镁合金型材挤压模具设计与工艺研究
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摘要
镁合金由于具有密度低、比强度和比模量高、减震和抗电磁辐射等优点，在航空、航天、交通运输、电子、电器等领域具有广阔的应用前景。但迄今为止，对具有复杂断面的镁合金型材挤压技术的研究尚处于起步阶段。
本论文设计了镁合金平面分流挤压模具，成功地制备出了AZ31、AZ91和ZK60等多型号、多规格型材，较系统地研究了镁合金铸锭的固溶处理工艺、挤压工艺参数对镁合金挤压成形性能和挤压制品组织性能的影响规律。论文的主要研究内容和得到的结果如下：
1．以汽车用镁合金型材为研究对象，根据镁合金的挤压变形特点，对模具的分流比、分流桥、模芯、焊合室、工作带和分流孔的形状、大小和分布等平面分流挤压模设计要素进行了系统的分析。在此基础上，设计了三套断面形状分别为“日”、“目”和“田”字形的平面分流挤压模。挤压模的主要结构参数为：4孔扇形对称的分流方式和水滴形分流桥，模芯工作带长度为10.3mm，焊合室高度为16mm，分流比分别为8.06、9.55、8.11。实验结果表明，所设计的模具完全适用于复杂截面镁合金薄壁型材的挤压成形。
2．镁合金铸锭的组织对挤压成形性能的影响非常显著。为此本论文对AZ31、AZ91和ZK60铸锭的固溶处理艺进行了较系统的研究，通过金相分析等手段探讨和分析了固溶处理温度和时间对铸锭微观组织的影响规律，研究结果表明：在固溶处理过程中镁合金铸锭显微组织发生了明显的变化，随着固溶温度的升高和固溶时间的延长，铸造组织中的枝晶偏析消除，粗大析出相的数量减少、形态由片状变为点状、分布由连续网状变为随机弥散分布。对AZ91和ZK60合金铸锭而言，比较理想的固溶处理工艺参数分别为460℃、10～15h和480℃、15h，可保证析出相充分溶解而基体合金的晶粒组织又不致于过分粗化长大，对改善合金的挤压成形能力十分有利。
3．研究了挤压温度、挤压速度、挤压比等工艺参数对复杂截面镁合金型材成形性能的影响规律，挤压工艺参数对型材组织性能的影响规律和挤压过程中的焊合特点。实验结果表明：挤压温度和速度是是影响镁合金挤压成形性能的关键工艺参数，AZ91和ZK60合金型材的合适挤压温度分别为380℃和340℃左右，挤压速度为3～5mm/s，此时型材表面光滑且焊合良好。挤压温度过高或过低、速度过快时均易引起开裂。随着挤压速度的升高，型材晶粒组织粗化。镁合金型材的室温力学性能随挤压比的增大而提高。挤压比为36．7的AZ31和ZK60“田”字形型材的室温抗拉强度和断裂伸长率分别可达239MPa，14.3％和297MPa，17.1％。两种镁合金的室温拉伸断口均呈准解理断裂。
Wrought Mg alloys have found wide application in transportation,aerospace, aerospace vehicle, 3C products, etc., due to its excellent mechanicalproperties and physical properties, including low density, high specific strength,high specific modulus, electromagnetic radiation absorption, etc. But fewerreports on the extrusion modes of Mg alloys products with complexcross-section.
In this thesis, plain divergent extrusion modulus for Mg alloys weredesigned; wrought AZ31, AZ91 and ZK60 sectional bars were extruded. Thesolid solution processing and its influences combined with extrusion processingvariables on the formability, the microstructures and mechanical properties ofthe as-extruded alloy. The main content and experimental results are drawn asfollows;
1．The Mg alloy hollow sections for automotive was selected as studyobject. According to the deformation properties of the Mg alloys duringextrusion, the designing elements, including diversion ratio, diversion bridge,seaming room, modulus core and its working band, and the shape, size anddistribution of the divergent orifices, etc. were systematically analyzed. Theresets of plain divergent extrusion dies with“日”、“目”and“田”cross-section weredesigned. The main structural parameters of the dies include 4 fanning divergentorifices symmetrically distributed, teardrop bridge, the working band of the diecore of 10．3mm, the height of the seaming room of 16mm, the diversion ratiosof 8．06, 9．55 and 8．11 respectively. The experimental results that the as-designeddies are proper for production of thin wall wrought Mg alloy sections.
