大直径铝锭热顶铸造中超声施振深度的细晶机制
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摘要
在直径为650 mm的铝合金热顶半连续铸造过程中施加双源超声振动系统,研究3种超声辐射杆浸入深度对铸锭宏观凝固组织的影响.基于铝合金铸锭凝固组织形貌的检测结果以及ANSYS等有限元软件对铸造过程中声场的仿真结果,深入探讨了超声辐射杆在不同的施振深度下对铝合金铸锭凝固组织细化机制的影响.结果表明:随着超声辐射杆施振深度的增加,铸锭截面组织整体进一步细化,晶粒形状由发达的枝晶变为等轴枝晶;由于超声辐射杆端面以及柱面存在几个固定位置处振动波峰,在铝熔体中不同的超声施振深度下存在不同的超声空化范围,进而导致凝固组织的细化机制也不同.
With the development of the aerospace industry and the need for industrialized production,the casting processes of large diameter aluminum alloy ingot have come into focus in the industry. Among them,ultrasonic-assisted casting technology is widely used. Ultrasonic-assisted casting technology has the advantages of improving solute segregation of ingot and refining solidification organization. Other advantages have been widely reported. At present,most of the aluminum ingots used in the non-hot top ultrasonic casting process with very shallow liquid cavities,while the casting process does not involve the issue of ultrasonic vibration depth. With the use of a hot-top mold for ultrasound in the casting and casting process of large diameter ingot,the liquid level of aluminum melt is very high. The ultrasonic vibration depth will affect the cavitation range and finally affect the fine grain effect of the ingot. In the present study,a double source ultrasonic vibration system was applied in the process of semi-continuous casting of aluminum alloy with a diameter of 650 mm,and the influence of ultrasonic immersion depth on the macroscopic solidification structure of ingot was studied. Based on the test results of the solidified microstructure of aluminum alloy ingot and the simulation results of the sound field of the finite element software such as ANSYS,the mechanism of the microstructure refinement of the aluminum alloy ingot under different vibration depths was discussed at length. Study results show that,with increasing vibrational depth of the supersonic radiation rod,the whole cross section of the ingot is further refined,and grain shape changs from developed dendrites to equiaxed dendrites. Because of the endfaces of the ultrasonic radiation rod,there is a vibrational peak at the fixed position,which leads to different ultrasonic cavities under different ultrasonic vibrational depths in the aluminum melt. This leads to different refinement mechanisms of the solidified structure.
With the development of the aerospace industry and the need for industrialized production,the casting processes of large diameter aluminum alloy ingot have come into focus in the industry. Among them,ultrasonic-assisted casting technology is widely used. Ultrasonic-assisted casting technology has the advantages of improving solute segregation of ingot and refining solidification organization. Other advantages have been widely reported. At present,most of the aluminum ingots used in the non-hot top ultrasonic casting process with very shallow liquid cavities,while the casting process does not involve the issue of ultrasonic vibration depth. With the use of a hot-top mold for ultrasound in the casting and casting process of large diameter ingot,the liquid level of aluminum melt is very high. The ultrasonic vibration depth will affect the cavitation range and finally affect the fine grain effect of the ingot. In the present study,a double source ultrasonic vibration system was applied in the process of semi-continuous casting of aluminum alloy with a diameter of 650 mm,and the influence of ultrasonic immersion depth on the macroscopic solidification structure of ingot was studied. Based on the test results of the solidified microstructure of aluminum alloy ingot and the simulation results of the sound field of the finite element software such as ANSYS,the mechanism of the microstructure refinement of the aluminum alloy ingot under different vibration depths was discussed at length. Study results show that,with increasing vibrational depth of the supersonic radiation rod,the whole cross section of the ingot is further refined,and grain shape changs from developed dendrites to equiaxed dendrites. Because of the endfaces of the ultrasonic radiation rod,there is a vibrational peak at the fixed position,which leads to different ultrasonic cavities under different ultrasonic vibrational depths in the aluminum melt. This leads to different refinement mechanisms of the solidified structure.
