本文關(guān)鍵詞： 高強(qiáng)度鋁合金 成分 微觀組織 力學(xué)性能 熱力學(xué)　出處：《北京科技大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：我國目前在航空用高強(qiáng)Al-Zn-Mg-Cu系合金(7xxx系鋁合金)的生產(chǎn)、研究方面取得了不少成果,但在成分設(shè)計(jì)、組織控制和強(qiáng)韌化等原理、機(jī)理認(rèn)識(shí)方面仍存不足。成分設(shè)計(jì)對(duì)該系合金強(qiáng)度、韌性和耐蝕性的作用規(guī)律及機(jī)制屬領(lǐng)域核心內(nèi)容,相關(guān)資料國外鮮有公開報(bào)道。系統(tǒng)研究該系合金成分—組織—性能間的關(guān)系對(duì)于理解、消化國外先進(jìn)Al-Zn-Mg-Cu系合金設(shè)計(jì)理念及開發(fā)具有自主知識(shí)產(chǎn)權(quán)的新合金具有重要理論和工程應(yīng)用價(jià)值。本文基于對(duì)該系合金高溫相組成影響更為顯著的Mg、Cu元素含量的調(diào)控,設(shè)計(jì)了系列高Zn含量(約8.5 wt%)的Al-Zn-Mg-Cu合金,研究Mg、Cu元素在制備流程(鑄造、均勻化、軋制、固溶和時(shí)效)中對(duì)組織和主要性能的作用規(guī)律及機(jī)制。此外,采用計(jì)算熱力學(xué)、動(dòng)力學(xué)技術(shù)對(duì)一些重要實(shí)驗(yàn)現(xiàn)象進(jìn)行了模擬分析,實(shí)驗(yàn)與模擬所得規(guī)律基本一致。主要研究結(jié)論如下：設(shè)計(jì)合金的實(shí)際凝固路徑介于Scheil model和Level rule兩種凝固模式之間,且更接近前者。鑄錠中存在的大塊σ相和(σ+θ)團(tuán)塊的含量主要由Mg含量決定,Cu元素的作用次之,具體為：Mg含量越高,形成的大塊。相越多,(σ+0)團(tuán)塊越少；Mg含量相近時(shí),合金Cu含量越高,形成的大塊σ相越多,一般地(σ+θ)團(tuán)塊越多。高M(jìn)g高Cu含量合金難以形成(σ+0)團(tuán)塊。設(shè)計(jì)合金經(jīng)460℃/168 h單級(jí)長(zhǎng)時(shí)和(460℃/24h+475℃/24h)雙級(jí)均勻化處理后的相組成與熱力學(xué)計(jì)算所得Al-Zn-Mg-Cu (Zn=8.5 wt%)四元相圖等溫截面基本相符。研究顯示,460℃平衡相組成受Mg含量影響顯著：低Mg合金更易進(jìn)入Al單相區(qū),即使其含有高的Cu含量。475℃較460℃能更充分溶解第二相,此時(shí)平衡相組成主要由(Mg+Cu)含量決定：(Mg+Cu) 4.35 wt%時(shí)合金可獲得A1單相固溶體,否則難以獲得Al單相固溶體。低Mg含量或高Zn:Mg比有助于加速合金時(shí)效析出進(jìn)程,即合金能更快達(dá)到峰時(shí)效狀態(tài)并具有更大的過時(shí)效速率。這是由于在第一級(jí)時(shí)效120℃/6 h過程中,低Mg含量或高Zn:Mg比能促進(jìn)GPII區(qū)的形成,而高M(jìn)g含量或低Zn:Mg比會(huì)促進(jìn)GPI區(qū)的形成。由于GPI熱穩(wěn)定性較GPII差,高M(jìn)g含量或低Zn:Mg比合金在120℃至160℃升溫過程中較少的GP區(qū)能夠保存下來成為第二級(jí)160℃時(shí)效階段η相的形核點(diǎn)。Cu并不明顯影響時(shí)效進(jìn)程。相同時(shí)效狀態(tài)下,設(shè)計(jì)合金的電導(dǎo)率、硬度、強(qiáng)度和韌性主要由Mg含量決定：提高M(jìn)g含量,合金硬度、強(qiáng)度提高,而電導(dǎo)率、韌性會(huì)相應(yīng)降低。提高Cu含量也能獲得類似效果,但效果較弱。實(shí)驗(yàn)及熱力學(xué)模擬研究表明,提高M(jìn)g含量會(huì)顯著增加欠時(shí)效及過時(shí)效態(tài)合金中析出相粒子的體積分?jǐn)?shù),不明顯影響欠時(shí)效態(tài)合金粒子尺寸,但會(huì)一定程度上減小過時(shí)效態(tài)合金粒子尺寸,進(jìn)而提高欠時(shí)效/過時(shí)效態(tài)合金的強(qiáng)度和硬度。提高合金Cu含量可在一定程度上增大析出相粒子體積分?jǐn)?shù),使合金強(qiáng)度和硬度獲得提高,但其影響明顯弱于Mg。隨Mg含量增加,T76態(tài)合金晶界析出相粒子面積分?jǐn)?shù)增大,晶內(nèi)與晶界無析出區(qū)屈服應(yīng)力差也會(huì)提高,這將促進(jìn)沿晶斷裂,導(dǎo)致合金韌性降低。Cu對(duì)合金韌性的影響較Mg弱。對(duì)于低/中Mg含量(如1.5/2.0 wt%)合金,提高Cu含量會(huì)增大晶內(nèi)與晶界無析出區(qū)屈服應(yīng)力差,并提高合金再結(jié)晶分?jǐn)?shù),這將在一定程度上促進(jìn)沿晶斷裂,導(dǎo)致合金韌性降低。對(duì)于高M(jìn)g含量(如2.5 wt%)合金,提高Cu含量還會(huì)增加固溶處理后粗大未溶金屬間化合物粒子的數(shù)量,進(jìn)而增大合金斷裂傾向,使韌性進(jìn)一步降低。
[Abstract]:China's current use of high-strength Al-Zn-Mg-Cu alloy in aviation (7xxx Aluminum Alloy) production, the research made a lot of achievements, but in the composition design, principle of microstructure control and toughening mechanism, understanding is not enough. The strength of alloy composition design, function mechanism and regularity of toughness and corrosion resistance of the genus the core content areas, foreign related data rarely publicly reported. Study on the alloys component, microstructure and properties of the relationship between the understanding of the new alloy Al-Zn-Mg-Cu alloy digesting foreign advanced design concepts and development with independent intellectual property rights has important theoretical and practical value. The high temperature of the alloy phase composition effect is more remarkable. Based on Mg, Cu control elements, designed a series of high Zn content (about 8.5 wt%) of Mg, Al-Zn-Mg-Cu alloy, Cu element in the preparation process of preparation (casting, homogenization, rolling, solid Effect of solution and aging) law and mechanism of organization and the main performance. In addition, the calculation of thermodynamics, dynamics techniques were simulated and analyzed some important experimental phenomena, experimental and numerical simulation results are basically consistent. The main conclusions are as follows: between the actual design of alloy solidification path between Scheil model and