【作者】 黄志其；

【导师】 尹志民；

【作者基本信息】 中南大学 ， 材料物理与化学， 2013， 博士

【摘要】 在工业化生产条件下,经过熔铸、均匀化及挤压得到了几种轨道交通用主要6xxx和7xxx工业铝合金的棒材,通过力学性能测试、电导率测试,显微组织分析和计算机软件模拟等方法研究了可实现在线淬火的主要轨道交通用工业铝合金的固溶-时效制度,采用等温-淬火-电导率测试和等温-淬火-时效-硬度测试获得合金的TTT和TTP曲线,之后利用Jmat Pro软件计算出6XXX系和7XXX系5个合金的TTT和CCT曲线,并与实验研究得到的有关参数进行对比分析,再利用Jmat Pro软件得到的合金物理参数,应用于Abaqus软件,来模拟不同淬火条件下合金的应力分布情况,旨在为确定这些合金在线淬火工艺提供实验依据。最后,设计研制了一套在线淬火装置,来实际考察研究合金的在线淬火特性。实验结果表明：(1)6005A合金适宜的固溶-时效制度为535℃×50mmin固溶,水淬,180℃×6h时效,在此条件下,6005A合金的抗拉强度、屈服强度和伸长率分别为329MPa、305MPa和14%。(2)6005A合金TTT曲线和TTP曲线呈“C”型,鼻尖温度在340℃附近,孕育时间为9s,淬火敏感性高,合金在340℃等温处理的相变动力学方程为：f=1-exp(-0.006t0.9457)；6005A合金等温保温过程中过饱和固溶体分解析出第二相粒子,在鼻尖温度340℃达到最大的脱溶速率,合金的析出序列为：过饱和固溶体-p”-p’-p。(3)7005合金热挤压棒材合宜的离线固溶-时效制度为470℃/30min固溶水淬和105℃/10h+145℃/10h双级时效,在此条件下,合金棒材的抗拉强度、屈服强度、延伸率分别为480Mpa、451Mpa和8.4%。在优先考虑合金强度的前提下,时效各因素对合金性能影响的主次关系为：A>C>B>D,即一级时效温度>二级时效温度>一级时效时间>二级时效时间。(4)7005合金的TTT和TTP曲线都呈“C”形,C曲线鼻尖温度为285℃,C曲线鼻尖温度附近,固溶体分解对应的相转变孕育期极短,固溶体容易分解,即淬火敏感性高,而低温区及高温区淬火敏感性较低。7005型材生产在线挤压后淬火时,高温及低温区域可以适当降低冷却速度,而在鼻尖温度区域其冷却速度应该尽量大于6℃／s,以抑制各种物相的析出,保证其具有较好的综合性能。(5) Jmat pro软件通过计算模拟出主要6xxx和7xxx合金的TTT曲线及CCT曲线,给出了抑制不同合金不同析出相析出的最小淬火冷却速度,与淬火因子分析方法所得到的最小冷却速度基本一致,为在线淬火工艺提供理论和实际指导。(6) Abaqus CAE软件利用Jmatpro软件模拟计算出的合金相关物理量,可以模拟出合金在不同淬火制度下的温度场及应力场。分段淬火与一次性淬火相比,在保证合金性能基本不下降的同时,能够大幅度减小合金的内应力。(7)6005A型材生产在线挤压后淬火时,型材出口温度(相当于在线淬火温度)最好大于500℃,自500℃以上冷却到分解危险温度415℃时,可以适当慢速,随后要以9℃/s快速淬火通过280～415℃淬火敏感区,在低温区域再适当提高冷却速度。(8)6061合金在在250-450℃范围内淬火敏感性高,合金中β相无析出的临界冷却速度约为2℃/s,β”相和p’相无析出的临界冷却速度约为9℃/s。因此对于6061合金其冷却速度应该尽量大于9℃/s,以抑制p相、p’相和p”相的析出保证其具有较好的综合性能。(9)6082合金在340-360℃范围内淬火敏感性高,合金中p相的无析出临界冷却速度约为3℃/s,p”相和β’相的无析出临界冷却速度约为15℃/s。因此合金淬火冷却速度应该尽量大于15℃/s,以抑制p相、p’相和p”相的析出保证其具有较好的综合性能。(10)7003合金淬火敏感区间为250-330℃,η’相的析出敏感鼻尖温度为270℃,η’相的无析出临界冷却速度约为1℃/s,因此对于7003合金其冷却速度应该在1℃/s左右,以抑制各种物相的析出保证其具有较好的综合性能。(11)在前期研究的基础上,开发了一套精密在线水-雾-风淬火系统,可以实现周向分区控制,轴向分段控制冷却,并可对某一冷却参数以模具编号形式进行存储,在后续生产可实现直接调用,满足主要轨道交通用6xxx和7xxx工业合金的淬火要求。更多还原

