【作者】 段红玲；

【导师】 张丁非；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2008， 硕士

【摘要】 随着镁及其合金研究开发与制造技术水平的提高,镁合金的推广呈现高速增长态势,在交通工具、电子、军工等产品上获得越来越广泛的应用。由于镁合金是密排六方结构,滑移少,变形困难,所以镁合金的成形主要是压铸,传统的塑性加工的成形方式较少,但经过塑性加工之后,镁合金在组织性能上,将得到极大的改善。因此,探索和发展镁合金的塑性加工特性,研究适合于镁合金的塑性成形工艺具有非常重要的工程价值和学术意义。本文以自主开发的ZM61镁合金为研究对象,对其锭坯均匀化处理工艺和热变形行为进行研究。采用金相、扫面电镜及能谱和差热分析等手段,较为全面系统地研究了ZM61镁合金铸锭在不同均匀化热处理工艺条件下的显微组织和物相变化规律,并得到了在各种工艺条件下材料的显微硬度值随时间和温度的关系曲线,对均匀化的两个重要参数温度和时间进行了详细的探讨,并采用求显微硬度的方差大小的方法来判断热处理后合金的均匀化程度;通过扫描电镜实验,定性研究了ZM61镁合金中主要合金元素的分布规律。确定了ZM61镁合金较优的均匀化工艺参数为330℃×16h+420℃×2h。对ZM61镁合金采用较优的均匀化工艺处理后,在温度为300³90℃、应变速率为0.001⁰.1s-1的变形条件下,采用Gleele-1500热模拟机对其热压缩变形特性进行了研究。研究发现:ZM61镁合金热压缩变形时的流变应力同应变之间的关系曲线呈现典型的连续动态再结晶特征,即变形初期迅速硬化并达到一个峰值,其后逐渐软化,在达到较大的应变后呈现稳态流变。流态应力随变形温度的升高和变形速率的降低而降低。计算出ZM61镁合金热压缩变形时的材料常数为:Q=201.86kJ/mol;A=1.1915×10¹⁵s^-1;α=0.020756mm²/N;n=4.3159,并建立了合金的流变应力方程。同时也发现热压缩变形时,合金组织也发生了变化:变形程度增加,晶粒细化,动态再结晶进行的更加完全;温度升高促进动态再结晶进行完全;但是过高温度易使晶粒粗化;变形速率增大晶粒细化但动态再结晶的进行不完全。降低变形温度和提高应变速率可使再结晶晶粒平均尺寸减小,建立了再结晶晶粒大小d与Z参数之间关系模型为: d = 12788·Z^-2,12。综合考虑热压缩变形抗力、热压缩组织演化等因素,在本试验条件下,ZM61镁合金的较优加工工艺条件是:变形温度300³30℃,变形速率0.001～0.1s^-1,并以低速为宜。更多还原

【Abstract】 Along with the development of the research and manufacture, the magnesium alloys are used in many fields, just as vehicle, electronic products and military industry. Magnesium has hcp crystal structure and little slip system, so its plastic deformation is difficult. The main deformation of magnesium alloys is die-casting and traditional plastic processing is limitedly in magnesium. However, plastic processed magnesium alloys are highly improved in the microstructure and properties compared with die-casting products. So the development of plasticity procsseing is significant theoretical meaning and engineering value for the magnesium alloys.In this paper, ZM61 alloy studied by ourselves was chosen to investigate the homogenization and thermaldeformation. The variation of microstructure of ZM61 was discussed under different heat treatment with microscopic examination, SEM, EDS and DTA.Then we get the curve of micro hardness with temperature and time, also the parameter of heat process were carefully studied; Homogeneous level of alloy which had been treated was innovatively judged by the variance of micro hardness distribution; The regularities of distribution of alloying agent were analyzed to provide the attestation in secession by SEM. Final, the better uniformity of the process for ZM61 magnesium alloy is identified.Hot compression tests of ZM61 magnesium alloy after homogeneous annealing were performed on Gleeble-1500 at deformation temperature ranged in 300～390℃and strain rates 0.001～0.1s^-1. The results show that the stress and strain curve of ZM61 magnesium alloy has a typical feature of continuous dynamic recrystallization; first the flow stress rapidly emerged working hardening and reached a peak, then gradually softened and emerged steady-state flow when reached greater stain. The material constants of ZM61 magnesium alloy in the hot compressive deformation are calculated, Q=201.86kJ/mol;A=1.1915×1015s-1;α=0.020756mm2/N; n=4.3159, the flow stress equation was established. Meanwhile the microstructure is changed in the hot compressive deformation. The grain is refined and dynamic recrystallization is fully completed with increase of deformation. Dynamic recrystallization is accelerated with increase of temperature, but at the same time the grain is easy to grow coarse. The grain is refined with increase of the deformation rate, but dynamic recrystallization can’t be fully completed when the deformation rate is too high. The average dynamical recrystallized grian is decreased with reduction of deformation temperature and increase of strain rate. The equation of d and Z is established, d =12788·Z^-2,12.Tacking the factors such as resistance of compression, microstructure evolvement etc. it is considered that the good deformation condition is temperature of 300³30℃with strain rate 0.001～0.1s^-1 and the lower strain rate is preferred更多还原