【摘要】：隨著航空航天工業(yè)向輕量化發(fā)展,帶有縱橫內(nèi)筋結(jié)構(gòu)的H型截面鋁合金鍛件得到廣泛的應(yīng)用。這類構(gòu)件由于承載大部分載荷且所處工作環(huán)境極為惡劣,被要求具有較高的尺寸精度、較好的組織流線分布及優(yōu)良的綜合力學(xué)性能。因此,對(duì)這類鋁合金構(gòu)件的成形工藝、熱處理工藝及后期淬火殘余應(yīng)力消除工藝的研究對(duì)提高該類合金鍛件的性能至關(guān)重要。論文采用熱模擬實(shí)驗(yàn)、熱模鍛生產(chǎn)試驗(yàn)、常溫力學(xué)拉伸、斷裂韌性實(shí)驗(yàn)、顯微組織觀察(OM、SEM)、殘余應(yīng)力檢測(cè)實(shí)驗(yàn)、冷壓實(shí)驗(yàn)及有限元數(shù)值模擬,研究了7050鋁合金H型截面鍛件熱模鍛成形工藝,研究了固溶溫度、淬火介質(zhì)以及淬火轉(zhuǎn)移時(shí)間對(duì)7050鋁合金試件中第二相粒子、晶粒結(jié)構(gòu)、材料強(qiáng)度及斷裂韌性的影響,研究了7050鋁合金構(gòu)件在不同淬火工藝下的殘余應(yīng)力大小、分布及規(guī)律,研究了不同模壓工藝對(duì)7050鋁合金構(gòu)件淬火殘余應(yīng)力的影響。相關(guān)結(jié)論如下:(1)采用Gleeble試驗(yàn)機(jī)對(duì)7050鋁合金在溫度300-450℃,應(yīng)變速率為0.01-10s-1條件下對(duì)7050鋁合金進(jìn)行熱壓縮試驗(yàn),得到了合金不同變形情況下的真實(shí)應(yīng)力-應(yīng)變曲線。對(duì)熱壓縮實(shí)驗(yàn)數(shù)據(jù)進(jìn)行回歸分析,基于雙曲正弦Arrhenius方程,建立了用Z參數(shù)表示的7050鋁合金本構(gòu)關(guān)系。該本構(gòu)模型為后期的數(shù)值模擬分析奠定理論基礎(chǔ)。(2)基于響應(yīng)面優(yōu)化算法,對(duì)7050鋁合金H型截面鍛件熱模鍛成形工藝參數(shù)進(jìn)行優(yōu)化,將優(yōu)化后的工藝參數(shù)應(yīng)用到實(shí)際生產(chǎn),獲得成形質(zhì)量完好的模鍛件。通過(guò)對(duì)鍛件熱模鍛成形中出現(xiàn)的充填不滿、流線穿流、變形不均勻等缺陷問(wèn)題的形成機(jī)理進(jìn)行分析,結(jié)合數(shù)值模擬與響應(yīng)面法(RSM),對(duì)熱模鍛成形工藝參數(shù)進(jìn)行優(yōu)化,得到鍛件成形最優(yōu)工藝參數(shù)。(3)研究和揭示了不同固溶溫度對(duì)7050鋁合金組織和性能的影響。7050鋁合金熱處理過(guò)程中大部分的第二相粒子會(huì)隨著固溶處理的進(jìn)行逐漸的融入到基體中去,隨著固溶溫度的升高,第二相粒子逐漸減少而后趨于穩(wěn)定。然而隨著固溶溫度的升高,晶粒發(fā)生再結(jié)晶的比例也會(huì)增大。因此,隨著固溶溫度升高,合金的強(qiáng)度以及斷裂韌性先升高后降低,在固溶溫度為470°C時(shí)達(dá)到峰值,此時(shí)合金的抗拉強(qiáng)度(σb)、屈服強(qiáng)度(σ0.2)以及斷裂韌性(KIC)分別為567MPa、512MPa和37.2MPa·m1/2。(4)研究和揭示了不同淬火介質(zhì)、淬火轉(zhuǎn)移時(shí)間對(duì)7050鋁合金組織和性能的影響。不同淬火介質(zhì)、淬火轉(zhuǎn)移時(shí)間對(duì)7050鋁合金淬火過(guò)后第二相粒子體積分?jǐn)?shù)有較為明顯的影響,但對(duì)淬火過(guò)后的組織形態(tài)影響不大。四種淬火介質(zhì)中鹽浴淬火工藝下的淬火過(guò)后的鋁合金中的第二相粒子體積分?jǐn)?shù)最小,因而其時(shí)效過(guò)后的力學(xué)性能最好。其次是淬火介質(zhì)為水時(shí)及淬火介質(zhì)為20%PAG溶劑;空冷狀態(tài)下的淬火過(guò)后的鋁合金中的第二相粒子體積分?jǐn)?shù)最大,因而其時(shí)效過(guò)后的力學(xué)性能最差。另外,水淬工藝下,隨著淬火轉(zhuǎn)移時(shí)間的增加,淬火過(guò)后合金中第二相粒子逐漸增多,時(shí)效后合金的力學(xué)性能逐漸下降。(5)研究和揭示了不同淬火介質(zhì)、淬火轉(zhuǎn)移時(shí)間對(duì)7050鋁合金H型截面鍛件淬火后殘余應(yīng)力的影響。鍛件淬火后表層殘余應(yīng)力為拉應(yīng)力,芯部為壓應(yīng)力。鍛件淬火殘余應(yīng)力主要集中在過(guò)渡圓角區(qū)域,其隨著鍛件筋板的厚度增加而增大。另外,鍛件表面淬火殘余應(yīng)力隨著過(guò)渡圓角的增大而增大;芯部淬火殘余應(yīng)力隨著過(guò)渡圓角的增大反而減小。四種淬火介質(zhì)當(dāng)中,淬火介質(zhì)為空氣時(shí)鍛件淬火殘余應(yīng)力值最小,其次是20%PAG溶劑,水及NaCl溶液下的鍛件淬火殘余應(yīng)力相對(duì)較高。隨著淬火轉(zhuǎn)移時(shí)間的增大,鍛件截面過(guò)渡圓角區(qū)淬火殘余應(yīng)力值逐漸減小。(6)研究了不同冷壓工藝對(duì)7050鋁合金H型截面鍛件淬火殘余應(yīng)力的影響。通過(guò)數(shù)值模擬確定先筋頂圓角同時(shí)下壓,下壓結(jié)束后再對(duì)鍛件腹板部分進(jìn)行冷壓是最佳的冷壓工藝。優(yōu)化后的模具使得鍛件整個(gè)截面淬火殘余應(yīng)力得到有效的控制,鍛件殘余應(yīng)力消減到40 Mpa以下。隨著模壓量的增大,鍛件截面過(guò)渡圓角區(qū)殘余應(yīng)力先減小后增大,在模壓量為3%時(shí)達(dá)到最低值。模壓后的試件表面殘余應(yīng)力實(shí)驗(yàn)結(jié)果與數(shù)值模擬結(jié)果比較吻合,實(shí)驗(yàn)測(cè)試值與數(shù)值模擬值誤差在30MPa以內(nèi),說(shuō)明采用數(shù)值模擬的方法測(cè)試試件淬火殘余應(yīng)力有著較高的精度。
[Abstract]:With the development of aerospace industry toward lightweight, H-shaped aluminum alloy forgings with longitudinal and transverse internal ribs have been widely used. These components are required to have high dimensional accuracy, better microstructure and streamline distribution, and excellent comprehensive mechanical properties because they bear most of the loads and work in very bad environment. The forming process, heat treatment process and Post-Quenching residual stress relief process of quasi-aluminium alloy components are very important to improve the properties of such alloy forgings.Thermal simulation test, hot die forging production test, mechanical tensile test at room temperature, fracture toughness test, microstructure observation (OM, SEM), residual stress detection test and cold pressing test are used in this paper. The hot die forging process of 7050 aluminum alloy H-section forgings was studied by means of finite element numerical simulation. The effects of solution temperature, quenching medium and quenching transfer time on the second phase particles, grain structure, material strength and fracture toughness in 7050 aluminum alloy specimens were studied. The residual stress of 7050 aluminum alloy components under different