目的 挖掘激光熔覆过程中熔池内瞬态热流动力的演化行为,是提升修复再制造部件微观结构及其力学性能的关键所在。方法 对轮胎模具钢（AISI1045）基体激光熔覆316L粉末,探究基体与粉末交互的热-流-固熔覆工艺特性,重点研究了激光能量吸收、熔池形成及微观演变的动态物理历程,构建了能量源角度（激光功率）影响下瞬态尺度下熔池形成的数值分析模型。基于表观热容方法（CALPHAD）相图计算得出基体和粉体颗粒热物理性质,利用任意拉格朗日-欧拉（ALE）动网格法实现了熔池气/液自由表面的热流动态追踪模拟,结合试验验证了温度梯度（G）和凝固速率（S）对熔池凝固微观组织形貌与枝晶尺度的合理预测。结果 熔池内马兰戈尼效应会促进热量从中心向边界扩散,激光功率从800 W增加到1 200 W,会显著增强熔池流速和熔池宽度方向的质量热传递,熔池宽度和深度显著增大,峰值温度变化幅度超过15%,熔体流速可达0.5 m/s,且基材熔化比率与激光功率成正比,导致稀释率D在0.35~0.50。瞬态热对流引起枝晶生长速率分布不均,冷却速率（G·S）自熔覆层剖面从上到下逐渐增加,枝晶间距显著减小,凝固组织逐渐向等轴晶转变。结论 提出的热输入驱动多场热-流耦合分析方法能够为熔覆层不同区域热流梯度演变及微观组织形成提供预测分析。
Abstract
Understanding transient thermo-fluid behavior within the molten pool is critical for regulating microstructural evolution and interfacial stability during laser cladding of dissimilar steels. In this study, the dynamic evolution of molten pool flow, thermal transport, and solidification behavior during laser cladding of 316L powder on AISI1045 steel is systematically investigated through an integrated numerical-experimental framework, with emphasis placed on revealing the intrinsic coupling mechanism among laser heat input, molten metal convection, dilution evolution, and microstructure formation under transient solidification conditions.
A three-dimensional transient thermal fluid coupled numerical model is established to simultaneously describe laser-material interaction, phase transformation, heat conduction, and non-isothermal molten metal flow during single-track laser cladding. Temperature-dependent thermophysical properties of both the substrate and powder materials are calculated through CALPHAD-based phase diagram analysis and incorporated via an apparent heat capacity formulation to accurately capture latent heat release during melting and solidification. The Arbitrary Lagrangian-Eulerian (ALE) dynamic mesh method is introduced to continuously track gas-liquid free-surface deformation and molten pool boundary migration. The model enables quantitative prediction of molten pool morphology evolution, internal flow structure, and temperature gradient distribution under varying laser power conditions. Numerical results are further validated through cross-sectional morphology characterization and microstructural observations of experimentally fabricated coatings. Simulation results reveal that Marangoni-driven thermo-capillary convection dominates molten pool transport behavior throughout the cladding process. Surface tension gradients induced by temperature variation drive molten metal flow from the high-temperature central region toward the cooler boundary zones, forming stable bidirectional circulation vortices within the molten pool. This convection pattern significantly enhances internal momentum exchange and thermal redistribution compared with purely conductive heat transfer. At a laser power of 800 W, temperature gradients exceedingly approximately 2 000 K are generated near the leading edge of the molten region, while velocity differences reach 0.245 m/s, accelerating localized cooling and producing pronounced spatial heterogeneity in solidification conditions.
As laser power increases from 800 W to 1 200 W, the peak temperature is increased by approximately 400 K and the maximum melt flow velocity approached 0.5 m/s, indicating intensified thermo-capillary convection and enhanced mass transport capability. Strengthened convective heat transfer promotes simultaneous expansion of molten pool width, height, and penetration depth, resulting in improved metallurgical bonding and interfacial mixing between coating and substrate. The substrate melting fraction increases monotonically with increasing heat input, producing dilution ratios ranging from 0.35 to 0.50. These quantitative results demonstrate that laser thermal input directly governs interfacial mass transfer behavior and dilution evolution during dissimilar steel cladding.
Coupled analysis of temperature gradient (G) and solidification rate (S) further establishes a quantitative relationship between transient molten pool dynamics and dendritic growth behavior. The cooling rate parameter (G·S) gradually increases from the upper region toward the bottom of the cladding layer, leading to continuous refinement of dendrite arm spacing. Experimental characterization confirms a transition from columnar dendritic structures near the clad surface to equiaxed grains close to the substrate interface. The results demonstrate that this morphology transition originates from convection-induced redistribution of thermal gradients rather than conduction-controlled solidification alone, highlighting the dominant role of melt flow in regulating solidification pathways. The proposed thermo-fluid coupling framework provides predictive capability for regional microstructure evolution and offers a physically based strategy for process optimization in laser cladding of dissimilar material systems.
关键词
激光熔覆 /
熔池演化 /
热流动力学 /
有限元模拟 /
微观组织
Key words
laser cladding /
molten pool evolution /
thermodynamics /
finite element simulation /
microstructure
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基金
山东省自然科学基金面上项目（ZR2021ME179, ZR2021ME183）; 山东省重点研发计划（2024TSGC0851）; 国家自然科学基金面上项目（52175408）
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