【作者】 尹向红；

【导师】 陈振华；

【作者基本信息】 湖南大学 ， 材料加工工程， 2006， 硕士

【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。更多还原

【Abstract】 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.更多还原