半连续铸造7136超高强铝合金的组织特征及均匀化处理工艺
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摘要
以半连续铸造7136铝合金为研究对象,以铸态组织分析为基础,采用双级均匀化.结果表明:与其他7×××系铝合金相比,7136铝合金铸态组织没有明显的层片状α(Al)+T共晶相的特征,也没有发现S相的存在.基体中的弥散相为微米级的圆形或棒状MgZn2相,Mg元素和Zn元素随着液态合金的凝固,在Al基体中以MgZn_2相的形式析出,为了平衡Mg元素和Zn元素的分配系数,Mg元素和Zn元素从液态向固态迁移,这也是使得晶内Zn元素和Mg元素偏高的原因.经过462℃,24 h单级均匀化,残留相大致消除.随着均匀化时间的延长,残留相有减少的趋势,但作用相对较小.经过450℃,24 h+470℃,24 h双级均匀化,差示扫描量热法获取的峰值非常小,晶间除了少量高熔点Al_7Cu_2Fe相残留,Al_2Cu等其他相已基本消除,均匀化效果显著.
The 7 × × × series aluminum alloy is mainly produced using semi-continuous water-cooled casting with this method,the solidification speed of the alloy is fast,leading to different degrees of dendrite segregation and non-equilibrium eutectic structure in the ingot. This also results in non-uniformity of composition and structure. Further,it adversely affects the subsequent cutting process and comprehensive performance of the alloy. Therefore,ingot homogenization becomes an indispensable and very critical process for the elimination of segregation. There is much research on Al-Zn-Mg-Cu alloys at home and abroad at the present. This research mainly concentrates on alloys such as 7075,7050,7150 and 7055. The content of the main alloying elements of these alloys is mostly around10%. However,at present,there is not much research on alloy materials with a strength and main alloying element content exceeding12. 5%. The main alloy element content of 7136 aluminum alloy is about 13. 5%. In 7136 aluminum alloy,the main alloy element content is high and the cast microstructure characteristics and homogenization treatment conditions are very different from other 7 × × ×series aluminum alloys. In this paper,semi-continuous casting 7136 aluminum alloy was taken as the research object,based on the ascast microstructure analysis,using two-stage homogenization. The results show that,compared with the other 7 × × × series aluminum alloys,the cast microstructure of 7136 aluminum alloy has no obvious lamellar Al( Al) + T eutectic phase characteristics,and no S phase exists. The dispersed phase in the matrix is a micron-sized round or rod-shaped MgZn2 phase. The Mg and Zn were precipitated as MgZn2 phase in the Al matrix as the liquid alloy solidified. In order to balance the partition coefficients of the Mg and Zn,the two metals converted from the liquid to the solid state,which explained why the Zn and Mg crystal contents were high. After a single stage of homogenization at 462 ℃,24 h,the residual phase was substantially eliminated. As the homogenization time increased,the residual phase tended to decrease,but the effect was relatively small by this method. After the 7136 aluminum alloy was homogenized for two stages at 450 ℃,24 h and 470 ℃,24 h. The peak values obtained by differential scanning calorimetry were very small,except for a small amount of high-melting Al_7 Cu_2 Fe phase remaining between the crystals. Al_2Cu and other phases were basically eliminated and the homogenization effect was significant.
The 7 × × × series aluminum alloy is mainly produced using semi-continuous water-cooled casting with this method,the solidification speed of the alloy is fast,leading to different degrees of dendrite segregation and non-equilibrium eutectic structure in the ingot. This also results in non-uniformity of composition and structure. Further,it adversely affects the subsequent cutting process and comprehensive performance of the alloy. Therefore,ingot homogenization becomes an indispensable and very critical process for the elimination of segregation. There is much research on Al-Zn-Mg-Cu alloys at home and abroad at the present. This research mainly concentrates on alloys such as 7075,7050,7150 and 7055. The content of the main alloying elements of these alloys is mostly around10%. However,at present,there is not much research on alloy materials with a strength and main alloying element content exceeding12. 5%. The main alloy element content of 7136 aluminum alloy is about 13. 5%. In 7136 aluminum alloy,the main alloy element content is high and the cast microstructure characteristics and homogenization treatment conditions are very different from other 7 × × ×series aluminum alloys. In this paper,semi-continuous casting 7136 aluminum alloy was taken as the research object,based on the ascast microstructure analysis,using two-stage homogenization. The results show that,compared with the other 7 × × × series aluminum alloys,the cast microstructure of 7136 aluminum alloy has no obvious lamellar Al( Al) + T eutectic phase characteristics,and no S phase exists. The dispersed phase in the matrix is a micron-sized round or rod-shaped MgZn2 phase. The Mg and Zn were precipitated as MgZn2 phase in the Al matrix as the liquid alloy solidified. In order to balance the partition coefficients of the Mg and Zn,the two metals converted from the liquid to the solid state,which explained why the Zn and Mg crystal contents were high. After a single stage of homogenization at 462 ℃,24 h,the residual phase was substantially eliminated. As the homogenization time increased,the residual phase tended to decrease,but the effect was relatively small by this method. After the 7136 aluminum alloy was homogenized for two stages at 450 ℃,24 h and 470 ℃,24 h. The peak values obtained by differential scanning calorimetry were very small,except for a small amount of high-melting Al_7 Cu_2 Fe phase remaining between the crystals. Al_2Cu and other phases were basically eliminated and the homogenization effect was significant.
