高強7000系鋁合金中析出相協(xié)助的有效晶粒細(xì)化及其成形性
發(fā)布時間：2018-08-11 10:16
【摘要】：高強7000(Al-Zn-Mg-Cu)系鋁合金可作為替代汽車鋼結(jié)構(gòu)件的潛在材料使用,但其受成形性與耐蝕性方面的限制而無法在汽車領(lǐng)域獲得廣泛應(yīng)用。目前7000系鋁合金成形性方面的研究主要集中在成形工藝的改進(jìn)上而忽略了材料本身組織和性能的影響。晶粒細(xì)化能提高5000(Al-Mg)、6000(Al-Mg-Si)系鋁合金及BH烘烤硬化鋼等汽車材料的成形性,7000系鋁合金成形性的改善必然也會受益于晶粒細(xì)化。晶粒細(xì)化可通過中間形變熱處理工藝實現(xiàn),其主要利用大尺寸MgZn2相在再結(jié)晶過程中的粒子誘導(dǎo)形核作用實現(xiàn)組織細(xì)化。本文利用形變誘導(dǎo)析出和粒子誘導(dǎo)形核機(jī)制研發(fā)了兩套短流程的晶粒細(xì)化工藝,使高強7000系鋁合金的塑性和成形性獲得極大提高,并為其在汽車結(jié)構(gòu)件上的應(yīng)用提供了組織和工藝調(diào)控原理。 研究發(fā)現(xiàn),與過時效相比,溫/冷變形都明顯加速固溶態(tài)7075和7050鋁合金中MgZn2相的時效動力學(xué),短時內(nèi)可獲得大量0.5-0.6μm均勻分布的MgZn2粒子,該粒子的析出受熱力學(xué)和動力學(xué)兩方面因素控制。基于此提出的兩套晶粒細(xì)化工藝(W-TMT和C-TMT)均能顯著縮短板材制造時間(從RI-ITMT工藝所需的8h縮短至1h內(nèi)),且在總變形量相同或相近時,兩套工藝均可獲得與RI-ITMT工藝相似的細(xì)晶組織。 分析了不同參數(shù)對最終再結(jié)晶晶粒尺寸的影響并深入研究了再結(jié)晶機(jī)理。研究發(fā)現(xiàn)Mg,Zn2尺寸越大、初始晶粒尺寸越小、變形儲能越大、固溶再結(jié)晶升溫速率越快均能明顯促使形成細(xì)晶組織,而固溶保溫時間對晶粒尺寸影響較小。400℃/6s和480℃C/2s退火可使W-TMT軋板完全再結(jié)晶,且再結(jié)晶速度遠(yuǎn)高于大尺寸MgZn2的回溶速度,因此Mg,Zn2能很好的發(fā)揮粒子誘導(dǎo)形核作用：大尺寸MgZn2粒子強烈增加再結(jié)晶形核點數(shù)量,降低再結(jié)晶溫度,縮短再結(jié)晶時間。而且,大尺寸MgZn2的引入可促使再結(jié)晶困難的7050鋁合金很容易實現(xiàn)完全再結(jié)晶和組織細(xì)化,避免了無限增大變形儲能或延長固溶再結(jié)晶時間的常規(guī)處理手段。 W-TMT工藝所獲細(xì)晶7075鋁合金T6態(tài)的抗拉/屈服強度與RI-ITMT細(xì)晶及傳統(tǒng)熱軋(HR)粗晶樣品基本一致,而延伸率明顯高于HR粗晶樣品,細(xì)晶樣品性能各向異性也明顯改善,表明組織細(xì)化在保證高強度的同時可顯著提高7075鋁合金的延伸率并消除強度、塑性各向異性。同樣,W-TMT和C-TMT加工的細(xì)晶7050鋁合金在保證高強度的同時可實現(xiàn)20%以上的延伸率,遠(yuǎn)高于文獻(xiàn)報道值。晶粒尺寸對7000系鋁合金的強度影響微弱,但卻顯著影響其延伸率,其中晶粒尺寸為～9μm時所表現(xiàn)出來的最高加工硬化能力確保了此時7075和7050鋁合金可獲得最高延伸率 W-TMT-7075細(xì)晶樣品的杯突值與RI-ITMT細(xì)晶樣品相當(dāng),W-TMT細(xì)晶樣品200℃時杯突值(10.7mm)遠(yuǎn)高于HR粗晶樣品200℃杯突值(8.5mm)。晶粒尺寸是影響成形性的關(guān)鍵因素,其對成形性和延伸率的影響規(guī)律一致,且晶粒尺寸為～9μm時的成形性最好。同時,W-TMT-7075鋁合金經(jīng)200℃溫成形+烤漆處理后可獲得類似于回歸再時效處理的組織和性能,因此在細(xì)化7000系鋁合金晶粒的基礎(chǔ)上采用200℃溫成形+烤漆的方法可獲得高強、耐腐蝕的成形樣品,符合汽車結(jié)構(gòu)材料對綜合性能的要求。
[Abstract]:High strength 7000 (Al-Zn-Mg-Cu) aluminum alloy can be used as a potential substitute for automotive steel structural parts, but it can not be widely used in automotive field because of the limitation of formability and corrosion resistance. Grain refinement can improve the formability of 5000 (Al-Mg), 6000 (Al-Mg-Si) aluminum alloy and BH bake hardening steel, and the improvement of 7000 series aluminum alloy formability will inevitably benefit from grain refinement. In this paper, two short-process grain refinement processes have been developed by using the deformation-induced precipitation and particle-induced nucleation mechanisms, which greatly improve the plasticity and formability of 7000 series aluminum alloys and provide the principle of organization and process control for their application in automotive structural parts.
