本文選題：2195鋁鋰合金 + 分級時效��； 參考：《哈爾濱工業(yè)大學》2017年碩士論文

【摘要】：為提高航天火箭的有效運載能力,迫切需要實現(xiàn)火箭箭體結(jié)構(gòu)零件輕量化,因此,輕質(zhì)高強的鋁鋰合金的實際應(yīng)用顯得尤為重要。本文以新一代箭體材料2195鋁鋰合金板材為研究對象,探索熱處理制度與預(yù)變形量對2195鋁鋰合金的微觀組織與力學性能的影響規(guī)律,揭示熱處理強化機制與組織調(diào)控機制,為實際生產(chǎn)工藝制定提供理論依據(jù)與工藝參考。通過硬度測試和拉伸試驗研究了不同熱處理工藝對力學性能的影響,確定最佳固溶處理工藝為520oC×30min,室溫水冷卻,單級時效最佳工藝為160oC×48h,此時屈服強度為417MPa,抗拉強度為493MPa,延伸率為11.3%;分級時效最佳工藝為100oC×8h+160oC×24h,此時屈服強度為534MPa,抗拉強度為571MPa,延伸率為12.8%。分級時效工藝的探究表明:隨預(yù)時效時間的延長,材料到達終時效峰值的時間縮短,但峰值強度有所降低;終時效溫度的提高對終時效的進程無明顯影響,但可以顯著提高強度;終時效時間的延長對強度和塑性的影響根據(jù)終時效溫度的不同有所不同,但大體上強度呈先升后降的趨勢,延伸率呈下降的趨勢。采用透射電鏡(TEM)對材料微觀組織進行分析表明:相比于自然時效的主要析出相δ′相,人工時效的主要析出相T1相為硬質(zhì)相,位錯經(jīng)過時由切過機制轉(zhuǎn)變?yōu)槔@過機制,強化效果更佳;相比于峰時效,過時效時析出相發(fā)生粗化,導致強度降低;相比于單級時效,分級時效過程所析出的T1相更加細小彌散大量,強化效果更好。而時效前預(yù)變形強化的機制是促進位錯及亞晶界的形成,為T1相提供形核位置,促使其彌散均勻的析出,因此強度提高,但由于T1相是脆性相,所以塑性降低。采用掃描電鏡(SEM)對拉伸斷口進行分析,SEM表明退火態(tài)原材料為韌性斷裂,熱處理后的試樣斷口為韌性斷裂或間有準解理斷裂。撕裂棱越明顯,塑性越佳;準解理斷裂占比越大,塑性越差。不同變形量范圍淬火前后的電子背散射衍射(EBSD)分析結(jié)果表明:淬火后發(fā)生了不同程度的再結(jié)晶,且預(yù)變形10%淬火后晶粒發(fā)生了異常長大。晶粒異常長大的原因是淬火過程中由于熱激活的作用,位錯重組程度增大,亞晶界逐漸轉(zhuǎn)變?yōu)榇蠼嵌染Ы�。通過拉伸試驗發(fā)現(xiàn)了預(yù)變形后進行固溶處理的板材會在應(yīng)力-應(yīng)變曲線上出現(xiàn)塑性失穩(wěn)現(xiàn)象-PLC效應(yīng),結(jié)合動態(tài)應(yīng)變時效(DSA)理論分析表明:可動位錯在移動過程中被缺陷和溶質(zhì)原子等阻攔,生成應(yīng)力場,大量溶質(zhì)原子釘扎到可動位錯周圍。只有外加應(yīng)力增加,可動位錯才能克服釘扎,繼續(xù)向前運動。這種溶質(zhì)原子與可動位錯間的反復釘扎、脫釘?shù)倪^程,在應(yīng)力-應(yīng)變曲線上體現(xiàn)出了周期性的鋸齒形波動。
[Abstract]:In order to improve the effective carrying capacity of spaceflight rockets, it is urgent to realize the lightweight structure of rocket arrows. Therefore, the practical application of lightweight and high-strength Al-Li alloys is particularly important. In this paper, the effect of heat treatment and pre-deformation on the microstructure and mechanical properties of 2195 Al-Li alloy was investigated, and the mechanism of heat treatment strengthening and microstructure regulation was revealed. To provide theoretical basis and process reference for actual production process formulation. The effect of different heat treatment processes on mechanical properties was studied by hardness test and tensile test. The optimum solution treatment process was determined as 520oC 脳 30min, water cooled at room temperature. The best process of single stage aging is 160oC 脳 48h, the yield strength is 417MPa, the tensile strength is 493MPa, the elongation is 11.3MPa, and the optimum aging process is 100oC 脳 8h 160oC 脳 24h, the yield strength is 534MPa, the tensile strength is 571MPa, and the elongation is 12.8MPa. The investigation of the graded aging process shows that with the prolongation of the pre-aging time, the time to reach the peak value of the final aging is shortened, but the peak strength is decreased, and the increase of the final aging temperature has no obvious effect on the process of the final aging. The effect of aging time on strength and plasticity was different according to the temperature of final aging, but the strength increased first and then decreased, and the elongation decreased. Transmission electron microscopy (TEM) was used to analyze the microstructure of the material. Compared with the main precipitated phase 未 'phase of natural aging, the main precipitated phase T1 phase of artificial aging was hard phase, and the dislocation was changed from cutting mechanism to bypassing mechanism. Compared with peak aging, the precipitation phase coarsened and the strength decreased. Compared with single-stage aging, the T1 phase precipitated in the step aging process was much smaller and dispersed, and the strengthening effect was better. The mechanism of pre-deformation and strengthening before aging is to promote the formation of dislocation and sub-grain boundary, to provide nucleation position for T1 phase and to promote its dispersion and uniform precipitation, so the strength is increased, but the plasticity decreases because T1 phase is brittle phase. SEM analysis of tensile fracture shows that the annealed raw material is ductile fracture, and the fracture surface after heat treatment is ductile fracture or quasi-cleavage fracture. The more obvious the ripping edge is, the better the plasticity is, and the larger the ratio of quasi-cleavage fracture is, the worse the plasticity is. The results of EBSD analysis before and after quenching in different deformation range showed that recrystallization occurred in different degree after quenching and the grain grew abnormally after 10% pre-deformation quenching. The reason for the abnormal grain growth is that the dislocation recombination degree increases and the sub-grain boundary gradually changes into the large-angle grain boundary due to the effect of thermal activation during quenching. Through the tensile test, it was found that the plastic instability phenomenon appeared on the stress-strain curve of the plate treated by solution treatment after pre-deformation. The theoretical analysis of dynamic strain aging (DSA) shows that the movable dislocation is blocked by defects and solute atoms in the moving process, resulting in a stress field, and a large number of solute atoms are pinned around the movable dislocation. Only when the applied stress increases, can the movable dislocation overcome the pinning and continue to move forward. The process of repeatedly pinning and denailing between solute atoms and movable dislocations shows periodic serrated fluctuations on the stress-strain curves.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.21;TG166.3
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本文編號：1910371