Level rule two solidification mode and, closer to the former. In the presence of large ingot and sigma (sigma + 0) mass content is mainly decided by the content of Mg, effect of Cu elements, in particular: the content of Mg is higher, the formation of bulk phase. More (+0) mass less; similar content of Mg, content of alloy the higher the Cu, the more large the formation of sigma phase, general (+ Sigma Theta) mass. More high Mg alloy with high Cu content (+0) to form clumps. Design of alloy is 460 DEG C /168 h single and prefect (460 DEG /24h+475 DEG /24h) double stage after homogenization treatment phase group With the thermodynamic calculation of income Al-Zn-Mg-Cu (Zn=8.5 wt%) four yuan isothermal section of phase diagram basically. Research shows that 460 C balance phase composition was significantly affected by Mg content: low Mg alloy is more susceptible to Al single-phase regions, even if its containing high content of Cu.475 is 460 DEG C to more fully dissolved in the second phase, the phase equilibrium mainly composed of (Mg+Cu) content: (Mg+Cu) 4.35 wt% alloy can obtain A1 single-phase solid solution, otherwise it is difficult to obtain Al single phase solid solution. The low Mg content or high Zn:Mg ratio helps accelerate the aging process of alloy, the alloy can be quickly reached the peak aging state and has a greater rate of aging. This is because in the first stage of aging at 120 for /6 h, low Mg content or high Zn:Mg ratio can promote the formation of GPII, and high Mg content or low Zn:Mg ratio will promote the formation of GPI area. Due to the thermal stability of GPI was lower than GPII, high or low Zn:Mg ratio and Mg content The gold in the 120 to 160 DEG C during the heating process less GP area to survive to become second 160 ageing stage phase nucleation of.Cu does not significantly affect the aging process. The same aging conditions, conductivity, design of alloy hardness, strength and toughness is mainly determined by the content of Mg, increase the Mg content, the hardness of the alloy that strength is improved, but the electrical conductivity and toughness will decrease. The increase of Cu content can get a similar effect, but the effect is weak. Experimental study and thermodynamic simulation show that increasing the content of Mg significantly increased the volume fraction of precipitates under particle aging and overaging alloy, the influence is not obvious under aged alloy particle size. But to some extent reduce the over aged alloy particle size, thus improving the underaged / overaging alloy strength and hardness of the alloy. Cu can improve the content of a certain increase of precipitates particle volume fraction, the The strength and hardness of alloy is improved, but the effect was weaker than Mg. with the increase of Mg content, the particle phase T76 alloy precipitation area fraction increases, grains and precipitate free zone yield stress difference will increase, which will promote the intergranular fracture toughness of the alloy, lead to reduce the influence of.Cu on the toughness of the alloy is Mg weak. For the low content of Mg (1.5/2.0 / wt%) alloy, increase the content of Cu increases in grain and precipitate free zone yield stress, and improve the recrystallization fraction, this will to some extent promote the intergranular fracture toughness of the alloy, lead to reduced. For the high Mg content (such as 2.5 wt%) alloy, increase the content of Cu will increase the number of solid solution treatment after undissolved intermetallic particles, thereby increasing the alloy fracture tendency, the toughness is further reduced.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG146.21

【參考文獻(xiàn)】

相關(guān)博士學(xué)位論文 前1條

1 王少華;高強(qiáng)鋁合金的微合金化及熱處理工藝研究[D];大連理工大學(xué);2011年

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本文編號(hào)：1524086