基于厚向组织性能考量的7B50铝合金中厚板回归再时效热处理
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摘要
为解决T6态高强铝合金强度高而耐蚀性难以满足使用需求,采用三级时效工艺来改善析出强化相特别是晶界析出相的形貌、尺寸、分布等,并通过研究不同回归处理制度对组织、性能的影响而获得适宜7B50铝合金中厚板的三级时效工艺.研究发现提高回归温度或延长回归时间均会使中厚板心部及表层组织的晶内和晶界析出相发生粗化并析出稳定η-Mg Zn2相,导致强度下降、电导率上升,其中回归温度对强度和电导率的影响显著.三级时效处理虽使晶内析出相尺寸有所增加,但却使T6态连续分布的晶界析出相呈断续分布,结合心部和表层强度及电导率测量结果认为合适的回归处理制度为165℃/6h.然而,热轧引起中厚板表层较心部更为严重的变形使表层含有更多的亚晶或亚结构且其分布更均匀,从而使表层更快到达峰时效,进一步的回归再时效处理则使表层析出更多稳定η相,而η相的形成与晶内析出相的粗化长大是造成表层和心部强度差异的关键.虽然淬火/三级时效态表层和心部的晶粒结构存在差异,且局部出现亚晶合并长大,但其对强度的提升效果远低于表层析出稳定η相所引起的强度下降.可见,三级时效工艺并不能缓解7B50铝合金中厚板心部和表层的性能差异,但可使表层和心部的强度、电导率满足某实际工况要求.
For enhancing the corrosion resistance of the T6-aged high-strength Al alloys with higher strength,retrogression and reaging( RRA) treatments were used to optimize the morphologies,sizes,distribution of precipitates,especially grain boundary precipitates( GBPs). The effects of different retrogression treatments on the microstructures and mechanical properties were studied so as to gain suitable RRA process for 7B50 Al alloy plates. It is found that increasing the retrogression temperature or time will promote the coarsening of transgranular and intergranular precipitates in the center and surface layers of 7B50 Al alloy plates as well as the precipitation of stable η-Mg Zn2 phase,which will decrease the strength and raise the conductivity. The retrogression temperature will greatly affect the strength and conductivity. The continuously distributed GBPs induced by T6 aging become discontinuous after RRA treatment,accompanying with slightly increasing sizes of transgranular precipitates. Based on the strength and conductivity of the center and surface layers,165 ℃/6 h is the suitable retrogression process for 7B50 Al alloy plates. However,the severe deformation of the surface grains compared to that of the central grains caused by hot rolling leads to a higher content of subgrains or substructures in thesurficial grains,which promotes the surface layer to quickly reach the peak aging,and the subsequent retrogression treatment results in much more stable η phase in the surface layer. The formation of stable η phase as well as the coarsening or growth of transgranular precipitates could be mainly responsible for the strength difference between the surface and center layers. Although there are some differences about the grain structures between the surface and center layers after quenching/RRA treatments with some local subgrain growth,the positive impact of RRA treatment to the strength is apparently unable to compare with the obvious strength reduction caused by early precipitation of stable η phase in the surface layer. Thus,the RRA treatment cannot relieve the property difference between the center and surface layers of 7B50 Al alloy plates,but it can make the strength and conductivity of the center and surface layers to concurrently meet some working requirements.
For enhancing the corrosion resistance of the T6-aged high-strength Al alloys with higher strength,retrogression and reaging( RRA) treatments were used to optimize the morphologies,sizes,distribution of precipitates,especially grain boundary precipitates( GBPs). The effects of different retrogression treatments on the microstructures and mechanical properties were studied so as to gain suitable RRA process for 7B50 Al alloy plates. It is found that increasing the retrogression temperature or time will promote the coarsening of transgranular and intergranular precipitates in the center and surface layers of 7B50 Al alloy plates as well as the precipitation of stable η-Mg Zn2 phase,which will decrease the strength and raise the conductivity. The retrogression temperature will greatly affect the strength and conductivity. The continuously distributed GBPs induced by T6 aging become discontinuous after RRA treatment,accompanying with slightly increasing sizes of transgranular precipitates. Based on the strength and conductivity of the center and surface layers,165 ℃/6 h is the suitable retrogression process for 7B50 Al alloy plates. However,the severe deformation of the surface grains compared to that of the central grains caused by hot rolling leads to a higher content of subgrains or substructures in thesurficial grains,which promotes the surface layer to quickly reach the peak aging,and the subsequent retrogression treatment results in much more stable η phase in the surface layer. The formation of stable η phase as well as the coarsening or growth of transgranular precipitates could be mainly responsible for the strength difference between the surface and center layers. Although there are some differences about the grain structures between the surface and center layers after quenching/RRA treatments with some local subgrain growth,the positive impact of RRA treatment to the strength is apparently unable to compare with the obvious strength reduction caused by early precipitation of stable η phase in the surface layer. Thus,the RRA treatment cannot relieve the property difference between the center and surface layers of 7B50 Al alloy plates,but it can make the strength and conductivity of the center and surface layers to concurrently meet some working requirements.
