【作者】 孙景刚；

【导师】 刘政军；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2009， 博士

【摘要】 随着工业技术的迅速发展和机械化、自动化程度的不断提高，对机械设备和零件磨损引起的危害越来越被人们重视，减少磨料磨损与提高机械使用寿命具有很大的经济意义。电磁作用焊接技术是近年来完善起来的一种新的焊接技术，应用也同趋广泛。根据外加间歇交变磁场粉末等离子弧堆焊焊接过程的非线性、多因素、非稳念、强耦合的特点，综合运用电磁学、磁性物理、焊接冶金等多种交叉学科的知识，运用非电量检测技术和有限元数值分析等方法建立了外加间歇交变磁场粉末等离子弧堆焊磁场的数学模型并进行了模拟仿真。建立了外加间歇交变磁场粉木等离子弧堆焊焊接过程中外加磁场及其分布的通用数学分析模型，采用有限元法计算了不同焊接条件下外加间歇交变磁场及其分布，分析了不同间歇交变磁场参数对外加间歇交变磁场及其分布的影响规律。其模拟结果与实际测量结果具有良好的一致趋势，从而验证了间歇交变磁场及其分布数值分析的模型是准确的，具有一定的通用性。外加纵向间歇交变磁场促使电弧旋转，改变等离子弧柱等离子流和电流密度的径向分布，影响母材的加热熔化和焊缝成形。外加横向间歇交变磁场改变了电弧的摆动频率。实践表明，利用外加磁场对焊接中熔滴的过渡、熔池金属的流动、熔池的结晶形核及结晶生长等过程有显著作用，使堆焊层的一次结晶组织细化，控制硬质相的分布，减小化学不均匀性，从而提高了堆焊层金属的硬度和耐磨性，全面改善堆焊层的性能。在等离子弧堆焊铁基、镍基合金粉末时外加纵向和横向间歇交变磁场，研究了外加间歇交变磁场对堆焊层组织的影响规律，系统地考察了不同磁场种类与堆焊层金属性能和微观组织之间的关系，着重叙述了外加间歇交变磁场对堆焊层金属凝固过程的作用机理，揭示了堆焊层中硬质相的形态分布，并做出了理论分析和研究探讨，得到以下主要结果：1、在适当的间歇交变磁场参数(励磁电流、磁场频率、磁场占空比)匹配作用下，堆焊层组织才能获得最佳的细化效果。2、没有施加磁场时，硬质相杂乱无章的分布;在最佳的问歇交变磁场参数作用下，堆焊层中硬质相细小且均匀分布，此时堆焊层金属的硬度和磨损量均达到最佳状态。3、由实验的结果可知：纵向间歇交变磁场作用下当磁场电流I_磁=3A、f=10Hz及μ=50％时，铁基堆焊层金属的硬度为HRC68，磨损量△G=0.0318g。纵向间歇交变磁场作用下当磁场电流I_磁=3A、f=10Hz及μ=50％时，镍基堆焊层金属的硬度为HRC52.4，磨损量△G=0.39g;横向间歇交变磁场作用下当磁场电流I_磁=3A、f=10Hz及μ=50％时，堆焊层金属性能达到最佳值，此时硬度HRC67.7，磨损量△G=0.0323g。横向间歇交变磁场作用下当磁场电流I_磁=3A、f=10Hz及μ=50％时，镍堆焊层金属性能达到最佳值，此时硬度HRC51.7，磨损量△G=0.42g。更多还原

【Abstract】 With the rapid development of industry technology and continued increase of the degree of mechanization and automation, people pay more attention to hazard of parts wearing. It has a great economic significance that decrease grinding abrasion and increase mechanical wearing.Electromagnetic technology is applied to welding as a new welding method in recent years. The numerical analysis models of intermittent alternative magnetic field and its distribution are established at first time, and general control equation and boundary condition are presented, according to the characteristics of nonlinear, multi-factor, transient and strong coupling in the intermittent alternative magnetic field, by using non-electric quantity measuring techniques and finite-element analysis method. The general numerical simulation models of intermittent alternative magnetic field of plasma arc surfacing layer are constructed for the first time, which is suitable for calculating the distribution of intermittent alternative magnetic field. The models of distribution of intermittent alternative magnetic field have been validated by carrying out welding technology tests comprehensively. It is shown that the computed results are found to be in good agreement with the experimentally observed one or the precise analysis result.The applied intermittent alternative longitudinal magnetic field promotes arc revolution, changes plasma jet of arc column and radial distribution of density of arc, affects the heating and melting of base metal and formation of weld. The intermittent alternative transverse magnetic field has influence on the swing frequency of welding arc.Experience shows that the introduced magnetic field can give an effective intervention to the transition of droplet, flowing of molten bath metal, crystalline and nucleation of molten bath and the process of crystalline growth. The magnetic field promotes the refining degree of primary crystallization structure , decreases the chemistry non-homogeneity, So it can strengthen hardness and wearing resistance of weld metal overlay and improve quality of surfacing deposit.This paper talks about plasma arc surfacing Fe-based alloy powder, Ni-based alloy powder alloy powder on low carbon steel with applied intermittent alternative magnetic field. The effect of the intermittent alternative magnetic field on the surfacing deposit solidification structure and mechanical properties is studied and the relationship of different magnetic field types and material wearing resistance has been examined systematically. The mechanism for overlay welding metal during solidification by applied intermittent alternative magnetic field has been discussed intentionally. It shows the shape and distribution of hard phase in overlay welding, and makes theoretical analysis and preliminary discussion. Following are the main results:1、The optimum parameters( the current of magnetic field, the frequency of magnetic field and the duty ratio of magnetic field) of intermittent alternative magnetic field can greatly influence grain structure refinement in plasma overlay.2、The hard phase in weld metal overlay is distributed randomly without magnetic field;With the using intermittent alternative magnetic field, the hard phase in weld metal overlay is fine and distributed "the hexagon" in optimum parameters, then hardness and wear extent in weld metal overlay are higher.3、The result indicated: with the effect of intermittent alternative longitudinal magnetic field, when the optimum magnetic field electric current is 3A, magnetic field frequency is 10Hz and magnetic field duty ratio is 50%, hardness in Fe-based overlay is HRC68, wear loss△G=0.0318g. with the effect of intermittent alternative longitudinal magnetic field, when the optimum magnetic field electric current is 3A, magnetic field frequency is 10Hz and magnetic field duty ratio is 50%, hardness in Ni-based overlay is HRC52.4, wear loss△G=0.39g; with the effect of intermittent alternative transverse magnetic field, when the optimum magnetic field current is 3A, magnetic field frequency is10Hz and magnetic field duty ratio is 50%, hardness of Fe-based overlay is HRC67.7, wear loss△G=0.0323g. with the effect of intermittent alternative transverse magnetic field, when the optimum magnetic field current is 3A, magnetic field frequency is10Hz and magnetic field duty ratio is 50%, hardness of Ni-based overlay is HRC51.7, wear loss△G=0.42g.更多还原