【作者】 张宁；

【导师】 张松； 张春华；

【作者基本信息】 沈阳工业大学 ， 材料学， 2007， 硕士

【摘要】 铝合金由于密度小、塑性好、耐腐蚀性能优异、易于加工成形等特点被广泛应用于各个领域。但由于其存在强度低、耐磨性差的缺陷，限制了其应用范围。激光熔覆技术可显著提高材料表面的综合性能，目前，在激光熔覆工艺的实施过程中主要通过试验和经验来确定激光加工工艺参数，铝合金激光熔覆过程温度场数值模拟，对激光辐照工艺参数的选择和优化具有重要的意义。本文采用2kW连续波Nd：YAG激光加工系统，在6061铝合金表面激光熔覆SiC_p／Al金属基复合材料，运用有限元法，对激光熔覆过程的温度场进行了数值模拟和试验验证。在模拟计算过程中材料热物性随温度变化而改变，属于材料非线性问题；选用高斯函数分布的热源模型，通过APDL二次开发语言实现移动热源的加载和卸载；建立了激光熔覆瞬态温度分布数学模型，并划分了合适的网格，解决了熔覆热源移动的数学模拟问题。通过改变单元属性的方法，解决材料的熔化、凝固问题。分析了激光加工工艺参数对温度场的影响，系统地论述了激光熔覆过程的有限元分析理论，并结合数值计算的方法，对熔覆过程中产生的温度场进行了实时动态模拟研究，提出了基于ANSYS软件为平台的激光熔覆温度场的模拟分析方法。采用扫描电子显微镜和X射线衍射仪对6061铝合金表面SiC_p／Al激光熔覆层的组织、结构进行了分析检测，并针对具体的模拟结果进行了试验验证。本文建立的三维激光熔覆温度场的动态模拟分析方法，为优化铝合金激光熔覆工艺参数，提供了理论依据和指导。研究表明：激光辐照工艺参数决定了试样表面峰值温度以及温度梯度的分布，激光熔覆过程中熔池中心温度与激光扫描速度、光斑半径成反比，与激光功率成正比。激光扫描速度对熔池内的温度梯度影响较小，而激光输出功率及光斑半径则对熔池内温度梯度影响较大。模拟结果与验证试验基本吻合，6061铝合金表面激光熔覆SiC_p／Al复合涂层的最佳工艺参数为：激光输出功率1200W，扫描速度5mm／s，激光辐照光斑半径1.25mm。更多还原

【Abstract】 Due to the advantages of light density, good plasticity, superior corrosion resistance,easy workability etc, aluminum alloys are widely applied to variety fields. But because of itsdefects such as low intension, poor rub resistance limited its range. By making use of thetechnique of laser cladding, the overall performance a material can be improved. At present,the parameters of laser processing are chosen mainly by experiment and through experience.Numerical simulation for aluminum alloys is significant for optimizing parameters of lasercladding.In this paper, laser cladding of SiC on 6061 aluminum alloy was carried out using a 2kWCW Nd-YAG laser. Finite Element Method (FEM) was used to simulate the temperature fieldduring laser cladding, some experiments were carried out to verify the simulation results. Thecalculation in cladding process is a material nonlinear procedure that the material propertieschange with the temperature; choose the function of Gauss as heat source model, we canconveniently carry out the loading and unloading of the motional heat source by using theAPDL language; A mathematic model of transient thermal process in cladding is establishedto simulate the moving of the heat source, and simultaneously appropriate mesh was plotted;The problem of the fusion and solidification of material was solved by the method ofchanging the element material; Analyze the distribution of the temperature fields from theaspect of laser cladding process. The author systemically discussed the finite elementanalytical system of the cladding process by realizing the 3D dynamic simulating of lasercladding temperature field, then used the research result to simulate the cladding process ofsurfacing by FEM soft ANSYS. The microstructure, phase identification of the modifiedlayers were examined using scanning electron microscopy (SEM), X-raydiffractometer(XRD), respectively. Proving the result according to the simulation result.In this paper, a feasible dynamic simulation method on 3D cladding temperature fieldwas established, which provided theory foundation and instruction on optimizing the claddingtechnology and parameters. The simulated results show that the laser parameters can decidesamples’ peak temperature on the surface and the distribution of temperature grads. The maximum temperature in the field was inversely proportional to the sweep speed and thefacular radius, and directly proportional to the laser power. The temperature grad was affectedlowly by sweep speed, but highly by laser power and facular radius. The experimental resultsshow mostly conformity compared with the simulated results. The best technology parameteris: laser power 1200W, sweep speed 5ram/s, facular radius 1.25mm.更多还原