【作者】 郑顺奇；

【导师】 张治民；

【作者基本信息】 中北大学 ， 机械设计及理论， 2013， 博士

【摘要】 轮毂作为车辆主要承力构件,同时也是高速转动构件,使用镁合金实现其轻量化,将取得较大的节能减排效果,具有十分重要实用价值。目前,镁合金轮毂设计处于半经验和半理论状态,缺乏可靠的设计准则。以铸造工艺为主的镁合金轮毂,轮辐力学性能低,性能均一性和稳定性差；而镁合金锻造工艺能够提高其力学性能高,满足轮毂使用要求,但是镁合金变形能力差,成形困难；锻造成形轮毂工序多,成形效率低,制造成本高。因此,急需开发一种镁合金轮毂结构科学的设计方法和成形技术。因此,本文针对镁合金轮毂现状,开展镁合金轮毂模态分析与铸-挤复合成形技术研究,通过性能测试分析和成形验证,研究开发一种镁合金轮毂结构设计方法和新的成形理论和技术。首先,通过镁合金轮毂模态与受力特征仿真分析,提出一种采用模态分析和等效静力韧度相等相结合的设计准则,进行了轮毂结构优化设计。以约化强度、等效静力韧度为选材依据,进行了材料选用研究,并确定AZ91D镁合金为轮毂制造材料。其次,通过热/力模拟实验,基于动态材料模型建立了AZ91D镁合金的二维加工图,确定了较为合理的变形温度和应变速率。研究了镁合金压缩动态再结晶过程,建立了AZ91D镁合金发生动态再结晶临界应力模型,并通过平面应变压缩试验,研究了AZ91D镁合金成形组织和力学性能响应,为镁合金构件组织和性能控制成形提供参考。第三,借助于数值仿真技术,研究了AZ91D镁合金低压铸造成形过程缺陷形成规律,在此基础上,优化了低压铸造模型和工艺参数,为镁合金低压铸造成形的工艺参数制定和模具设计提供参考。以形变均匀性因子为评价指标,着重研究了变形温度、变形程度和变形速度参数和坯料结构参数对变形均匀性影响,建立了形变均匀性因子和变形“三度”工艺参数、结构参数之间的关系模型,为镁合金构件成形坯料结构设计和均匀变形控制提供理论依据。本文首次提出镁合金轮毂铸件,采用局部变形改性的铸-挤复合成形方法,性能达到使用要求,提高了生产效率和材料利用率,降低了生产成本。建立了形变均匀性因子、变形“三度”工艺参数和结构参数之间的关系模型,实现了镁合金构件均匀变形控制成形,保证了成形构件性能的均一性和稳定性。最后,设计制造各工序的成形工装,进行了AZ91D镁合金轮毂铸-挤压复合成形验证试验。成功试制出性能满足使用要求的镁合金轮毂,实验证明以模态分析为基础,采用等效静力韧度相等的设计准则,较传统的半经验半理论设计方法更加科学合理。为镁合金轮毂铸—挤复合成形技术的工程化应用奠定基础。更多还原

【Abstract】 Wheels are main load-bearing and high-speed rotating components.It is very important significance for saving energy and reduction emission, using magnesium alloy to manufacture wheels with light weight. The design methods for magnesium alloy wheel are in the state of half experience and half theory,and are not reliable criteria for wheels designs.Casting is main forming technology for magnesium alloy wheels.and the casting properities is poor.It is difficult to guarantee the performance uniformity and stability by casting.The mechnical properities of forged magnesium alloy are perfect for wheels. But because of bad deformation ability,it is difficulty for forging.There are need many processes for wheels foging and the forming efficiency is low. It also is difficulty to reduce the costs. So, the new design methold and forming technology are need urgently for magnesium alloy wheels.Aiming at the deficiency design method、low peroperities of casting spoke、bad peroperities of uniformity and reliablty of casting technology and low efficiency and many processes of forging technology for magnesium alloy wheel forming. the present study researched on the modal analysis and casting-extrusion compound forming technology for magnesium alloy wheels.On the base of results of the forming verification testingand and properities testing,studied the new design methold and forming Principle and technology.for magnesium alloy wheels.Firstly, the results of the dynamic/static characteristics studing of magnesium alloy wheels using numerical simulation technology are references foe materials selection and the structures optimization. The basies of reduction strength and equivalent static toughness were used for mateiral selection. The AZ91D magnisium alloy was selected as wheels manufacturing material. Optimized the structure of wheel by using design criteria by using modal analysis and equivalent static toughness matching. The results of materials and structure parameters are reference for magnesium alloy wheels forming by casting-extrusion technology.Secondly, based on dynamic material model, this trail-manufacture experiment established a two-demensional processing map of AZ91D magnesium alloy using the thermal and force simulation experiment. The processing map are the reference for parameters selection. Studied the process of dynamic recrystallizatin during compression and established the dynamic recrystallization critical stress model of AZ91D. Studied the forming microstructures and mechanical properties response by plane strain compression tests. Providing the reference for microstructures and microstructures and mechanical properties controlling for magnesium components.Thirdly, the rule of defects formation of AZ91D was studied during process of low pressure casting by numerical simulation technology.The results of optimized parameters of low pressure casting model and process were the reference for dies dedsigning and forming process parameters selection. Using deformation homogeneity factor as evaluation index, studied effect on the deformation uniformity by deformation temperature、deformation velocity、deformation amount and structure factor. The model of relationship between deformation homogeneity factor an deformation temperature、deformation velocity、 deformation amount and structure factor was extablished. Providing the reference for billet structure desiging and deformation uniformity controlling for magnesium alloy components forming.The prent put forward method of lacation plastic deformation to improve the properties of the casting components for using, enhancing production efficiency and material utilization, reducing the production costs.The structure of magnesium alloy wheel was optimized using design criteria of modal analysisand matching equivalent static toughness. Compared with the traditional semi-empirical and emi-theory design methold, the prent methold is more scientific and reasonable. Established the model of relationship between deformation homogeneity factor an deformation temperature、deformation velocity、deformation amount and structure factor. Using the model, the billet strcture design became moe scientific.The magnesium alloy components forming became easier to be controlled. The formed structure mechanical properities uniformity and stability can be guaranteed. Put forward csting-extrusion compound technology for magnesium ally wheels,solved the problem of traditional forming process, improved the production efficiency, reduced the manufacturing cost of magnesium alloy wheels.At last, Designed the forming devices and studied the verification test for AZ91D magnesium alloy wheelusingcasting-extrusion compound thchnology.the properities of formed wheelare welland laid the foundation for engineering applications for magnesium alloy wheel using casting-extrusion compound forming technology.更多还原