【Abstract】 Some round bar of6xxx and7xxx alloys for rail vehicle use were produced through smelting&casting, homogenization and extrusion under industrial condition. The reasonable solution&aging process and quench sensitivities of main industrial alloys for rail vehicle use were investigated through mechanical property test, electrical conductivity test, and microstructure analysis as well as computer software simulation. The TTT and TTP curve of these alloys were obtained based on all of the experimental data, and then the results were compared with those of computer simulation. the effect of different cooling rate to the inner stress was analyzed through finite element analysis software. At last,A precise on-line water-miss-wind quenching system were developed under the research which was used in real production line to the sensitivity evaluation. the results shows that:(1) The suitable solution-aging system of6005A alloy is535℃×50min solid solution and water quenching,180℃×6h aging. In this condition, the6005A alloy tensile strength, yield strength and elongation are329MPa,305MPa and14%.(2) The TTT curve and TTP curve of6005A alloy are "C" type, the nose temperature is340℃, the time of gave birth is9s,6005A alloy has high quench sensitivity, The phase transformation kinetics equation of6005A alloy at340℃isothermal treatment is f=1-exP(-0.006t0.9457.)The supersaturated solid solution of6005A alloy decompose and precipitate second phase particles during the isothermal process, and has the maximum rate at the tip temperature of340℃,6005A alloy precipitation sequence is:supersaturated solid solution-β"-β’-β.(3) The best solution quenching and aging technology of extrusion bar of7005alloy is470℃/30min solution, water quenching and with two step aging of105℃/10h+145℃/10h, under this condition, the tensile strength, yield strength and elongation of alloy bar can get to480Mpa,451Mpa and8.4%respectively. Take alloy strength as priority, the effect of every factor of aging process to strength is A>C>B>D, that is:the aging temperature of the first step> the aging temperature of the second step> the aging time of the first step> the aging time of the second step.(4) The TTT curve and TTP curve of7005alloy are"C" type, the nose temperature is285℃, and the incubation period of phase transformation corresponding to the decomposition of solid solution is extremly short in the nose area, which menns that it has very high quenching sensitivity, but it has low quenching sensitivity in the area of high temperature and low temperature. During the on-line quenching, the quenching rate can slow down in the area of high temperature and low temperature, but the quenching rate should exceed6℃/s in the nose area, so as to restrain the presipitates of phase, and ensure the synthesis property of alloy.(5) The TTT and CCT curve of main6xxx and7xxx alloy were simulated and calculated through Jmatpro5.1software, and the results are the same with those obtained by experiment.(6) Abaqus CAE software can simulate the temperature field and stress field at different quenching systems through the curves of physical parameters changing with temperature which get from JmatPro5.1software. Compared with the one-time quenching section, to ensure the basic performance is not declining, sub-quenching can reduce the stress of the alloy.(7) The outlet temperature (the equivalent of online quenching temperature) of6005A profile alloy should be higher than500℃after online extrusion quenching. The speed can be slowed down from500℃to415℃, and higher than9℃/s form415℃to280quenching sensitive areas. For one thing, this can reduce the residual stress. For another, this can avoid the decomposition of solid solution, which can guarantee the mechanical properties.(8) The quenching sensitivity of6061alloy is very high bettween the temperature of250～450℃, and the criticle cooling rate to prevent the precipitate of (3phase is2℃/s, and9℃/s for β" and β’ phase, so for6061Al-alloy the quench rate should be more than9℃/s at the quench sensitivity temperature zone (250～450℃) so as to gain the best properties.(9) The quenching sensitivity of6082alloy is very high bettween the temperature of340～360℃, and the criticle cooling rate to prevent the precipitate of β phase is3℃/s, and15℃/s for β" and β’ phase, so for6082Al-alloy the quench rate should be more than15℃/s at the quench sensitivity temperature zone so as to gain the best properties.(10) The quenching sensitivity of7003alloy is very high bettween the temperature of250～330℃, and the criticle cooling rate to prevent the precipitate of η’ phase is1℃/s, so for7003Al-alloy the quench rate should be more than1℃/s at the quench sensitivity temperature zone so as to gain the best properties.(11) An precise on-line water-mist-wind quenching system was developed based on the former research. And it can be precise controlled in different direction in the circle and axis, and the cooling data can be stored in the form of the die number, and could directly used the next time during production, and could satisfy the quenching requierment of main6xxx and7xxx alloy for industrial use.更多还原