时效状态对7020铝合金疲劳性能的影响
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摘要
研究不同时效状态下7020铝合金的疲劳强度及疲劳裂纹扩展性能,并分别利用透射电镜和扫描电镜对合金的显微组织及疲劳断口进行观察分析。研究结果表明:欠时效、峰时效和过时效3种时效态合金在循环数为107次时的条件疲劳极限分别为131,114和127 MPa;欠时效合金具有最低的疲劳裂纹扩展速率,峰时效合金的疲劳裂纹扩展速率最高;随着时效程度加大,过时效合金的疲劳裂纹扩展性能有所改善;欠时效合金中可切过的GP区增加位错滑移的可逆性并促进裂纹的偏折,而峰时效合金中主要为η'相,不可切过的η'相以及较大的晶内和晶界无析出带(PFZ)之间的强度差导致疲劳裂纹容易萌生和扩展;过时效合金晶内晶界强度差减小以及相关的裂纹闭合机制使其疲劳性能得到改善。
The fatigue strength and fatigue crack growth behavior of 7020 aluminum alloy under different aging conditions were investigated. The microstructures and fractographies of the alloy were examined by transmission electron microscopy(TEM) and scanning electron microscopy(SEM). The results show that when cycle number is 107, the fatigue strength of 7020 aluminum alloy in under-aged, peak-aged and over-aged conditions are 131, 114 and 127 MPa,respectively. The fatigue crack growth rate of under-aged alloy is the least and that of peak aged alloy is the highest. With the increase of aging degree, the fatigue crack growth property of over aged alloy is improved. The shearable GP zones in under-aged alloy enhance the reversibility of dislocation slip and induce the deflection of fatigue crack. In contrast, the non-shearable η' is dominant in peak aged alloy. Together with the large strength differential between grain interior and precipitation free zone(PFZ) of grain boundary, the non-shearable η' makes the fatigue crack easy to initiate and propagate.The reduction of strength differential and related crack closure mechanisms improve fatigue behavior of over aged alloy.
The fatigue strength and fatigue crack growth behavior of 7020 aluminum alloy under different aging conditions were investigated. The microstructures and fractographies of the alloy were examined by transmission electron microscopy(TEM) and scanning electron microscopy(SEM). The results show that when cycle number is 107, the fatigue strength of 7020 aluminum alloy in under-aged, peak-aged and over-aged conditions are 131, 114 and 127 MPa,respectively. The fatigue crack growth rate of under-aged alloy is the least and that of peak aged alloy is the highest. With the increase of aging degree, the fatigue crack growth property of over aged alloy is improved. The shearable GP zones in under-aged alloy enhance the reversibility of dislocation slip and induce the deflection of fatigue crack. In contrast, the non-shearable η' is dominant in peak aged alloy. Together with the large strength differential between grain interior and precipitation free zone(PFZ) of grain boundary, the non-shearable η' makes the fatigue crack easy to initiate and propagate.The reduction of strength differential and related crack closure mechanisms improve fatigue behavior of over aged alloy.
引文
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[12] CHEN Junzhou, ZHEN Liang, YANG Shoujie, et al.Investigation of precipitation behavior and related hardening in AA 7055 aluminum alloy[J]. Materials Science&Engineering A,2009, 500(1/2):34-42.
[13] KOVáCS I, LENDVAI J, UNGAR T, et al. Mechanical properties of Al ZnMg alloys[J]. Acta Metallurgica, 1980, 28(12):1621-1631.
[14] GURBUZ R, SARIOGLU F. Fatigue crack growth behaviour in aluminium alloy 7475 under different aging conditions[J].Materials Science and Technology, 2001, 17(12):1539-1543.
[15] XIA Peng, LIU Zhiyi, BAI Song, et al. Enhanced fatigue crack propagation resistance in a superhigh strength Al-Zn-Mg-Cu alloy by modifying RRA treatment[J]. Materials Characterization,2016, 118(7):438-445.