2．The solid solution treatment processing of AZ31, AZ91 and Zk60 alloyingots were investigated. The influences of solid solution temperature andholding time on the microstructures of the ingots were examined. Theexperimental results show that high temperature and long holding time canobviously reduce dendrite segregation and coarse precipitates. The shape of theprecipitates change from network to dispersoid which can improve theworkability of Mg alloy ingots. The optimized temperature and time for AZ91and ZK60 alloy ingots in this study are 460℃, 10～15h and 480℃, 15h,respectively.
3．The effects of extrusion temperature, extrusion speed, extrusion ratio, etc. on the formability of the ingot and the microstructures of the as-extrudedsections were investigated. The seaming features in the sections were examined.The experimental results show that the extrusion temperature and extrusionspeed are the two key variables for Mg alloys. The two optimized parameters forAZ91 and ZK60 alloy are 380℃, 3～5mm/s and 340℃, 3～5mm/s, respectively.Higher or lower temperature easily leads to cracking during extruding. Higherextrusion speed can also lead to coarse grains in the sections. On the other hand,larger extrusion ratios can lead to higher room temperature mechanicalproperties. The tensile strength and fracture elongation of AZ31 and ZK60 alloysections of with“田”cross-section extruded at extrusion ratio of 36．7 are239MPa, 14．3% and 297MPa, 17．1% respectively. The fracture mechanisms ofthe two alloy samples during tensile are quasi-cleavage cracking.
本论文设计了镁合金平面分流挤压模具，成功地制备出了AZ31、AZ91和ZK60等多型号、多规格型材，较系统地研究了镁合金铸锭的固溶处理工艺、挤压工艺参数对镁合金挤压成形性能和挤压制品组织性能的影响规律。论文的主要研究内容和得到的结果如下：
1．以汽车用镁合金型材为研究对象，根据镁合金的挤压变形特点，对模具的分流比、分流桥、模芯、焊合室、工作带和分流孔的形状、大小和分布等平面分流挤压模设计要素进行了系统的分析。在此基础上，设计了三套断面形状分别为“日”、“目”和“田”字形的平面分流挤压模。挤压模的主要结构参数为：4孔扇形对称的分流方式和水滴形分流桥，模芯工作带长度为10.3mm，焊合室高度为16mm，分流比分别为8.06、9.55、8.11。实验结果表明，所设计的模具完全适用于复杂截面镁合金薄壁型材的挤压成形。
2．镁合金铸锭的组织对挤压成形性能的影响非常显著。为此本论文对AZ31、AZ91和ZK60铸锭的固溶处理艺进行了较系统的研究，通过金相分析等手段探讨和分析了固溶处理温度和时间对铸锭微观组织的影响规律，研究结果表明：在固溶处理过程中镁合金铸锭显微组织发生了明显的变化，随着固溶温度的升高和固溶时间的延长，铸造组织中的枝晶偏析消除，粗大析出相的数量减少、形态由片状变为点状、分布由连续网状变为随机弥散分布。对AZ91和ZK60合金铸锭而言，比较理想的固溶处理工艺参数分别为460℃、10～15h和480℃、15h，可保证析出相充分溶解而基体合金的晶粒组织又不致于过分粗化长大，对改善合金的挤压成形能力十分有利。
3．研究了挤压温度、挤压速度、挤压比等工艺参数对复杂截面镁合金型材成形性能的影响规律，挤压工艺参数对型材组织性能的影响规律和挤压过程中的焊合特点。实验结果表明：挤压温度和速度是是影响镁合金挤压成形性能的关键工艺参数，AZ91和ZK60合金型材的合适挤压温度分别为380℃和340℃左右，挤压速度为3～5mm/s，此时型材表面光滑且焊合良好。挤压温度过高或过低、速度过快时均易引起开裂。随着挤压速度的升高，型材晶粒组织粗化。镁合金型材的室温力学性能随挤压比的增大而提高。挤压比为36．7的AZ31和ZK60“田”字形型材的室温抗拉强度和断裂伸长率分别可达239MPa，14.3％和297MPa，17.1％。两种镁合金的室温拉伸断口均呈准解理断裂。
Wrought Mg alloys have found wide application in transportation,aerospace, aerospace vehicle, 3C products, etc., due to its excellent mechanicalproperties and physical properties, including low density, high specific strength,high specific modulus, electromagnetic radiation absorption, etc. But fewerreports on the extrusion modes of Mg alloys products with complexcross-section.
