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A new approach to control centerline macrosegregation in Al-Mg-Si alloys during twin roll continuous casting
Accepted Manuscript A new approach to control centerline macrosegregation in Al-Mg-Si alloys during twin roll continuous casting K.M Sun, L Li, S.D Chen, G.M Xu, G Chen, R.D.K. Misra, G Zhang PII: DOI: Reference:
S0167-577X(16)31993-0 http://dx.doi.org/10.1016/j.matlet.2016.12.109 MLBLUE 21921
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
9 September 2016 16 November 2016 28 December 2016
Please cite this article as: K.M Sun, L. Li, S.D Chen, G.M Xu, G. Chen, R.D.K. Misra, G. Zhang, A new approach to control centerline macrosegregation in Al-Mg-Si alloys during twin roll continuous casting, Materials Letters (2016), doi: http://dx.doi.org/10.1016/j.matlet.2016.12.109
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A new approach to control centerline macrosegregation in Al-Mg-Si alloys during twin roll continuous casting K.M Sun1,2,L Li1, S.D Chen2 , G.M Xu1,2,*, G Chen1 , R.D.K. Misra3 , G Zhang1 1. Key Laboratory of Electromagnetic Processing of Materials of Ministry of Education, Northeastern University, Shenyang 110819, China 2. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China 3. Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso 79912, USA
Abstract Al-1.0%Mg-1.2%Si sheets were processed by twin-roll casting process under static magnetic field, pulse electric current field and combined fields. The evolution of centerline macro-segregation in each processing condition was studied. The study suggests that the application of combined static magnetic field and pulse electric current field are more effective in controlling the macrosegregation during twin-roll casting process as compared to in the presence of a single physical field is used. Additionally, the effect of single pulse electric current field was greater than the single static magnetic field with regard to macrosegregation. Keywords: macrosegregation; pulse electric field; static magnetic field; twin roll casting
1. Introduction Twin-roll strip casting (TRC) is one of the most potential technologies for metallurgical industry in the 21st century [1]. Advantage of this process is based on combining cast and hot rolling into a single operation to produce thin strips with thickness of 3~10 mm directly from the molten metal [2]. Compared with the conventional processes, TRC decreased the technological processing time, reduces production cost, energy and waste. However, centerline macrosegregation is a challenge in TRC [3]. This defect strongly influences the microstructure and mechanical properties, reduces the fatigue strength, and even causes localized porosities or cracks [4]. Hence, control of centerline macrosegregation during TRC process is an aspect of significance. The rolling parameters to eliminate macrosegregation in aluminum alloys strips have been studied for decades [5] [6] and [7]. But the subject remains unclear and new approaches are required to mitigate centerline macrosegregation. In the convectional direct chill (DC) casting, macro segregation is also a problem. To overcome the defect, external physical fields are applied to the DC casting processes, such as low frequency electromagnetic field [8], alternating [9] and direct electromagnetic field [10], electric current pulse [11] [12] and ultrasonic field [13]. The experimental results indicated that these approaches are more or less effective to reduce or eliminate macrosegregation in DC casting. Based on this, it is of potential interest to apply physical fields in the TRC process, which may effectively help eliminate the macro segregation. However, the experiments have not been reported.
2. Materials and methods We have studied the effects of a single weak static magnetic field (SMF), a single pulse
electric current field (PECF) and the combination of SMF and PECF on macrosegregation of various elements in the TRC sheets. The experimental device mainly consisted of SMF and EPCF generators, resistance furnace, rolls with cooling facilities, mill pulpit, nozzle and sluice. The Al-1.0%Mg-1.2%Si alloy was selected as the study material. The alloy was melted in resistance furnace and held at 720 for 1 h. Before pouring, degassing and removing slag, and pouring at 690 to casting channel, then into the casting nozzle and hereinafter into the rolling gap, where the material solidifies quickly and is partially deformed. During the roll casting, the single PECF, the single SMF and their combined fields were respectively applied to the forming process. The process parameters are presented in Table 1. Optical microscope (OM), scanning electron microscope (SEM) and electro-probe micro analyzer (EPMA) were used to analyze the experimental results.