It is found that the aging kinetics of MgZn2 phase in 7075 and 7050 aluminum alloys can be accelerated obviously by warm/cold deformation compared with over-aging. A large number of MgZn2 particles with uniform distribution of 0.5-0.6 micron can be obtained in a short time. The precipitation of the particles is controlled by thermodynamics and kinetics. Two sets of grain refinement processes (W-TMT and C-TM) are proposed. T) can significantly shorten the manufacturing time of sheet metal (from 8 h to 1 h required by RI-ITMT process), and the fine grains similar to RI-ITMT process can be obtained by both processes at the same or similar total deformation.
The effect of different parameters on the final recrystallization grain size was analyzed and the recrystallization mechanism was studied. It was found that the larger the size of Mg and Zn2, the smaller the initial grain size, the larger the deformation energy storage, and the faster the rate of heating up of solid solution recrystallization, the more obvious fine grain structure was formed, while the effect of solid solution holding time on grain size was less. C/2s annealing at 480 C and 480 C can completely recrystallize the W-TMT rolled sheet, and the recrystallization rate is much higher than that of large size MgZn2. Therefore, Mg and Zn2 can play a very good role in particle-induced nucleation: large size MgZn2 particles increase the number of recrystallization nucleation points, reduce the recrystallization temperature and shorten the recrystallization time. The 7050 aluminum alloy with difficulty in recrystallization can easily achieve complete recrystallization and microstructure refinement, avoiding the conventional treatment of infinitely increasing deformation energy storage or prolonging solid solution recrystallization time.
The tensile/yield strength of T6 state of fine grain 7075 aluminum alloy obtained by W-TMT process is basically the same as that of RI-ITMT fine grain and traditional hot-rolled (HR) coarse grain samples. The elongation of T6 state is obviously higher than that of HR coarse grain samples. The anisotropy of fine grain samples is also obviously improved. The results show that the elongation of 7075 aluminum alloy can be significantly increased and eliminated while the high strength is ensured. Similarly, the fine grained 7050 aluminum alloy processed by W-TMT and C-TMT can achieve more than 20% elongation while maintaining high strength, which is much higher than the reported value. Grain size has a weak influence on the strength of 7000 series aluminum alloy, but has a significant effect on its elongation, and the grain size is the highest when the grain size is between 9 micron. The work hardening ability ensures that the maximum elongation of 7075 and 7050 aluminum alloy is obtained at this time.