In this thesis, plain divergent extrusion modulus for Mg alloys weredesigned; wrought AZ31, AZ91 and ZK60 sectional bars were extruded. Thesolid solution processing and its influences combined with extrusion processingvariables on the formability, the microstructures and mechanical properties ofthe as-extruded alloy. The main content and experimental results are drawn asfollows;
1．The Mg alloy hollow sections for automotive was selected as studyobject. According to the deformation properties of the Mg alloys duringextrusion, the designing elements, including diversion ratio, diversion bridge,seaming room, modulus core and its working band, and the shape, size anddistribution of the divergent orifices, etc. were systematically analyzed. Theresets of plain divergent extrusion dies with“日”、“目”and“田”cross-section weredesigned. The main structural parameters of the dies include 4 fanning divergentorifices symmetrically distributed, teardrop bridge, the working band of the diecore of 10．3mm, the height of the seaming room of 16mm, the diversion ratiosof 8．06, 9．55 and 8．11 respectively. The experimental results that the as-designeddies are proper for production of thin wall wrought Mg alloy sections.
2．The solid solution treatment processing of AZ31, AZ91 and Zk60 alloyingots were investigated. The influences of solid solution temperature andholding time on the microstructures of the ingots were examined. Theexperimental results show that high temperature and long holding time canobviously reduce dendrite segregation and coarse precipitates. The shape of theprecipitates change from network to dispersoid which can improve theworkability of Mg alloy ingots. The optimized temperature and time for AZ91and ZK60 alloy ingots in this study are 460℃, 10～15h and 480℃, 15h,respectively.
3．The effects of extrusion temperature, extrusion speed, extrusion ratio, etc. on the formability of the ingot and the microstructures of the as-extrudedsections were investigated. The seaming features in the sections were examined.The experimental results show that the extrusion temperature and extrusionspeed are the two key variables for Mg alloys. The two optimized parameters forAZ91 and ZK60 alloy are 380℃, 3～5mm/s and 340℃, 3～5mm/s, respectively.Higher or lower temperature easily leads to cracking during extruding. Higherextrusion speed can also lead to coarse grains in the sections. On the other hand,larger extrusion ratios can lead to higher room temperature mechanicalproperties. The tensile strength and fracture elongation of AZ31 and ZK60 alloysections of with“田”cross-section extruded at extrusion ratio of 36．7 are239MPa, 14．3% and 297MPa, 17．1% respectively. The fracture mechanisms ofthe two alloy samples during tensile are quasi-cleavage cracking.
引文
[1]陈振华等编著．镁合金[M]．北京：化工出版社，2004
[2]李窘等，Mg合金研究现状及其应用[J]．金属材料研究，2003(3)：24-31
[3]刘正，张奎，曾小勤著，镁基轻质合金理论基础及应用[M]．北京：机械工业出版社，2002