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[17] ISO 12107:2012(E), Metallic materials-fatigue testing-statistical planning and analysis of data[S].
[18]束德林.工程材料力学性能[M]. 2版.北京:机械工业出版社,2007:113-115.SHU Delin. Mechanical properties of engineering materials[M].2nd ed. Beijing:China Machine Press, 2007:113-115.
[19]薛喜丽,郑子樵,胡芳,等.时效制度对2A97铝锂合金疲劳裂纹扩展速率的影响[J].稀有金属材料与工程, 2016, 45(12):3319-3324.XUE Xili, ZHEN Ziqiao, HU Fang, et al. Effect of aging conditions on the fatigue crack propagation rate of 2A97aluminum-lithium alloy[J]. Rare Metal Materials and Engineering, 2016, 45(12):3319-3324.
[20]韩念梅. 7050铝合金厚板断裂韧性的研究[D].长沙:中南大学材料科学与工程学院, 2011:61-63.HAN Nianmei. Investigation on the fracture toughness of 7050aluminum alloy thick plate[D]. Changsha:Central South University. School of Materials Science and Engineering, 2011:61-63.
[21] 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 Materialia, 2010, 58(14):4814-4826.
[22] KAMP N, SINCLAIR I, STARINK M J. Toughness-strength relations in the overaged 7449 al-based alloy[J]. Metallurgical and Materials Transactions A, 2002, 33(4):1125-1136.
[23] CHEN Xu, LIU Zhiyi, LIN Mao, et al. Enhanced Fatigue Crack Propagation Resistance in an Al-Zn-Mg-Cu Alloy by Retrogression and Reaging Treatment[J]. Journal of Materials Engineering and Performance, 2012, 21(11):2345-2353.
[24] SURESH S, VASUDéVAN A K, BRETZ P E. Mechanisms of slow fatigue crack growth in high strength aluminum alloys:role of microstructure and environment[J]. Metallurgical&Materials Transactions A, 1984, 15(2):369-379.
[2]杨涛,叶凌英,刘胜胆,等.预时效对7020铝合金组织与性能的影响[J].中南大学学报(自然科学版), 2017, 48(3):578-584.YANG Tao, YE Lingying, LIU Shengdan, et al. Effect of pre-aging on microstructures and mechanical properties of 7020aluminum alloy[J]. Journal of Central South University(Science and Technology), 2017, 48(3):578-584.
[3]周明哲,易丹青,王斌,等.固溶处理对2E12铝合金组织及疲劳断裂行为的影响[J].中南大学学报(自然科学版), 2012,43(1):66-73.ZHOU Mingzhe, YI Danqing, WANG Bin, et al. Effect of solution treatment on fatigue behavior of 2E12 aluminum alloy[J]. Journal of Central South University(Science and Technology), 2012, 43(1):66-73.
[4] CHEN Junzhou, ZHEN Liang, YANG Shoujie, et al. Effects of precipitates on fatigue crack growth rate of AA 7055 aluminum alloy[J]. Transactions of Nonferrous Metals Society of China,2010, 20(12):2209-2214.
[5] DESMUKH M N, PANDEY R K, MUKHOPADHYAY A K.Effect of aging treatments on the kinetics of fatigue crack growth in 7010 aluminum alloy[J]. Materials Science&Engineering A,2006, 435/436(5):318-326.
[6] DE P S, MISHRA R S, BAUMANN J A. Characterization of high cycle fatigue behavior of a new generation aluminum lithium alloy[J]. Acta Materialia, 2011, 59(15):5946-5960.
[7]陈宇强,宋文炜,潘素平,等. T6I4和T6I6时效处理对7050铝合金疲劳性能的影响[J].中南大学学报(自然科学版), 2016,47(10):3332-3340.CHEN Yuqiang, SONG Wenwei, PAN Suping, et al. Influence of T6I4 and T6I6 aging treatments on fatigue properties of 7050 Al alloy[J]. Journal of Central South University(Science and Technology), 2016, 47(10):3332-3340.