引文
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[11]Mahathaninwong N,Plookphol T,Wannasin J,et al.T6 heat treatment of rheocasting 7075 Al alloy.Mater Sci Eng A,2012,532:91
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[13]Li J F,Peng Z W,Li C X,et al.Mechanical properties,corrosion behaviors and microstructures of 7075 aluminium alloy with various aging treatments.Trans Nonferrous Met Soc China,2008,18(4):755
[14]Liu Y,Jiang D M,Xie W L,et al.Solidification phases and their evolution during homogenization of a DC cast Al-8.35Zn-2.5Mg--2.25Cu alloy.Mater Charact,2014,93:173
[15]Wen K,Xiong B Q,Fan Y Q,et al.Transformation and dissolution of second phases during solution treatment of an Al--Zn-Mg--Cu alloy containing high zinc.Rare Met,2018,37(5):376
[2]Williams J C,Starke Jr E A.Progress in structural materials for aerospace systems.Acta Mater,2003,51(19):5775
[3]Starke Jr E A,Staley J T.Application of modern aluminum alloys to aircraft.Prog Aerosp Sci,1996,32(2-3):131
[4]Jia P F,Cao Y H,Geng Y D,et al.Effects of d.c.current on the phase transformation in 7050 alloy during homogenization.Mater Charact,2014,96:21
[5]Liu J,Kulak M.A new paradigm in the design of aluminum alloys for aerospace applications.Mater Sci Forum,2000,331-337:127
[6]Shu W X,Liu J C,Hou L G,et al.Microstructural evolution of Al--8.59Zn--2.00Mg-2.44Cu during homogenization.Int J Miner Metall Mater,2014,21(12):1215
[7]Li L,Deng Z Z,Han Y,et al.Study on cast and homogenized microstructure of a new super-high strength aluminum alloy.Light Alloy Fabric Technol,2011,39(12):20(李炼,邓桢桢,韩逸,等.新型超高强铝合金铸态及均匀化态组织研究.轻合金加工技术,2011,39(12):20)
[8]Robson J D.Microstructural evolution in aluminium alloy 7050during processing.Mater Sci Eng A,2004,382(1-2):112
[9]Yang X B,Chen J H,Liu J Z,et al.Spherical constituent particles formed by a multistage solution treatment in Al-Zn--Mg--Cu alloys.Mater Charact,2013,83:79
[10]Xiao T,Deng Y L,Ye L Y,et al.Effect of three-stage homogenization on mechanical properties and stress corrosion cracking of Al-Zn--Mg-Zr alloys.Mater Sci Eng A,2016,675:280
[11]Mahathaninwong N,Plookphol T,Wannasin J,et al.T6 heat treatment of rheocasting 7075 Al alloy.Mater Sci Eng A,2012,532:91
[12]Jia P F,Cao Y H,Geng Y D,et al.Studies on the microstructures and properties in phase transformation of homogenized 7050alloy.Mater Sci Eng A,2014,612:335
[13]Li J F,Peng Z W,Li C X,et al.Mechanical properties,corrosion behaviors and microstructures of 7075 aluminium alloy with various aging treatments.Trans Nonferrous Met Soc China,2008,18(4):755
[14]Liu Y,Jiang D M,Xie W L,et al.Solidification phases and their evolution during homogenization of a DC cast Al-8.35Zn-2.5Mg--2.25Cu alloy.Mater Charact,2014,93:173
[15]Wen K,Xiong B Q,Fan Y Q,et al.Transformation and dissolution of second phases during solution treatment of an Al--Zn-Mg--Cu alloy containing high zinc.Rare Met,2018,37(5):376
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