3. Results and discussion Fig. 1 shows optical images of segregation of alloying elements in four sheets. Black ribbon-like A and white zone B was found in the sample in conventional twin roll casting process. EPMA analyses reveal that the ribbon-like in the center is contained by 3.32% Mg, 6.15% Si, 0.83% Fe, and balance Al. The white zone was 0.82% Mg, 0.94% Si, and balance Al. The contact of alloying element in ribbon-like was far greater than the bulk chemical component. In other words, significant segregation occurred near the centerline of the sheet. In addition, it was found that Fe element mainly present in the centerline. Fig. 2 shows the distribution tendency of Mg and Si in α(Al) matrix from the edge to the center of sheets further, where fluctuations of Mg and Si with combined SMF and PECF were more placid than the other conditions. The results are consistent with the optical micrograph. It is well known, macrosegregation is directly related to the solidification process. When solidification advances from the surface of two rolls towards the hotter part of the casting, the driving force (the difference in free energy between the solid phase and liquid phase ) leads to solute to enrich in the solidification front, until segregation occurs near the kiss-point (Fig. 3c). When SMF was applied to melt, a resistance can be formed, also referred as magnetic braking force, which is generated by the melt cutting the magnetic induction line. Liu in 2006 [14] showed that SMF can decrease the velocity of flow, meanwhile, depresses reflux in the cast-rolling zone. Such, instead of reducing segregation, it increased centerline segregation in the sheet. When an alternating pulse electric current I was applied to the twin roll casting process, a Lorentz force F1 was generated as shown as Fig. 3a, which is simulated by Maxwell. The F1 is composed of magnetic pressure and magnetic pull. When the pulsed electric current I increases, the magnetic pressure is dominant. In contrary, with current transition, the magnetic pressure transforms into magnetic pull. When I is intermittment, the F1 is magnetic pressure at the edge of solidified layer, while magnetic pull occurs in the center of melt [15]. The magnitude of F1 in the semi-solid zone is 10-100 N/m3. Considering Fig. 1b, it is obvious that F1 is not adequately large to eliminate the solutes segregation. Instead, the solute migrates a relatively short distance by F1 as shown in Fig. 3d. In addition, when PECF and SMF are simultaneously applied to twin roll casting, it can generate one of the most important action, F2=J× ×B , Where J is the density of pulse electric current, B is the magnetic induction that is perpendicular to pulse electric current, and B is the volume electromagnetic force.
The size of F2 in Fig. 3b in the mushy zone is about 100 times more than the force that is generated by a single PECF or SMF. Therefore, F1 and magnetic braking force are ignored in the combined physical fields. F2 consists of magnetic pressure and magnetic pull. When F2 acts on solutes, the relatively long movement occurred in interdendritic channels, as shown as Fig. 3e. Simultaneously, F2 will drive the melt with forced convection, which causes partially solidified dendritic re-melting. These broken dendrites are driven to the two-phase region, new crystals are nucleated and solidification is completed at a higher cooling, which results in a fine grained structure in the center. Chu and Jacoby [16] suggested that these fine dendrites are depleted of solute, and are responsible for negative centerline segregation. this also explains why external combined physical fields are beneficial in reducing segregation in the TRC process.
4. Conclusions The external physical fields lead a significant effect on centerline segregation in twin roll casting process. They mainly influenced the centerline segregation through the electromagnetic force impacting solute migration. The application of combined fields was more effective in controlling centerline macrosegregation of sheets formation in TRC as compared to individually applied field. References 1.
J.K. Brimacombe. Metall. Mater. Trans.: B 30 (1999) 553–556.
2.
Hu Zhao, Peijie Li, Liangju He. J. MATER PROCESS TECH. 211 (2011) 1197-1202.
3.
Y. Birol. J. Aluminium 74 (1998) 553–556.
4.
Zheng Lv, Fengshan Du, Zhongjian An, Huagui Huang, Zhiqiang Xu, Jingna Sun. J ALLOY COMPD. 643 (2015) 270–274.
5.
Yucel Birol. J ALLOY COMPD. 486 (2009) 168-172.
6.
Hongbin Wang, Le Zhou, Yongwen Zhang, Yuanhua Cai, Jishan Zhang. J. MATER PROCESS TECH. 233 (2016) 186-191.
7.
Yun-Soo Lee, Hyoung-Wook Kim, Jae-Hyung Cho. Procedia Engineering. 81 (2014) 1547-1552.
8.
Chen Dandan, Zhang Haitao, Wang Xiangjie, Cui Jiangzhong. ACTA METALLURGICA SINICA. 47 (2011) 185-190.
9.
Lei Li, Qingfeng Zhu, Zhihao Zhao, Haitao Zhang, Yubo Zuo, Jianzhou Cui. J. Mater. Res. 30 (2015) 745-752.