[8] STILLER K, WARREN P J, HANSEN V, et al. Investigation of precipitation in an Al-Zn-Mg alloy after two-step ageing treatment at 100℃and 150℃[J]. Materials Science and Engineering A, 1999, 270(1):55-63.
[9] BERG L K, GJ?NNES J, HANSEN V, et al. GP-zones in Al-Zn-Mg alloys and their role in artificial aging[J]. Acta Materialia, 2001, 49(17):3443-3451.
[10] ENGDAHL T, HANSEN V, WARREN P J, et al. Investigation of fine scale precipitates in Al-Zn-Mg alloys after various heat treatments[J]. Materials Science and Engineering A, 2002,327(1):59-64.
[11] SHA Gang, CEREZO A. Early-stage precipitation in Al-Zn-Mg-Cu alloy(7050)[J]. Acta Materialia, 2004, 52(15):4503-4516.
[12] CHEN Junzhou, ZHEN Liang, YANG Shoujie, et al.Investigation of precipitation behavior and related hardening in AA 7055 aluminum alloy[J]. Materials Science&Engineering A,2009, 500(1/2):34-42.
[13] KOVáCS I, LENDVAI J, UNGAR T, et al. Mechanical properties of Al ZnMg alloys[J]. Acta Metallurgica, 1980, 28(12):1621-1631.
[14] GURBUZ R, SARIOGLU F. Fatigue crack growth behaviour in aluminium alloy 7475 under different aging conditions[J].Materials Science and Technology, 2001, 17(12):1539-1543.
[15] XIA Peng, LIU Zhiyi, BAI Song, et al. Enhanced fatigue crack propagation resistance in a superhigh strength Al-Zn-Mg-Cu alloy by modifying RRA treatment[J]. Materials Characterization,2016, 118(7):438-445.
[16]苏雷什.材料的疲劳[M].王中光,译.北京:国防工业出版社, 1999:343-357.SURESH S. Fatigue of materials[M]. WANG Zhongguang, trans.Beijing:National Defense Industry Press, 1999:343-357.
[17] ISO 12107:2012(E), Metallic materials-fatigue testing-statistical planning and analysis of data[S].
[18]束德林.工程材料力学性能[M]. 2版.北京:机械工业出版社,2007:113-115.SHU Delin. Mechanical properties of engineering materials[M].2nd ed. Beijing:China Machine Press, 2007:113-115.
[19]薛喜丽,郑子樵,胡芳,等.时效制度对2A97铝锂合金疲劳裂纹扩展速率的影响[J].稀有金属材料与工程, 2016, 45(12):3319-3324.XUE Xili, ZHEN Ziqiao, HU Fang, et al. Effect of aging conditions on the fatigue crack propagation rate of 2A97aluminum-lithium alloy[J]. Rare Metal Materials and Engineering, 2016, 45(12):3319-3324.
[20]韩念梅. 7050铝合金厚板断裂韧性的研究[D].长沙:中南大学材料科学与工程学院, 2011:61-63.HAN Nianmei. Investigation on the fracture toughness of 7050aluminum alloy thick plate[D]. Changsha:Central South University. School of Materials Science and Engineering, 2011:61-63.
[21] 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 Materialia, 2010, 58(14):4814-4826.
[22] KAMP N, SINCLAIR I, STARINK M J. Toughness-strength relations in the overaged 7449 al-based alloy[J]. Metallurgical and Materials Transactions A, 2002, 33(4):1125-1136.
[23] CHEN Xu, LIU Zhiyi, LIN Mao, et al. Enhanced Fatigue Crack Propagation Resistance in an Al-Zn-Mg-Cu Alloy by Retrogression and Reaging Treatment[J]. Journal of Materials Engineering and Performance, 2012, 21(11):2345-2353.
[24] SURESH S, VASUDéVAN A K, BRETZ P E. Mechanisms of slow fatigue crack growth in high strength aluminum alloys:role of microstructure and environment[J]. Metallurgical&Materials Transactions A, 1984, 15(2):369-379.