电磁辅助钛合金激光沉积修复过程研究

发布时间：2018-03-07 19:04

本文选题：TA15钛合金　切入点：交变旋转磁场　出处：《沈阳航空航天大学》2017年硕士论文　论文类型：学位论文

【摘要】：电磁搅拌技术是通过导电液态金属切割磁感应线感生出洛伦兹力进行非接触式搅拌,作为一种有效的辅助制造手段,它在铸造、焊接、激光沉积制造等涉及金属熔池凝固的领域,用于提高成形质量,解决加工过程中出现的气孔和熔合不良等问题。在激光沉积制造领域,激光熔池“微小熔体”在激光热源的辐射下伴随着复杂的流体流动过程,施加磁场后其内部传能、传质行为更加复杂。为了能够更好的研究电磁搅拌辅助激光沉积修复过程中旋转磁场对TA15钛合金熔池内部影响及作用机制。首先,构建了一种三相三极旋转式电磁搅拌器作用下微小熔池内部的磁流体力学数学模型。运用该模型计算了不同激励电流情况下磁场中心处的磁感应强度和熔池内熔体周向流速。其次,采用有限体积法对施加磁场前后激光单道动态熔凝TA15钛合金过程进行三维磁-热耦合数值模拟,研究了磁场对激光熔池流场、熔凝单道及其周边基材温度分布、温度梯度分布以及固液界面处温度梯度和凝固速度,并结合柱状晶/等轴晶转变(CET)理论分析了电磁对凝固组织的影响。最后采用试验手段对上述模拟结果及分析计算所得趋势进行了验证。结果表明,电磁力驱使熔体作周向运动,且随着远离磁场中心,洛伦兹力越大,周向流速越大。随着激励电流的增大,磁感应强度增强,熔质周向流速增大。电磁搅拌作用下的旋转磁场使得激光熔池最大流速增加了约20%,对流加剧促进了熔池热交换作用使其最高温度下降,固液分界面处温度梯度大幅降低,凝固速度小幅增大,从而有利于熔池顶部组织发生CET转变。试验结果显示电磁搅拌器对熔质产生一个周向力,该力促使熔质流动加剧并作周向流动,同时促使熔凝层顶部有等轴晶组织生成,且随着远离磁场中心,电磁力增大,等轴晶区有扩大趋势,此结果与计算分析结果的分析趋势相吻合。
[Abstract]:Electromagnetic stirring technology is to produce Lorentz force by cutting the magnetic induction line of liquid metal to produce non-contact stirring. As an effective auxiliary manufacturing method, it is casting and welding. Laser deposition manufacturing and other fields related to solidification of metal melting pool are used to improve the forming quality and solve the problems of bad porosity and fusion in the process of processing. Under the radiation of laser heat source, the "micro melt" in the laser melting pool is accompanied by a complicated fluid flow process, and the internal energy is transmitted after the application of a magnetic field. Mass transfer behavior is more complicated. In order to study the effect and mechanism of rotating magnetic field on the molten pool of TA15 titanium alloy in the process of electromagnetic agitation assisted laser deposition, In this paper, a mathematical model of magnetohydrodynamics in the micro-pool under the action of a three-phase three-pole rotating electromagnetic agitator is constructed. The magnetic induction intensity at the center of the magnetic field and the melting in the molten pool are calculated by using the model under different excitation currents. Body circumferential velocity. Second, Three-dimensional magneto-thermal coupling numerical simulation of laser single channel dynamic melting of TA15 titanium alloy before and after the application of magnetic field was carried out by finite volume method. The temperature distribution of laser melting pool, single channel and its surrounding substrate was studied by magnetic field. Temperature gradient distribution, temperature gradient and solidification velocity at solid-liquid interface, Combined with columnar crystal / equiaxed crystal transition (CET) theory, the effect of electromagnetism on solidification microstructure was analyzed. Finally, the simulation results and the calculated trends were verified by means of experiments. The results show that the electromagnetic force drives the melt to move in a circumferential direction. As the magnetic field is far away from the center of the magnetic field, the greater the Lorentz force is, the greater the circumferential velocity is. With the increase of the excitation current, the intensity of the magnetic induction increases. The rotating magnetic field under electromagnetic stirring increases the maximum flow velocity of the laser molten pool by about 20. The convection accelerates the heat exchange in the molten pool to decrease the maximum temperature, and the temperature gradient at the solid-liquid interface decreases significantly. The results show that the electromagnetic agitator produces a circumferential force on the melt, which makes the flux increase and flow circumferentially. At the same time, the equiaxed crystal structure is formed at the top of the melting layer, and the electromagnetic force increases with the distance from the center of the magnetic field, and the equiaxed crystal region tends to expand, which is consistent with the analytical trend of the calculated results.
【学位授予单位】：沈阳航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

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