10. J.L. Meyer, J. Szekely, N. Elkaddah, C. Vives, R. Ricou. Metall. Trans. 29 (1987) 18. 11. Xi-bin Li, Feng-gui Lu, Hai-Chao Cui, Xin-hua Tang. Trans. Nonferrous Met. Soc. China. 24 (2014) 192-198. 12. Hongxiang Jiang, Jiuzhou Zhao, Cuiping Wang, Xingjun Liu. Mater Lett. 132 (2014) 66-69. 13. Dinesh Kumar Koli, Geeta Agnihotri, Rajesh Purohit. Mater Today. 2 (2015) 3017-3026. 14. Liu yong. Numerical Simulation on Electromagnetic Cast-rolling Process of Twin-roll Magnesium Alloys Strip. M.E. Northeastern University. 2006. 15. Li yingju, Feng xiaohui, Yang yuansheng. C-MRS. 2011. 16. Chu MG, Jacoby JE. In: Bickert CM, editor. Light metals. Earrendale [PA]: TMS; 1990. P. 925-30.
Acknowledgements The authors are grateful to Jinlan Group Guangdong of China (No. 2013B090600015), aluminium Co. Guangdong of China (No. 2014B090903012 and No. 2013B090200008 ) and the China Postdoctoral Science Foundation (No. 2015M570250) for financial support.
Table 1.
The parameters of twin roll casting
The parameters of twin roll casting Thickness of two rolls
Value 5 mm
Speed of rolls
0.8 m·min-1
Diameter of two rolls
500 mm
The frequency, peak current and duty cycle of PECF
20 HZ, 300 A and 0.15
The magnetic flux density of SMF
24 mT
Fig .1. Macrosegregation of alloying elements in the TRC process (a) conventional TRC process (b) with PECF (c) with SMF (d) with combined PECF and SMF. The yellow lines show the line scan paths; the red circle and the rectangular show elements rich areas; A point and B point are selected as delegate of the black and the white zone to confirm and analyze percent composition of the alloys
elements .
Fig. 2. Distribution of Mg and Si elements from the edge to the center of sheets during different processing
Fig. 3. Schematic diagram of mechanism involved in the TRC process with PECF or combined physical fields, (a) distribution of pulse electromagnetic force F1, (b) distribution of combined electromagnetic force F 2, (c) forming mechanism of alloying segregation in the TRC process (d) acting mechanism of F1 on the alloying solute (e) acting mechanism of F2 on the alloying solute
1. sheets are manufactured by twin-roll casting with different physical fields; 2. Effect of different physical fields on macro-segregation of sheets was researched; 3. The centerline segregation in sheets was eliminated by combined fields; 4. Action mechanism of physical field on centerline segregation was analyzed.
S0167-577X(16)31993-0 http://dx.doi.org/10.1016/j.matlet.2016.12.109 MLBLUE 21921
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
9 September 2016 16 November 2016 28 December 2016
Please cite this article as: K.M Sun, L. Li, S.D Chen, G.M Xu, G. Chen, R.D.K. Misra, G. Zhang, A new approach to control centerline macrosegregation in Al-Mg-Si alloys during twin roll continuous casting, Materials Letters (2016), doi: http://dx.doi.org/10.1016/j.matlet.2016.12.109
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A new approach to control centerline macrosegregation in Al-Mg-Si alloys during twin roll continuous casting K.M Sun1,2,L Li1, S.D Chen2 , G.M Xu1,2,*, G Chen1 , R.D.K. Misra3 , G Zhang1 1. Key Laboratory of Electromagnetic Processing of Materials of Ministry of Education, Northeastern University, Shenyang 110819, China 2. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China 3. Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso 79912, USA
Abstract Al-1.0%Mg-1.2%Si sheets were processed by twin-roll casting process under static magnetic field, pulse electric current field and combined fields. The evolution of centerline macro-segregation in each processing condition was studied. The study suggests that the application of combined static magnetic field and pulse electric current field are more effective in controlling the macrosegregation during twin-roll casting process as compared to in the presence of a single physical field is used. Additionally, the effect of single pulse electric current field was greater than the single static magnetic field with regard to macrosegregation. Keywords: macrosegregation; pulse electric field; static magnetic field; twin roll casting
1. Introduction Twin-roll strip casting (TRC) is one of the most potential technologies for metallurgical industry in the 21st century [1]. Advantage of this process is based on combining cast and hot rolling into a single operation to produce thin strips with thickness of 3~10 mm directly from the molten metal [2]. Compared with the conventional processes, TRC decreased the technological processing time, reduces production cost, energy and waste. However, centerline macrosegregation is a challenge in TRC [3]. This defect strongly influences the microstructure and mechanical properties, reduces the fatigue strength, and even causes localized porosities or cracks [4]. Hence, control of centerline macrosegregation during TRC process is an aspect of significance. The rolling parameters to eliminate macrosegregation in aluminum alloys strips have been studied for decades [5] [6] and [7]. But the subject remains unclear and new approaches are required to mitigate centerline macrosegregation. In the convectional direct chill (DC) casting, macro segregation is also a problem. To overcome the defect, external physical fields are applied to the DC casting processes, such as low frequency electromagnetic field [8], alternating [9] and direct electromagnetic field [10], electric current pulse [11] [12] and ultrasonic field [13]. The experimental results indicated that these approaches are more or less effective to reduce or eliminate macrosegregation in DC casting. Based on this, it is of potential interest to apply physical fields in the TRC process, which may effectively help eliminate the macro segregation. However, the experiments have not been reported.
