,結果表明:合金的再結晶晶粒平均尺寸隨溫度的升高、應變速率的降低而增大;隨溫度的降低、應變速率的增加而減小。在此基礎上,借助于定量金相分析技術和形態(tài)學圖像處理技術,建立了合金的微觀組織模型,為后續(xù)數(shù)值仿真研究提供材料模型。通過擠壓比試驗,開展了不同工藝參數(shù)下合金力學性能響應研究,結果表明:變形溫度和擠壓比對合金力學性能具有較顯著的影響。與初始擠壓棒材室溫力學性能(抗拉強度700-720MPa)相比,經二次變形后的抗拉強度提高了7.9%-15.6%。針對目標構件高服役性能及均一性要求,結合合金自身應力敏感性特點,從微觀結構和能量狀態(tài)角度,提出了狀態(tài)參量(等效應變面密度均勻因子,?)、(等效應力面密度均勻因子,?')和過程參量(等效耗散功增量面密度均勻因子,?W?)作為成形均勻性評價指標。并依據狀態(tài)參量,進行了目標構件成形方案設計,制定出多道次等溫成形方案。首次采用了灰色關聯(lián)度與正交試驗法相結合的工藝參數(shù)優(yōu)化設計方法,通過連續(xù)工序下多個變形參數(shù)、應力和應變狀態(tài)結果以及能量分布狀態(tài)結果的灰色關聯(lián)度分析,實現(xiàn)了多評價指標的關聯(lián)集成,解決了正交試驗法無法開展多評價指標下成形工藝參數(shù)優(yōu)化設計難題。在此基礎上,獲得多道次等溫成形工藝參數(shù)組合和連續(xù)工序下不同因素對成形均勻性影響的顯著關系。最后,進行了目標構件的成形試驗和微觀組織與性能測試表征研究。結果表明:所制定的多道次等溫成形(case2)工藝方案合理可行。case2方案成形構件的室溫抗拉強度均值大于730MPa,伸長率均值大于5%;較單道次成形(case1)方案分別提高了5.3%和2.3%。case2方案成形構件的力學性能在要求取樣的方向上無顯著差異(P-value=0.168806),有效保障了成形構件力學性能一致性;且微觀組織中再結晶體積分數(shù)更高,平均晶粒尺寸更加細小,有效保障了成形構件微觀組織的均勻性。case1方案成形構件的抗拉強度在要求取樣的方向存在顯著差異(P-value=0.780749)。采用case2方案和優(yōu)化設計后的工藝參數(shù)制備出了力學性能一致性較好的構件,為該合金在目標構件均勻成形及工程化應用奠定了基礎。
[Abstract]:Ultra high strength aluminum alloy has the advantages of high specific strength and hardness, durable and economical, easy to process, good corrosion resistance and high toughness. It has become one of the preferred structural materials in aviation and aerospace, weapons, transportation and other industries. The research object is Al-12Zn-2.4Mg-1.2Cu-0.3Zr-0.05 Ni, which is developed independently. On the basis of the influence of different technological parameters on the mechanical properties of the alloy, the double convex disc parts of a certain type of heart were used as the target component, and the state parameters (? ') were put forward on the basis of the characteristics of the high service performance and uniformity of the alloy and the stress sensitivity characteristics of the alloy. And?) and process parameters (W?) as the index of uniformity evaluation, the design of forming scheme and the study of forming uniformity are carried out. The optimization design method which combines the grey relation theory with the orthogonal test method and the numerical simulation technology is used to carry out the optimization design of the uniform forming process parameters of the target component. Finally, the forming test and the forming test are carried out. The thermal deformation characteristics of the alloy were studied by the thermal simulation test. Through the construction of the thermal processing diagram, the optimum parameters window of the deformation process under different true strain was obtained. On the basis of the classic Arrhenius model, the combination of strain compensation and strain rate sensitivity index correction was used to construct a comprehensive test. In comparison with the classical model, the prediction accuracy of the model is improved by 24.88%. based on the rheological curve and the theory of machining hardening rate. The critical conditions for dynamic recrystallization of the alloy are studied, and the critical stress and strain condition model of the alloy's dynamic recrystallization is constructed. The microstructure observation and characterization of dynamic recrystallization under different deformation conditions show that the average size of recrystallized grain increases with the increase of temperature and strain rate, and decreases with the increase of temperature and strain rate. On this basis, the quantitative metallographic analysis and morphological image processing are used. The microstructure model of the alloy was established, and the material model was provided for the subsequent numerical simulation. The mechanical properties of the alloy under the different process parameters were studied by the extrusion ratio test. The results showed that the deformation temperature and extrusion ratio had a significant influence on the mechanical properties of the alloy. Compared with the tensile strength 700-720MPa, the tensile strength after two times of deformation increases the high service performance and homogeneity of the target member by 7.9%-15.6%.. According to the characteristics of the stress sensitivity of the alloy, the state parameters (equivalent strain surface density uniformity factor,?) are proposed from the micro structure and energy state. The process parameters (the equivalent of the equivalent dissipative energy increment surface density factor, W?) are used as the evaluation index of the forming uniformity. The forming scheme of the target component is designed according to the state parameters, and the multi-channel isothermal forming scheme is formulated. The method of optimizing the process parameters combining the grey correlation with the orthogonal test method is first adopted. The grey correlation analysis of multiple deformation parameters, stress and strain state results and energy distribution state results in the continuous process has realized the association integration of multi evaluation index, and solved the problem of optimization design for forming process parameters under the multi evaluation index of orthogonal test. On this basis, the multi pass isothermal forming process was obtained. The significant relationship between the parameters combination and the influence of different factors on the forming uniformity in the continuous process. Finally, the forming test of the target component and the characterization of the microstructure and performance test are carried out. The results show that the multi pass isothermal forming (case2) process is reasonable and feasible, and the mean of the tensile strength of the forming component at room temperature is larger than that of the.Case2 scheme. In 730MPa, the average elongation is greater than 5%, and the mechanical properties of the 5.3% and 2.3%.case2 schemes have no significant difference (P-value=0.168806) in the direction of sampling, which can effectively guarantee the mechanical properties of the forming components, and the volume fraction of the recrystallization in the microstructures is higher, and the average grain size is higher. The size is more small and the microstructure uniformity of the forming component is effectively guaranteed. The tensile strength of the.Case1 forming component is significantly different in the direction of the required sampling (P-value=0.780749). The components with good mechanical properties are prepared by using the case2 scheme and the optimized design parameters, which is the alloy in the target component. The foundation of the homogenization and engineering application is laid.

【學位授予單位】：中北大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG146.21
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本文編號：1894325