The cupping value of W-TMT-7075 fine-grained sample is similar to that of RI-ITMT fine-grained sample. The cupping value (10.7 mm) of W-TMT fine-grained sample is much higher than that of HR coarse-grained sample at 200 C (8.5 mm). Grain size is the key factor affecting formability, and its effect on formability and elongation is the same. The formability of W-TMT fine-grained sample with grain size of 9 um is the best. The microstructure and properties of W-TMT-7075 aluminum alloy can be obtained by warm forming at 200 C and baking varnish treatment, which is similar to that of regression re-aging treatment. Therefore, the high strength and corrosion-resistant forming samples can be obtained by warm forming at 200 C and baking varnish on the basis of refining 7000 series aluminum alloy grains, which meets the requirements of automotive structural materials for comprehensive properties.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG146.21
本文編號：2176703
[Abstract]:High strength 7000 (Al-Zn-Mg-Cu) aluminum alloy can be used as a potential substitute for automotive steel structural parts, but it can not be widely used in automotive field because of the limitation of formability and corrosion resistance. Grain refinement can improve the formability of 5000 (Al-Mg), 6000 (Al-Mg-Si) aluminum alloy and BH bake hardening steel, and the improvement of 7000 series aluminum alloy formability will inevitably benefit from grain refinement. In this paper, two short-process grain refinement processes have been developed by using the deformation-induced precipitation and particle-induced nucleation mechanisms, which greatly improve the plasticity and formability of 7000 series aluminum alloys and provide the principle of organization and process control for their application in automotive structural parts.
It is found that the aging kinetics of MgZn2 phase in 7075 and 7050 aluminum alloys can be accelerated obviously by warm/cold deformation compared with over-aging. A large number of MgZn2 particles with uniform distribution of 0.5-0.6 micron can be obtained in a short time. The precipitation of the particles is controlled by thermodynamics and kinetics. Two sets of grain refinement processes (W-TMT and C-TM) are proposed. T) can significantly shorten the manufacturing time of sheet metal (from 8 h to 1 h required by RI-ITMT process), and the fine grains similar to RI-ITMT process can be obtained by both processes at the same or similar total deformation.
The effect of different parameters on the final recrystallization grain size was analyzed and the recrystallization mechanism was studied. It was found that the larger the size of Mg and Zn2, the smaller the initial grain size, the larger the deformation energy storage, and the faster the rate of heating up of solid solution recrystallization, the more obvious fine grain structure was formed, while the effect of solid solution holding time on grain size was less. C/2s annealing at 480 C and 480 C can completely recrystallize the W-TMT rolled sheet, and the recrystallization rate is much higher than that of large size MgZn2. Therefore, Mg and Zn2 can play a very good role in particle-induced nucleation: large size MgZn2 particles increase the number of recrystallization nucleation points, reduce the recrystallization temperature and shorten the recrystallization time. The 7050 aluminum alloy with difficulty in recrystallization can easily achieve complete recrystallization and microstructure refinement, avoiding the conventional treatment of infinitely increasing deformation energy storage or prolonging solid solution recrystallization time.
The tensile/yield strength of T6 state of fine grain 7075 aluminum alloy obtained by W-TMT process is basically the same as that of RI-ITMT fine grain and traditional hot-rolled (HR) coarse grain samples. The elongation of T6 state is obviously higher than that of HR coarse grain samples. The anisotropy of fine grain samples is also obviously improved. The results show that the elongation of 7075 aluminum alloy can be significantly increased and eliminated while the high strength is ensured. Similarly, the fine grained 7050 aluminum alloy processed by W-TMT and C-TMT can achieve more than 20% elongation while maintaining high strength, which is much higher than the reported value. Grain size has a weak influence on the strength of 7000 series aluminum alloy, but has a significant effect on its elongation, and the grain size is the highest when the grain size is between 9 micron. The work hardening ability ensures that the maximum elongation of 7075 and 7050 aluminum alloy is obtained at this time.
The cupping value of W-TMT-7075 fine-grained sample is similar to that of RI-ITMT fine-grained sample. The cupping value (10.7 mm) of W-TMT fine-grained sample is much higher than that of HR coarse-grained sample at 200 C (8.5 mm). Grain size is the key factor affecting formability, and its effect on formability and elongation is the same. The formability of W-TMT fine-grained sample with grain size of 9 um is the best. The microstructure and properties of W-TMT-7075 aluminum alloy can be obtained by warm forming at 200 C and baking varnish treatment, which is similar to that of regression re-aging treatment. Therefore, the high strength and corrosion-resistant forming samples can be obtained by warm forming at 200 C and baking varnish on the basis of refining 7000 series aluminum alloy grains, which meets the requirements of automotive structural materials for comprehensive properties.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG146.21
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