[4]Kojima Y. Platform science and technology for advanced magnesium alloys[J]. Materials Science Forum, 2000: 350-351, 3
[5]刘庆踞，刘勇兵，杨晓红．镁合金的研究及其在汽车工业中的应用与展望[J]．汽车工程，2002(2)：94-100
[6]田素贵，郭华，单智伟，等．AZ31Mg合金的高温蠕变及相关因数[J]．材料热处理学报，2001(增刊)：78
[7]Bussiba A, Ben A A, et al. Grain Refinement of AZ31 and ZK60 Magnesium Alloy-towards Superplasticity Studies[J]. Mater Sci Eng, 2001, A302:56
[8]刘静安，铝型材挤压模具设计、制造、使用及维修．北京：冶金工业出版社．2002
[9]丁文江，王渠东，刘满平．轻金属技术的进展[M]．．北京：科学技术出版社，2002
[10]Hiroyoki W. Superplasticity in a ZK60 magnesium alloy at low temperatures[J], Scripta Materialia, 1999, 40(22): 477-484
[11]常国成，王建中．金属凝固过程的晶体产生与控制[M]．北京：冶金工业出版社)
[12]中国机械工程学会铸造专业学会编．铸造手册．第三卷．铸造非铁合金[M]．北京：机械工业出版社，1999．166-219
[13]波尔特诺伊，列别杰夫A A著，林裴译．镁合金手册(工艺与性质)[M]．北京：冶金工业出版社，1959，3-398
[14]Michael M A, Hugh Baker. ASM Specialty Handbook Magnesium and Magnesium Alloys[M]. Ohio: ASM International, 1999
[15]中国南方航空动力机械公司冶金技术文件．铸造镁合金熔炼操作说明书，通用S501-016
[16]付珍．轻型金属镁的发展及应用[J]．山西机械，2003(3)：8-10．
[17]张文周、姚素娟．用镁棒和镁合金棒的生产[J]，世界有色金属，2003(8)：18-20
[18]王忠堂，张士宏，许沂，等．镁合金管材挤压工艺及力能参数实验研究[J]，沈阳工业大学学报，2001，20(4)：66-69
[19]Ruden T J, Albright D L. High ductility magnesium alloys in automotive application[J].Advanced Master & Process, 1999,145(6):28-32
[20]翟秋亚．基于SIMA法的AZ91镁合金半固态组织演变[硕士学位论文]，西安理工大学，2003
[21]Roger A P. Light Metals,1990,837-843
[22]张青来，卢晨，丁文江．分流挤压镁合金管材工艺研究[J]．轻合金加工技术，2004，6：28-30
[23]翟秋亚，王智民，袁森等．挤压变形对AZ31镁合金组织和性能的影响[J]．西安理工大学学报，2004，5：254-258
[24]洪深泽．挤压工艺及模具设计[M]．机械工业出版社，1996，199-200
[25]李海江．镁合金挤压成形工艺数值模拟的研究[D]，华中科技大学硕士论文，2003
[26]Frederick P S,Bradly N I,Erickson S C.Injection molding magnesium alloys[J].Advance Materials & Processes,1988,134:53-56
[27]Mwembela A, Konopleva E B,Mcqueen H J. Microstructural development in Mg Alloy AZ31 during hot working[J].Sripta Materialia, 1997,37
[28]Prasad Y V, Seshacharyulu T. Modelling of hot deformation for microstructure control[J].International Materials Reviews, 1998,43:243-258
[29]Maeng D Y, Kim T S,Lee J H,etal. Microstructure and strength of rapidly solidification and extruded Mg-Zn alloys[J].Scripta Mater,2000,43:385-389
[30]张小明．铝合金挤压技术及在镁合金加工中的应用[J]．稀有金属快板2002，(7)：18—19
[31]Edward M, Mielnik. Metalworking Science and Engineering[M].McGraw-Hill.Inc. 1991
[32]Liu Yi.Superplasticity and Microstructureal. Evolution Mechanical Engineering Congress and Exposition Orlando,Florida,2000,275-279
[33]Kim W, Chung S W, Kum D. Superplasticity in Thin Magnesium Alloy sheet and Deformation Mechanism Maps for Magnesium Alloys at Elevated Temperatures[J].Acta Matu,2001,(49):3337-3345
[34]Hatta N, Takuda H,Yoshii T.Finitc Element Analysis of the Formability of a Magnesiumbased Alloy AZ31 Sheet[J]. Journal of Processing Technology,1999,(89): 135-140
[35]Droder k,Doege E.sheet Metal Forming of Magnesium Wrought Alloys-Formability and Process Technology[J],Joural of Materials Technology,2001 ,(115): 14-19
[2]李窘等，Mg合金研究现状及其应用[J]．金属材料研究，2003(3)：24-31
