【作者】 陈强；

【导师】 罗守靖；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2006， 硕士

【摘要】 MB15-RE属于高强度镁合金,在航天领域有着广泛应用。目前,镁合金的成形方法有压铸、锻造和挤压等。然而,压铸方法不能保证结构件的力学性能要求;锻造、挤压方法不能满足形状复杂结构件的形状要求。半固态金属加工是一种新发展的一次近净成形复杂形状制件技术,其制件力学性能接近锻件,其制件形状复杂程度接近压铸件。半固态金属加工技术的出现为镁合金复杂结构件成形开辟了一条新路。在镁合金半固态成形中,制备半固态镁合金非枝晶组织和获得半固态镁合金触变成形的最佳工艺是关键。基于此,本文研究了三种不同状态MB15-RE镁合金(铸态、等径道角挤压态和液相线模锻态)触变组织的生成及其特征、在高固相率下等温压缩过程中的力学行为和流变特性。本文以实验室制备的三种不同状态(铸态、等径道角挤压态和液相线模锻态)MB15-RE镁合金为原材料,采用等温热处理法分别制备了具有半固态非枝晶组织的坯料。借助光学显微镜研究了它们重熔后的组织。结果表明,三种不同状态的MB15-RE镁合金在等温热处理过程中都能形成非枝晶的半固态球状组织;随着加热温度的提高或保温时间的延长,晶粒形状变得更加圆整;与液相线模锻态和铸态MB15-RE镁合金相比,ECAE态镁合金在半固态温度下可获得更细小、更圆整的球状组织。通过半固态等温压缩实验,研究了在高固相率下三种不同状态的MB15-RE镁合金在半固态下的力学行为。结果表明,三种不同状态合金的真应力—真应变曲线都具有三个阶段:应力上升阶段、应力下降阶段和应力稳定阶段;三种状态的镁合金的峰值应力随着应变速率的增大而升高,而稳态应力随着应变速率的增大而下降;在相同应变速率下,铸态镁合金的峰值应力和稳态应力都随加热温度的升高而降低;当加热温度、应变速率和保温时间一定时,ECAE态合金的峰值应力和稳态应力分别都比铸态和液相线模锻态的峰值应力和稳态应力低;当加热温度、应变速率一定时,随着保温时间的延长,ECAE态镁合金的峰值应力和稳态应力先下降后上升。利用三种不同状态合金在高固相率下的稳态应力和相关公式分别得到了表观粘度随不同参数(固相率、剪切速率、晶粒大小和保温时间)的变化曲线。结果表明,铸态镁合金的表观粘度随着固相率的减小而降低;三种不同状态的镁合金在半固态下的表观粘度随着剪切速率的增大而降低;在固相更多还原

【Abstract】 MB15-RE, which belongs to high strength magnesium alloy, has been widely used in the field of astronavigation. At present, forming technologies of magnesium alloys include die-casting, forging and extrusion, and so on. However, the mechanical properties of magnesium alloy can’t be satisfied by means of die casting technology. As for forging and extrusion, they can’t satisfy the shape requirement of work piece with complex shape. Semi-solid metal processing is a new net-shape forming technology, in which complex shape close to cast parts and high mechanical properties close to forge piece can be obtained. The arrival of Semi-solid metal forging has established a new way for magnesium alloy work pieces with complex shape. Generally speaking, preparing non-dendritic structure in Semi-solid state and obtaining the best thixotropic process parameters are key factors for Semi-solid metal processing. Based on this, by means of three different kinds MB15-RE magnesium alloy (as-cast,as-ECAEed and as-liquidus forged)prepared by experimental methods, the formation and the character of thixo-structure, mechanical behavior and rheological characteristic of MB15-RE magnesium alloy with high solid fraction have been investigated in this paper.In this study, Semi-solid isothermal heat treatment is employed to prepare the non-dendritic structure in Semi-solid state for three different kinds’billets. In addition, with the help of optical microscope, their partial remelting microstructures are also studied. The results demonstrate that non-dendritic structures in Semi-solid state of three different kinds billets have been obtained; the higher the temperature is or the longer the holding time is, the smoother the boundary of grains turn; in comparison with those of as-cast and as-liquidus forged MB15-RE magnesium alloy, as-ECAEed MB15-RE magnesium alloy can get the smaller and the smoother spheroidized structure.The experiment of Semi-solid state isothermal compression is employed to investigate the mechanical behavior of three kind’s billets in semi-solid state with high solid fraction. From the results obtained it can be concluded that the true stress-true strain curves of three states are characterized by three stages, those are更多还原