非等温回归再时效对Al-8Zn-2Mg-2Cu合金厚板组织及性能的影响
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摘要
基于铝合金厚板热处理时客观存在的非等温现象,利用非等温回归动力学模型、力学性能测试、电导率测试及TEM观察,研究了非等温回归温度场和时间的耦合效应对Al-8Zn-2Mg-2Cu(质量分数,%)合金厚板组织及性能的影响。结果表明,随着非等温回归时间的延长,合金的电导率逐渐升高,硬度和强度逐渐下降。优化的非等温回归再时效制度使Mg Zn2相的尺寸分布范围宽化。因此,位错切过和位错绕过强化机制的合理匹配有效地降低了硬度的损失,同时合金的电导率得到显著提升。以105℃、24 h为预时效制度,经过慢速升温非等温回归处理120 min后再经120℃、24 h峰时效,Al-8Zn-2Mg-2Cu铝合金厚板的抗拉强度、屈服强度及电导率分别为620 MPa、593 MPa和21.1 MS/m,其综合性能优于单级峰时效(T6)及双级过时效(T73),且包含慢速升温的非等温回归再时效技术更适用于厚板的时效热处理。
7000 series Al alloy has been widely used in aeronautical structural materials because of its high strength, high stress corrosion cracking resistance and good fatigue resistance when treated by retrogression and re-ageing(RRA). Al-8 Zn-2 Mg-2 Cu(mass fraction, %) thick plate is supposed to manufacture the aircraft wing in Chinese big plane project. Due to the non-isothermal environment in the process of heat treatment for aluminum alloy thick plate, the influence of coupling effect of non-isothermal retrogression temperature field and time on the microstructure and properties of Al-8 Zn-2 Mg-2 Cu alloy thick plate was investigated by the non-isothermal kinetic model, mechanical properties tests, electrical conductivity test and TEM observations. The results show that, the electrical conductivity increases while the hardness and strength decrease with the non-isothermal retrogression time increasing. The optimized non-isothermal retrogression and re-ageing(NRRA) treatment makes the size distribution range of Mg Zn2 phase wider. Therefore,the logical matching between the dislocation cutting off mechanism and the dislocation by-passing mechanism effectively reduces the loss of hardness. Meanwhile, the electrical conductivity is significantly improved. After the treatment of 105 ℃, 24 h(pre-ageing) and non-isothermal regression(120 min) with slow heating rate and 120 ℃, 24 h re-ageing, the Al-8 Zn-2 Mg-2 Cu alloy thick plate possesses an excellent comprehensive performance than those of T6 and T73 states. The tensile strength, yield strength and electrical conductivity are 620 MPa, 593 MPa and 21.1 MS/m, respectively.The NRRA treatment with slow heating rate is more suitable for the ageing treatment of thick plate.
7000 series Al alloy has been widely used in aeronautical structural materials because of its high strength, high stress corrosion cracking resistance and good fatigue resistance when treated by retrogression and re-ageing(RRA). Al-8 Zn-2 Mg-2 Cu(mass fraction, %) thick plate is supposed to manufacture the aircraft wing in Chinese big plane project. Due to the non-isothermal environment in the process of heat treatment for aluminum alloy thick plate, the influence of coupling effect of non-isothermal retrogression temperature field and time on the microstructure and properties of Al-8 Zn-2 Mg-2 Cu alloy thick plate was investigated by the non-isothermal kinetic model, mechanical properties tests, electrical conductivity test and TEM observations. The results show that, the electrical conductivity increases while the hardness and strength decrease with the non-isothermal retrogression time increasing. The optimized non-isothermal retrogression and re-ageing(NRRA) treatment makes the size distribution range of Mg Zn2 phase wider. Therefore,the logical matching between the dislocation cutting off mechanism and the dislocation by-passing mechanism effectively reduces the loss of hardness. Meanwhile, the electrical conductivity is significantly improved. After the treatment of 105 ℃, 24 h(pre-ageing) and non-isothermal regression(120 min) with slow heating rate and 120 ℃, 24 h re-ageing, the Al-8 Zn-2 Mg-2 Cu alloy thick plate possesses an excellent comprehensive performance than those of T6 and T73 states. The tensile strength, yield strength and electrical conductivity are 620 MPa, 593 MPa and 21.1 MS/m, respectively.The NRRA treatment with slow heating rate is more suitable for the ageing treatment of thick plate.