[3]刘正，张奎，曾小勤著，镁基轻质合金理论基础及应用[M]．北京：机械工业出版社，2002
[4]Kojima Y. Platform science and technology for advanced magnesium alloys[J]. Materials Science Forum, 2000: 350-351, 3
[5]刘庆踞，刘勇兵，杨晓红．镁合金的研究及其在汽车工业中的应用与展望[J]．汽车工程，2002(2)：94-100
[6]田素贵，郭华，单智伟，等．AZ31Mg合金的高温蠕变及相关因数[J]．材料热处理学报，2001(增刊)：78
[7]Bussiba A, Ben A A, et al. Grain Refinement of AZ31 and ZK60 Magnesium Alloy-towards Superplasticity Studies[J]. Mater Sci Eng, 2001, A302:56
[8]刘静安，铝型材挤压模具设计、制造、使用及维修．北京：冶金工业出版社．2002
[9]丁文江，王渠东，刘满平．轻金属技术的进展[M]．．北京：科学技术出版社，2002
[10]Hiroyoki W. Superplasticity in a ZK60 magnesium alloy at low temperatures[J], Scripta Materialia, 1999, 40(22): 477-484
[11]常国成，王建中．金属凝固过程的晶体产生与控制[M]．北京：冶金工业出版社)
[12]中国机械工程学会铸造专业学会编．铸造手册．第三卷．铸造非铁合金[M]．北京：机械工业出版社，1999．166-219
[13]波尔特诺伊，列别杰夫A A著，林裴译．镁合金手册(工艺与性质)[M]．北京：冶金工业出版社，1959，3-398
[14]Michael M A, Hugh Baker. ASM Specialty Handbook Magnesium and Magnesium Alloys[M]. Ohio: ASM International, 1999
[15]中国南方航空动力机械公司冶金技术文件．铸造镁合金熔炼操作说明书，通用S501-016
[16]付珍．轻型金属镁的发展及应用[J]．山西机械，2003(3)：8-10．
[17]张文周、姚素娟．用镁棒和镁合金棒的生产[J]，世界有色金属，2003(8)：18-20
[18]王忠堂，张士宏，许沂，等．镁合金管材挤压工艺及力能参数实验研究[J]，沈阳工业大学学报，2001，20(4)：66-69
[19]Ruden T J, Albright D L. High ductility magnesium alloys in automotive application[J].Advanced Master & Process, 1999,145(6):28-32
[20]翟秋亚．基于SIMA法的AZ91镁合金半固态组织演变[硕士学位论文]，西安理工大学，2003
[21]Roger A P. Light Metals,1990,837-843
[22]张青来，卢晨，丁文江．分流挤压镁合金管材工艺研究[J]．轻合金加工技术，2004，6：28-30
[23]翟秋亚，王智民，袁森等．挤压变形对AZ31镁合金组织和性能的影响[J]．西安理工大学学报，2004，5：254-258
[24]洪深泽．挤压工艺及模具设计[M]．机械工业出版社，1996，199-200
[25]李海江．镁合金挤压成形工艺数值模拟的研究[D]，华中科技大学硕士论文，2003
[26]Frederick P S,Bradly N I,Erickson S C.Injection molding magnesium alloys[J].Advance Materials & Processes,1988,134:53-56
[27]Mwembela A, Konopleva E B,Mcqueen H J. Microstructural development in Mg Alloy AZ31 during hot working[J].Sripta Materialia, 1997,37
[28]Prasad Y V, Seshacharyulu T. Modelling of hot deformation for microstructure control[J].International Materials Reviews, 1998,43:243-258
[29]Maeng D Y, Kim T S,Lee J H,etal. Microstructure and strength of rapidly solidification and extruded Mg-Zn alloys[J].Scripta Mater,2000,43:385-389
[30]张小明．铝合金挤压技术及在镁合金加工中的应用[J]．稀有金属快板2002，(7)：18—19
[31]Edward M, Mielnik. Metalworking Science and Engineering[M].McGraw-Hill.Inc. 1991
[32]Liu Yi.Superplasticity and Microstructureal. Evolution Mechanical Engineering Congress and Exposition Orlando,Florida,2000,275-279
[33]Kim W, Chung S W, Kum D. Superplasticity in Thin Magnesium Alloy sheet and Deformation Mechanism Maps for Magnesium Alloys at Elevated Temperatures[J].Acta Matu,2001,(49):3337-3345
[34]Hatta N, Takuda H,Yoshii T.Finitc Element Analysis of the Formability of a Magnesiumbased Alloy AZ31 Sheet[J]. Journal of Processing Technology,1999,(89): 135-140
[35]Droder k,Doege E.sheet Metal Forming of Magnesium Wrought Alloys-Formability and Process Technology[J],Joural of Materials Technology,2001 ,(115): 14-19