引文
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[18] Dong F,Li X Q,Zhang L H,et al. Cavitation erosion mechanism of titanium alloy radiation rods in aluminum melt. Ultrason Sonochem,2016,31:150
[2] Moholkar V S,Rekveld S,Warmoeskerken M M C G. Modeling of the acoustic pressure fields and the distribution of the cavitation phenomena in a dual frequency sonic processor. Ultrasonics,2000,38(1-8):666
[3] Li X T,Li T J,Li X M,et al. Study of ultrasonic melt treatment on the quality of horizontal continuously cast Al-1%Si alloy. Ultrason Sonochem,2006,13(2):121
[4] Eskin G I. Effect of ultrasonic(cavitation)treatment of the melt on the microstructure evolution during solidification of aluminum alloy ingots. Z Metallkd,2002,93(6):502
[5] Komarov S V,Kuwabara M,Abramov O V. High power ultrasonic in pyrometallurgy:current status and recent development. ISIJ Int,2005,45(12):1765
[6] Chen D X,Li X Q,Li Z H,et al. Microstructure and macro-segregation law of ultrasonic cast 7050 aluminum alloy ingots. J Univ Sci Technol Beijing,2012,34(6):666(陈鼎欣,李晓谦,黎正华,等.超声铸造7050铝合金的微观组织和宏观偏析规律.北京科技大学学报,2012,34(6):666)
[7] Li Z H,Li X Q,Hu S C,et al. Effect of 7050 aluminum alloy melt treated by ultrasonic on macrosegregation in ingot. J Cent South Univ Sci Technol,2011,42(9):2669(黎正华,李晓谦,胡仕成,等.熔体超声处理对7050铝合金铸锭宏观偏析的影响.中南大学学报(自然科学版),2011,42(9):2669)
[8] Li R Q,Liu Z L,Dong F,et al. Grain refinement of a large-scale Al alloy casting by introducing the multiple ultrasonic generators during solidification. Metall Mater Trans A,2016,47(8):3790
[9] Tudela I,Sez V,Esclapez M D,et al. Simulation of the spatial distribution of the acoustic pressure in sonochemical reactors with numerical methods:a review. Ultrason Sonochem,2014,21(3):909
[10] Eskin G I. Broad prospects for commercial application of the ultrasonic(cavitation)melt treatment of light alloys. Ultrason Sonochem,2001,8(3):319
[11] Liu X B,Osawa Y,Takamori S,et al. Microstructure and mechanical properties of AZ91 alloy produced with ultrasonic vibration. Mater Sci Eng A,2008,487(1-2):120
[12] Eskin G I. Principles of ultrasonic treatment:application for light alloys melts. Adv Perform Mater,1997,4(2):223
[13] Nie M X. Cavitation prevention with roughened surface. J Hydraul Eng,2015,127(10):878
[14] Doyle W M. Aluminum alloys:structure and properties. Met Sci,1976,35(11):408
[15] Li X T,Zhao J Q,Ning S B,et al. Effect of high-intensity ultrasonic on the solidification of Al-1%Si alloy by horizontally continuous cast. Rare Met Mater Eng,2006,35(Suppl 2):284(李新涛,赵建强,宁绍斌,等.功率超声对水平连铸Al-1%Si合金凝固的影响.稀有金属材料与工程,2006,35(增刊2):284)
[16] Fan X M. Metal Solidification Theory and Technology. Wuhan:Wuhan University of Technology Press,2012(范晓明.金属凝固理论与技术.武汉:武汉理工大学出版社,2012)
[17] Xu T,Zhang L H,Li R Q,et al. Numerical simulation and experimental study of multi-field coupling for semi-continuous casting of large-scale aluminum ingots with ultrasonic treatment.Chin J Eng,2016,38(9):1270(徐婷,张立华,李瑞卿,等.铝合金大铸锭超声半连铸多场耦合的数值模拟与实验研究.工程科学学报,2016,38(9):1270)
[18] Dong F,Li X Q,Zhang L H,et al. Cavitation erosion mechanism of titanium alloy radiation rods in aluminum melt. Ultrason Sonochem,2016,31:150