2. Materials and methods We have studied the effects of a single weak static magnetic field (SMF), a single pulse
electric current field (PECF) and the combination of SMF and PECF on macrosegregation of various elements in the TRC sheets. The experimental device mainly consisted of SMF and EPCF generators, resistance furnace, rolls with cooling facilities, mill pulpit, nozzle and sluice. The Al-1.0%Mg-1.2%Si alloy was selected as the study material. The alloy was melted in resistance furnace and held at 720 for 1 h. Before pouring, degassing and removing slag, and pouring at 690 to casting channel, then into the casting nozzle and hereinafter into the rolling gap, where the material solidifies quickly and is partially deformed. During the roll casting, the single PECF, the single SMF and their combined fields were respectively applied to the forming process. The process parameters are presented in Table 1. Optical microscope (OM), scanning electron microscope (SEM) and electro-probe micro analyzer (EPMA) were used to analyze the experimental results.
3. Results and discussion Fig. 1 shows optical images of segregation of alloying elements in four sheets. Black ribbon-like A and white zone B was found in the sample in conventional twin roll casting process. EPMA analyses reveal that the ribbon-like in the center is contained by 3.32% Mg, 6.15% Si, 0.83% Fe, and balance Al. The white zone was 0.82% Mg, 0.94% Si, and balance Al. The contact of alloying element in ribbon-like was far greater than the bulk chemical component. In other words, significant segregation occurred near the centerline of the sheet. In addition, it was found that Fe element mainly present in the centerline. Fig. 2 shows the distribution tendency of Mg and Si in α(Al) matrix from the edge to the center of sheets further, where fluctuations of Mg and Si with combined SMF and PECF were more placid than the other conditions. The results are consistent with the optical micrograph. It is well known, macrosegregation is directly related to the solidification process. When solidification advances from the surface of two rolls towards the hotter part of the casting, the driving force (the difference in free energy between the solid phase and liquid phase ) leads to solute to enrich in the solidification front, until segregation occurs near the kiss-point (Fig. 3c). When SMF was applied to melt, a resistance can be formed, also referred as magnetic braking force, which is generated by the melt cutting the magnetic induction line. Liu in 2006 [14] showed that SMF can decrease the velocity of flow, meanwhile, depresses reflux in the cast-rolling zone. Such, instead of reducing segregation, it increased centerline segregation in the sheet. When an alternating pulse electric current I was applied to the twin roll casting process, a Lorentz force F1 was generated as shown as Fig. 3a, which is simulated by Maxwell. The F1 is composed of magnetic pressure and magnetic pull. When the pulsed electric current I increases, the magnetic pressure is dominant. In contrary, with current transition, the magnetic pressure transforms into magnetic pull. When I is intermittment, the F1 is magnetic pressure at the edge of solidified layer, while magnetic pull occurs in the center of melt [15]. The magnitude of F1 in the semi-solid zone is 10-100 N/m3. Considering Fig. 1b, it is obvious that F1 is not adequately large to eliminate the solutes segregation. Instead, the solute migrates a relatively short distance by F1 as shown in Fig. 3d. In addition, when PECF and SMF are simultaneously applied to twin roll casting, it can generate one of the most important action, F2=J× ×B , Where J is the density of pulse electric current, B is the magnetic induction that is perpendicular to pulse electric current, and B is the volume electromagnetic force.
The size of F2 in Fig. 3b in the mushy zone is about 100 times more than the force that is generated by a single PECF or SMF. Therefore, F1 and magnetic braking force are ignored in the combined physical fields. F2 consists of magnetic pressure and magnetic pull. When F2 acts on solutes, the relatively long movement occurred in interdendritic channels, as shown as Fig. 3e. Simultaneously, F2 will drive the melt with forced convection, which causes partially solidified dendritic re-melting. These broken dendrites are driven to the two-phase region, new crystals are nucleated and solidification is completed at a higher cooling, which results in a fine grained structure in the center. Chu and Jacoby [16] suggested that these fine dendrites are depleted of solute, and are responsible for negative centerline segregation. this also explains why external combined physical fields are beneficial in reducing segregation in the TRC process.
