【作者】 吴远军；

【导师】 李春峰；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2011， 硕士

【摘要】 磁脉冲成形的变形速率为准静态成形的100-1000倍。能显著提高金属的成形能力,同时,可使材料从微观组织到力学性能产生一系列的改变。因此本文从数值模拟、工艺实验、微观组织分析三个方面,对纯Cu棒、Q235板在脉冲磁场力驱动下的冲击变形和晶粒细化等内容进行了研究。利用DEFORM-3D得到了圆棒磁脉冲高速镦粗和平板磁脉冲高速冲击的载荷-行程曲线,并分析了平板磁脉冲高速冲击后板材的等效应变分布规律。结果表明,每次变形过程中,板材弯曲延伸区和未变形区会产生协调变形,等效应变在板长方向分布不均匀,导致板材的左右两端会产生约1个齿宽的“畸变区”,在板中间有小幅波动,波动幅度随着压制道次的增加而变大。冲击变形试样的显微组织观察表明,圆棒磁脉冲高速镦粗和平板磁脉冲高速冲击方法都有效细化了材料的晶粒。在圆棒磁脉冲高速镦粗条件下,纯Cu棒由原始的200μm细化为大量微米级细晶和拥有微米级亚结构的粗晶;在平板磁脉冲高速冲击条件下,Q235板平均晶粒尺寸由20.7μm细化为5.15μm。硬度分析结果表明,在本文研究条件下,纯Cu试样的加工硬化现象不显著,但心部硬度高于其他部位。Q235板A区和B区的硬度都随着道次的增加而上升,在第1道次时上升幅度最大,经过4道次变形后,A区与B区硬度差异消失; A区和B区的I.F.值先增大后减小,表明加工硬化不均匀性在第1道次时上升最大,而后逐渐减小。进行了平板磁脉冲高速冲击与CGP的比较研究,结果表明,平板磁脉冲高速冲击能够延缓裂纹的产生,变形更均匀,增加板材的可压制道次;平板磁脉冲高速冲击细化晶粒能力更强,相同道次下,细化速率更快,板材晶粒弯曲的现象不明显;平板磁脉冲高速冲击下的硬度要低;平板磁脉冲高速冲击下条件下板材A区和B区的I.F.值要比CGP的要小,因此平板磁脉冲高速冲击改善了材料的加工硬化均匀性。更多还原

【Abstract】 The deformation rate of magnetic pulse forming is 100-1000 times as that of the Quasi-static forming, and magnetic pulse forming can expand the forming limit of metallic materials effectively and lead to a series of improvements in materials’mechanical properties and microstructure. In this paper, the punching deformation and the refining process of pure Cu and Q235 steel under the magnetic pulse forming process are studied from the aspects of simulation, test and microstructure analysis.The load-stroke Curves of high-speed upsetting of magnetic pulse and high-speed impact of magnetic pulse are obtained by DEFORM-3D. The effective strain of Q235 plate’s high-speed impact of magnetic pulse is analyzed and 3 different strain parts are found. Firstly both the Curved and extended areas and the unreformed parts have a compatible deformation during the deformation process; secondly, the distribution of effective strain in the plate is relatively well-proportioned in the direction of thickness and width orientation while it is seriously uneven in the length direction, whereas, there is a distorted area with the width of one tooth in the right and left end of the plate respectively. Thirdly, the fluctuation of effective strain in the length direction becomes greater with the increase of pressing numbers.Based on metallographic observation, the laws of grain refinement of high-speed upsetting of magnetic pulse and high-speed impact of magnetic pulse are obtained in this paper. Under Electromagnetic high-speed upsetting, the pure Cu is ultimately subdivided into a large number of submicron grains and coarse-grains with sub-micron structures. Under high-speed impact of magnetic pulse, Q235 steel refines the average grain size from 20.7μm to 5.15μm. Based on the observation, the hardness of Cu bar in vertical section and in horizontal section will increase as the pressure increases, but the change is small. The phenomenon indicates the hardness improved little and the central section is harder than other areas. Under high-speed impact of magnetic pulse, the average hardness of section A and section B will increase with the upsetting times increasing. The maximum augment happened in the 1st term. Although the initial hardness of the section A and section B are different, after four terms, both sections could achieve the same hardness at last. However, the non-uniformity of hardness in section B is more serious than that in section A.Based on the comparison of the High-speed impact of magnetic pulse and the constrained groove pressing, the following results is obtained: 1) high-speed impact of magnetic pulse can delay the cracks as the number of upsetting times increases. And under the same condition, the high-speed impact of magnetic pulse’s deformation is more uniform.2) the high-speed impact of magnetic pulse elucidates the stronger refinement ability and higher refining rate. Meanwhile grains’bending phenomenon is not obvious. The angle of the direction of the grain and the board will be smaller .3) In the 1st deformation term, the hardness of the sheet under two methods will rapidly increase, but under high-speed impact of magnetic pulse are greater and surprisingly get a lower final hardness value.4) under high-speed impact of magnetic pulse the I.F. values of section A and section B are smaller than those under constrained groove pressing, so the high-speed impact method can improve material’s hardness uniformity.更多还原