热处理及预变形对2195铝锂合金板材组织性能的影响

发布时间：2018-05-19 13:57

  本文选题：2195铝锂合金 + 分级时效　； 参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：为提高航天火箭的有效运载能力,迫切需要实现火箭箭体结构零件轻量化,因此,轻质高强的铝锂合金的实际应用显得尤为重要。本文以新一代箭体材料2195铝锂合金板材为研究对象,探索热处理制度与预变形量对2195铝锂合金的微观组织与力学性能的影响规律,揭示热处理强化机制与组织调控机制,为实际生产工艺制定提供理论依据与工艺参考。通过硬度测试和拉伸试验研究了不同热处理工艺对力学性能的影响,确定最佳固溶处理工艺为520oC×30min,室温水冷却,单级时效最佳工艺为160oC×48h,此时屈服强度为417MPa,抗拉强度为493MPa,延伸率为11.3%;分级时效最佳工艺为100oC×8h+160oC×24h,此时屈服强度为534MPa,抗拉强度为571MPa,延伸率为12.8%。分级时效工艺的探究表明:随预时效时间的延长,材料到达终时效峰值的时间缩短,但峰值强度有所降低;终时效温度的提高对终时效的进程无明显影响,但可以显著提高强度;终时效时间的延长对强度和塑性的影响根据终时效温度的不同有所不同,但大体上强度呈先升后降的趋势,延伸率呈下降的趋势。采用透射电镜(TEM)对材料微观组织进行分析表明:相比于自然时效的主要析出相δ′相,人工时效的主要析出相T1相为硬质相,位错经过时由切过机制转变为绕过机制,强化效果更佳;相比于峰时效,过时效时析出相发生粗化,导致强度降低;相比于单级时效,分级时效过程所析出的T1相更加细小弥散大量,强化效果更好。而时效前预变形强化的机制是促进位错及亚晶界的形成,为T1相提供形核位置,促使其弥散均匀的析出,因此强度提高,但由于T1相是脆性相,所以塑性降低。采用扫描电镜(SEM)对拉伸断口进行分析,SEM表明退火态原材料为韧性断裂,热处理后的试样断口为韧性断裂或间有准解理断裂。撕裂棱越明显,塑性越佳;准解理断裂占比越大,塑性越差。不同变形量范围淬火前后的电子背散射衍射(EBSD)分析结果表明:淬火后发生了不同程度的再结晶,且预变形10%淬火后晶粒发生了异常长大。晶粒异常长大的原因是淬火过程中由于热激活的作用,位错重组程度增大,亚晶界逐渐转变为大角度晶界。通过拉伸试验发现了预变形后进行固溶处理的板材会在应力-应变曲线上出现塑性失稳现象-PLC效应,结合动态应变时效(DSA)理论分析表明:可动位错在移动过程中被缺陷和溶质原子等阻拦,生成应力场,大量溶质原子钉扎到可动位错周围。只有外加应力增加,可动位错才能克服钉扎,继续向前运动。这种溶质原子与可动位错间的反复钉扎、脱钉的过程,在应力-应变曲线上体现出了周期性的锯齿形波动。
[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.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21;TG166.3
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本文编号：1910371