引文
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[14]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.Acta Mater,2010,58(14):4814
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[16]Zhong L,Ma Y Y,Xie Y C.The Production Technique for Aluminum Alloy Plate.Beijing:Metallurgical Industry Press,2009(钟利,马英义,谢延翠.铝合金中厚板生产技术.北京:冶金工业出版社,2009)
[17]Ma C Q,Hou L G,Zhang J S,et al.Experimental and numerical investigations of the plastic deformation during multi-pass asymmetric and symmetric rolling of high-strength aluminum alloys.Mater Sci Forum,2014,794-796:1157
[18]Tsai T C,Chuang T H.Relationship between electrical conductivity and stress corrosion cracking susceptibility of Al 7075 and Al 7475 alloys.Corrosion,1996,52(6):414
[19]Dumont D,Deschamps A,Brechet Y.On the relationship between microstructure,strength and toughness in AA7050 aluminum alloy.Mater Sci Eng A,2003,356(1):326
[20]Sha G,Cerezo A.Early-stage precipitation in Al-Zn--Mg--Cu alloy(7050).Acta Mater,2004,52(15):4503
[21]Ning A L.Effect of Precipitates and its Distribution on Mechanical Properties of High-strength Aluminum Alloy[Dissertation].Changsha:Central South University,2007(宁爱林.析出相及其分布对高强铝合金力学性能的影响[学位论文].长沙:中南大学,2007)
[22]Song R.G,Dietzel W,Zhang B J,et al.Stress corrosion cracking and hydrogen embrittlement of an Al--Zn-Mg--Cu Alloy.Acta Mater,2004,52(16):4727
[23]Meng Q C,Fan X G,Ren S Y,et al.Comparison of microstructure and corrosion properties of Al--Zn-Mg-Cu alloys 7150 and7010.Trans Nonferrous Met Soc China,2006,16(A3):s1356
[24]Yu Y N.Principles of Metal Science.Beijing:Metallurgical Industry Press,2000(余永宁.金属学原理.北京:冶金工业出版社,2000)
[25]Huo W T,Hou L G,Lang Y J,et al.Improved thermo-mechanical processing for effective grain refinement of high-strength AA7050 Al alloy.Mater Sci Eng A,2015,626:86
[26]El-Baradie Z M,El-Sayed M.Effect of double thermomechanical treatments on the properties of 7075 Al alloy.J Mater Process Technol,1996,62(1):76
[27]Berg L K,Gjnnes J,Hansen V,et al.GP-zones in Al--Zn--Mg alloys and their role in artificial aging.Acta Mater,2001,49(17):3443
[28]Buha J,Lumley R N,Crosky A G.Secondary ageing in an aluminium alloy 7050.Mater Sci Eng A,2008,492(1):1
[29]Kumar M,Poletti C,Degischer H P.Precipitation kinetics in warm forming of AW-7020 alloy.Mater Sci Eng A,2013,561:362
[2]Heinz A,Haszler A,Keidel C,et al.Recent development in aluminium alloys for aerospace applications.Mater Sci Eng A,2000,280(1):102
[3]Williams J C,Jr Starke E A.Progress in structural materials for aerospace systems.Acta Mater,2003,51(19):5775
[4]Tian F Q,Li N K,Cui J Z.Research and development of ultra high strength aluminum alloys.Light Alloy Fabr Technol,2005,33(12):1(田福泉,李念奎,崔建忠.超高强铝合金强韧化的发展过程及方向.轻合金加工技术,2005,33(12):1)
[5]Spiedel M O.Stress corrosion cracking of aluminum alloys.Metall Trans A,1975,6:631
[6]Osaki S,Itoh D,Nakai M.SCC properties of 7050 series aluminum alloys in T6 and RRA tempers.Jpn Inst Light Met,2001,51(4):222
[7]Ramgopal T,Gouma P I,Frankel G S.Role of grain-boundary precipitates and solute depleted zone on the intergranular corrosion of aluminum alloy 7150.Corrosion,2002,58(8):687