quenching conditions was also studied. The influence of different molding process on the residual stress of 7050 aluminum alloy was studied. The conclusions are as follows: (1) The hot compression test of 7050 aluminum alloy was carried out by Gleeble testing machine under the conditions of temperature 300-450 C and strain rate 0.01-10s-1, and the true deformation of 7050 aluminum alloy was obtained. The constitutive relation of 7050 aluminum alloy expressed by Z parameter is established based on the hyperbolic sinusoidal Arrhenius equation. The constitutive model lays a theoretical foundation for the later numerical simulation analysis. (2) Based on the response surface optimization algorithm, the hot die forging worker of 7050 aluminum alloy H-section forging is studied. The process parameters were optimized, and the optimized process parameters were applied to the actual production to obtain the forgings with good forming quality. The forming mechanism of defects such as filling dissatisfaction, streamline crossflow and uneven deformation in hot die forging was analyzed, and the forming process of hot die forging was studied by numerical simulation and response surface methodology (RSM). (3) The effects of different solution temperatures on the microstructure and properties of 7050 aluminum alloy were studied and revealed. Most of the second-phase particles will be gradually incorporated into the matrix with the solution treatment, and the second-phase particles will increase with the solution temperature. As the solution temperature increases, the strength and fracture toughness of the alloy increase first and then decrease, reaching a peak value at 470 C, at which time the tensile strength (_b), yield strength (_0.2) and fracture toughness of the alloy reach a peak value. The effects of quenching transfer time on the microstructure and properties of 7050 aluminum alloy with different quenchants were studied and revealed. The effect of quenching transfer time on the volume fraction of the second phase particles after quenching in different quenchants was obvious, but the morphology of the second phase particles after quenching was affected. The volume fraction of the second phase particles in the aluminum alloy quenched by salt bath quenching in four kinds of quenching media is the smallest, so the mechanical properties after aging are the best. In addition, with the increase of quenching transfer time, the second phase particles in the alloy increase gradually after quenching, and the mechanical properties of the alloy decrease gradually after aging. (5) The effect of quenching transfer time on the mechanical properties of 7050 aluminum alloy H-section forgings quenched by different quenchants was studied and revealed. The residual stress in the surface layer of the forging is tensile stress and that in the core is compressive stress. Among the four quenchants, the value of quenching residual stress in air is the smallest, followed by 20% PAG. The value of quenching residual stress in water and NaCl solution is relatively high. The influence of different cold-pressing processes on the quenching residual stress of 7050 aluminum alloy H-section forgings was studied.The numerical simulation showed that the best cold-pressing process was to press the fillet of the top of the rib at the same time and then cold-pressing the web part of the forgings after the end of the cold-pressing.The optimized die could effectively control the quenching residual stress of the whole section of the forgings and the forgings. The residual stress decreases below 40 Mpa. With the increase of die pressure, the residual stress in the transition fillet of the forging section decreases first and then increases, reaching the lowest value when the die pressure is 3%. The numerical simulation method is used to test the quenching residual stress of specimens with high accuracy.
【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG319;TG156.3

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