4. Conclusions The external physical fields lead a significant effect on centerline segregation in twin roll casting process. They mainly influenced the centerline segregation through the electromagnetic force impacting solute migration. The application of combined fields was more effective in controlling centerline macrosegregation of sheets formation in TRC as compared to individually applied field. References 1.
J.K. Brimacombe. Metall. Mater. Trans.: B 30 (1999) 553–556.
2.
Hu Zhao, Peijie Li, Liangju He. J. MATER PROCESS TECH. 211 (2011) 1197-1202.
3.
Y. Birol. J. Aluminium 74 (1998) 553–556.
4.
Zheng Lv, Fengshan Du, Zhongjian An, Huagui Huang, Zhiqiang Xu, Jingna Sun. J ALLOY COMPD. 643 (2015) 270–274.
5.
Yucel Birol. J ALLOY COMPD. 486 (2009) 168-172.
6.
Hongbin Wang, Le Zhou, Yongwen Zhang, Yuanhua Cai, Jishan Zhang. J. MATER PROCESS TECH. 233 (2016) 186-191.
7.
Yun-Soo Lee, Hyoung-Wook Kim, Jae-Hyung Cho. Procedia Engineering. 81 (2014) 1547-1552.
8.
Chen Dandan, Zhang Haitao, Wang Xiangjie, Cui Jiangzhong. ACTA METALLURGICA SINICA. 47 (2011) 185-190.
9.
Lei Li, Qingfeng Zhu, Zhihao Zhao, Haitao Zhang, Yubo Zuo, Jianzhou Cui. J. Mater. Res. 30 (2015) 745-752.
10. J.L. Meyer, J. Szekely, N. Elkaddah, C. Vives, R. Ricou. Metall. Trans. 29 (1987) 18. 11. Xi-bin Li, Feng-gui Lu, Hai-Chao Cui, Xin-hua Tang. Trans. Nonferrous Met. Soc. China. 24 (2014) 192-198. 12. Hongxiang Jiang, Jiuzhou Zhao, Cuiping Wang, Xingjun Liu. Mater Lett. 132 (2014) 66-69. 13. Dinesh Kumar Koli, Geeta Agnihotri, Rajesh Purohit. Mater Today. 2 (2015) 3017-3026. 14. Liu yong. Numerical Simulation on Electromagnetic Cast-rolling Process of Twin-roll Magnesium Alloys Strip. M.E. Northeastern University. 2006. 15. Li yingju, Feng xiaohui, Yang yuansheng. C-MRS. 2011. 16. Chu MG, Jacoby JE. In: Bickert CM, editor. Light metals. Earrendale [PA]: TMS; 1990. P. 925-30.
Acknowledgements The authors are grateful to Jinlan Group Guangdong of China (No. 2013B090600015), aluminium Co. Guangdong of China (No. 2014B090903012 and No. 2013B090200008 ) and the China Postdoctoral Science Foundation (No. 2015M570250) for financial support.
Table 1.
The parameters of twin roll casting
The parameters of twin roll casting Thickness of two rolls
Value 5 mm
Speed of rolls
0.8 m·min-1
Diameter of two rolls
500 mm
The frequency, peak current and duty cycle of PECF
20 HZ, 300 A and 0.15
The magnetic flux density of SMF
24 mT
Fig .1. Macrosegregation of alloying elements in the TRC process (a) conventional TRC process (b) with PECF (c) with SMF (d) with combined PECF and SMF. The yellow lines show the line scan paths; the red circle and the rectangular show elements rich areas; A point and B point are selected as delegate of the black and the white zone to confirm and analyze percent composition of the alloys
elements .
Fig. 2. Distribution of Mg and Si elements from the edge to the center of sheets during different processing
Fig. 3. Schematic diagram of mechanism involved in the TRC process with PECF or combined physical fields, (a) distribution of pulse electromagnetic force F1, (b) distribution of combined electromagnetic force F 2, (c) forming mechanism of alloying segregation in the TRC process (d) acting mechanism of F1 on the alloying solute (e) acting mechanism of F2 on the alloying solute
1. sheets are manufactured by twin-roll casting with different physical fields; 2. Effect of different physical fields on macro-segregation of sheets was researched; 3. The centerline segregation in sheets was eliminated by combined fields; 4. Action mechanism of physical field on centerline segregation was analyzed.