[8]Puiggali M,Zienlinski A,Olive J M,et al.Effect of microstructure on stress corrosion cracking of an Al--Zn--Mg--Cu alloy.Corros Sci,1998,40(4):805
[9]Cina B M.Reducing the Susceptibility of Alloys,Particularly Aluminium Alloys,to Stress Corrosion Cracking:US Patent,3856584.1974-12-24
[10]Kanno M,Araki I,Cui Q.Precipitation behaviour of 7000 alloys during retrogression and reaging treatment.Mater Sci Technol,1994,10:599
[11]Park J K.Influence of retrogression and reaging treatments on the strength and stress corrosion resistance of aluminium alloy 7075-T6.Mater Sci Eng A,1988,103(2):223
[12]Robinson J S,Tanner D A,Whelan S D.Retrogression,reaging and residual stresses in 7010 forgings.Fatigue Fract Eng Mater Struct,1999,22(1)51
[13]Viana F,Pinto A M P,Santos H M C,et al.Retrogression and re-ageing of 7075 aluminium alloy:microstructural characterization.J Mater Process Technol,1999,92-93:54
[14]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.Acta Mater,2010,58(14):4814
[15]Li G F,Zhang X M,Li P H,et al.Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050.Trans Nonferrous Met Soc China,2010,20(6):935
[16]Zhong L,Ma Y Y,Xie Y C.The Production Technique for Aluminum Alloy Plate.Beijing:Metallurgical Industry Press,2009(钟利,马英义,谢延翠.铝合金中厚板生产技术.北京:冶金工业出版社,2009)
[17]Ma C Q,Hou L G,Zhang J S,et al.Experimental and numerical investigations of the plastic deformation during multi-pass asymmetric and symmetric rolling of high-strength aluminum alloys.Mater Sci Forum,2014,794-796:1157
[18]Tsai T C,Chuang T H.Relationship between electrical conductivity and stress corrosion cracking susceptibility of Al 7075 and Al 7475 alloys.Corrosion,1996,52(6):414
[19]Dumont D,Deschamps A,Brechet Y.On the relationship between microstructure,strength and toughness in AA7050 aluminum alloy.Mater Sci Eng A,2003,356(1):326
[20]Sha G,Cerezo A.Early-stage precipitation in Al-Zn--Mg--Cu alloy(7050).Acta Mater,2004,52(15):4503
[21]Ning A L.Effect of Precipitates and its Distribution on Mechanical Properties of High-strength Aluminum Alloy[Dissertation].Changsha:Central South University,2007(宁爱林.析出相及其分布对高强铝合金力学性能的影响[学位论文].长沙:中南大学,2007)
[22]Song R.G,Dietzel W,Zhang B J,et al.Stress corrosion cracking and hydrogen embrittlement of an Al--Zn-Mg--Cu Alloy.Acta Mater,2004,52(16):4727
[23]Meng Q C,Fan X G,Ren S Y,et al.Comparison of microstructure and corrosion properties of Al--Zn-Mg-Cu alloys 7150 and7010.Trans Nonferrous Met Soc China,2006,16(A3):s1356
[24]Yu Y N.Principles of Metal Science.Beijing:Metallurgical Industry Press,2000(余永宁.金属学原理.北京:冶金工业出版社,2000)
[25]Huo W T,Hou L G,Lang Y J,et al.Improved thermo-mechanical processing for effective grain refinement of high-strength AA7050 Al alloy.Mater Sci Eng A,2015,626:86
[26]El-Baradie Z M,El-Sayed M.Effect of double thermomechanical treatments on the properties of 7075 Al alloy.J Mater Process Technol,1996,62(1):76
[27]Berg L K,Gjnnes J,Hansen V,et al.GP-zones in Al--Zn--Mg alloys and their role in artificial aging.Acta Mater,2001,49(17):3443
[28]Buha J,Lumley R N,Crosky A G.Secondary ageing in an aluminium alloy 7050.Mater Sci Eng A,2008,492(1):1
[29]Kumar M,Poletti C,Degischer H P.Precipitation kinetics in warm forming of AW-7020 alloy.Mater Sci Eng A,2013,561:362