引文
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[24]Cui Z Q,Qin Y C.Metallography&Heat Treatment[M].Beijing:Mechanical Industry Press,2012:179(崔忠圻,覃耀春.金属学与热处理[M].北京:机械工业出版社,2012:179)
[25]Lumley R.Fundamentals of Aluminium Metallurgy[M].London:Woodhead Publishing Ltd.,2011:356
[26]Cui X L,Wu Y Y,Zhang G J,et al.Study on the improvement of electrical conductivity and mechanical properties of low alloying electrical aluminum alloys[J].Composites,2017,110B:381
[27]Zhang G Y,Zhang H,Fang G L,et al.Electronic structure of different regions and analysis of stress corrosion mechanism of AlZn-Mg-Cu alloys[J].Acta Metall.Sin.,2009,45:687(张国英,张辉,方戈亮等.Al-Zn-Mg-Cu系铝合金中不同区域电子结构及应力腐蚀机理分析[J].金属学报,2009,45:687)
[2]Zhang X M,Deng Y L,Zhang Y.Development of high strength aluminum alloys and processing techniques for the materials[J].Acta Metall.Sin.,2015,51:257(张新明,邓运来,张勇.高强铝合金的发展及其材料的制备加工技术[J].金属学报,2015,51:257)
[3]Grong?,Shercliff H R.Microstructural modelling in metals processing[J].Prog.Mater.Sci.,2002,47:163
[4]Hutchinson C R,GounéM,Redja?mia.A Selecting non-isothermal heat treatment schedules for precipitation hardening systems:An example of coupled process-property optimization[J].Acta Mater.,2007,55:213
[5]Jiang D M,Liu Y,Liang S,et al.The effects of non-isothermal aging on the strength and corrosion behavior of Al Zn Mg Cu alloy[J].J.Alloys Compd.,2016,681:57
[6]Marlaud T,Deschamps A,Bley F,et al.Evolution of precipitate microstructures during the retrogression and re-ageing heat treatment of an Al-Zn-Mg-Cu alloy[J].Acta Mater.,2010,58:4814
[7]Staley J T.Method and process of non-isothermal aging for aluminum alloys[P].Durham US Pat,0237113Al,2007
[8]Li K,Zhang K,Yang L,et al.Investigation of non-isothermal aging process of 7085 aluminum alloy[A].Proceedings of the 12th International Conference on Aluminium Alloys[C].Yokohama:The Japan Institute of Light Metals,2010:2120
[9]Zhen L,Huang M,Liu M,et al.Effect of cooling method on the microstructure and properties of 7085 aluminum alloy during non-isothermal aging[A].Proceedings of the 12th International Conference on Aluminium Alloys[C].Yokohama:The Japan Institute of Light Metals,2010:481
[10]Jiang J T,Xiao W Q,Yang L,et al.Ageing behavior and stress corrosion cracking resistance of a non-isothermally aged Al-Zn-MgCu alloy[J].Mater.Sci.Eng.,2014,A605:167
[11]Liu Y,Jiang D M,Li B Q,et al.Effect of cooling aging on microstructure and mechanical properties of an Al-Zn-Mg-Cu alloy[J].Mater.Des.,2014,57:79
[12]Liu Y,Jiang D M,Li B Q,et al.Heating aging behavior of Al-8.35Zn-2.5Mg-2.25Cu alloy[J].Mater.Des.,2014,60:116
[13]Peng X Y,Guo Q,Liang X P,et al.Mechanical properties,corrosion behavior and microstructures of a non-isothermal ageing treated Al-Zn-Mg-Cu alloy[J].Mater.Sci.Eng.,2017,A688:146
[14]Koziel J,Blaz L,Wloch G,et al.Precipitation processes during non-isothermal aging of fine-grained AA2219[J].J.Alloys Compd.,2016,682:468
[15]Cina B.Reducing the susceptibility of alloys,particularly aluminium alloys,to stress corrosion cracking[P].US Pat,3856584,1974
[16]Feng D,Zhang X M,Liu S D,et al.The effect of pre-ageing temperature and retrogression heating rate on the microstructure and properties of AA7055[J].Mater.Sci.Eng.,2013,A588:34
[17]Su R M,Qu Y D,Li D R.Pre-aging of retrogression and re-aging of spray formed 7075 alloy[J].Acta Metall.Sin.,2014,50:863(苏睿明,曲迎东,李荣德.喷射态7075合金回归再时效中预时效的研究[J].金属学报,2014,50:863)
[18]Starink M J,Li X M.A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys[J].Metall.Mater.Trans.,2003,34A:899
[19]Chen J Z.Ageing precipitation behavior and mechanical properties of AA7055 aluminum alloy[D].Harbin:Harbin Institute of Technology,2008(陈军洲.AA7055铝合金的时效析出行为与力学性能[D].哈尔滨:哈尔滨工业大学,2008)
[20]Feng D,Zhang X M,Liu S D,et al.Effect of pre-aging temperature and retrogression heating rate on microstructure and properties of 7150 alloy[J].Chin.J.Nonferrous Met.,2013,23:1173(冯迪,张新明,刘胜胆等.预时效温度及回归加热速率对7150铝合金显微组织及性能的影响[J].中国有色金属学报,2013,23:1173)
[21]Ning A L,Liu Z Y,Feng C,et al.Analysis on the behavior of exceeding peak aging strength of aluminum alloy at condition of retrogression and reaging[J].Acta Metall.Sin.,2006,42:1253(宁爱林,刘志义,冯春等.铝合金回归再时效状态的超峰时效强度行为分析[J].金属学报,2006,42:1253)
[22]Feng D,Zhang X M,Liu S D,et al.Non-isothermal retrogression kinetics for grain boundary precipitate of 7A55 aluminum alloy[J].Trans.Nonferrous Met.Soc.China,2014,24:2212
[23]Feng D,Zhang X M,Liu S D,et al.Non-isothermal“retrogression and re-ageing”treatment schedule for AA7055 thick plate[J].Mater.Des.,2014,60:208
[24]Cui Z Q,Qin Y C.Metallography&Heat Treatment[M].Beijing:Mechanical Industry Press,2012:179(崔忠圻,覃耀春.金属学与热处理[M].北京:机械工业出版社,2012:179)
[25]Lumley R.Fundamentals of Aluminium Metallurgy[M].London:Woodhead Publishing Ltd.,2011:356
[26]Cui X L,Wu Y Y,Zhang G J,et al.Study on the improvement of electrical conductivity and mechanical properties of low alloying electrical aluminum alloys[J].Composites,2017,110B:381
[27]Zhang G Y,Zhang H,Fang G L,et al.Electronic structure of different regions and analysis of stress corrosion mechanism of AlZn-Mg-Cu alloys[J].Acta Metall.Sin.,2009,45:687(张国英,张辉,方戈亮等.Al-Zn-Mg-Cu系铝合金中不同区域电子结构及应力腐蚀机理分析[J].金属学报,2009,45:687)