脉冲激光离散熔凝加工的熔池几何形态研究

研究了Ｎｄ∶ＹＡＧ脉冲激光离散加工时功率密度和作用时间对熔池几何形态的影响。５ＣｒＭｎＭｏ钢的实验结果表明：在一定加工条件下,熔池存在热传导型和深熔型两种形态。激光作用时间小于４ｍｓ时,随着激光功率密度的增加,熔池深宽比显著增加;作用时间超过４ｍｓ后,功率密度对深宽比的影响减弱。基于线性热传导模型的计算结果表明：熔凝起始阶段固态加热过程可忽略;熔池几何尺寸在激光脉冲结束后某个时刻达到最大值;当平均功率密度大于５×１０５Ｗ／ｃｍ２,同时激光作用时间大于２ｍｓ时,热传导型激光熔池向深熔型激光熔池转变     

激光快速成形过程中粉末与熔池交互作用的数值模拟

建立了描述激光快速成形过程中气/粉两相流送粉、粉末与熔池交互作用及激光熔覆成形温度场的联合模型.采用有限单元生死技术模拟了熔池形成和自由界面形状演化及熔覆层的沉积过程:根据界面温度与粉末粒子动量损失状况模拟了熔池对粒子的捕捉以及工件对粉末的反射,并采用Lagrangian粒子追踪模型实现了对粉末颗粒的跟踪.在此基础上,模拟了激光快速成形过程中316L不锈钢粉末、激光与熔池的交互作用过程.计算结果与实验结果吻合.     

光纤激光工艺参数对Q235钢穿透点焊缝形状和尺寸的影响

为了研究光纤激光工艺参数对穿透点焊缝形状和尺寸的影响，采用单因素试验方法，进行了不同激光功率、摆动幅度和焊接时间下的穿透点焊试验，分析了激光的功率密度分布、点焊缝的形状和尺寸的变化规律。结果表明，光纤激光光斑内的功率密度分布影响点焊缝的形状和尺寸。随着激光功率的增大，未摆动高斯光束形成点焊缝的形状由抛物线状逐渐转变为钟铃状，点焊缝的熔宽、熔深、深宽比和熔宽比都随之增大。光束摆动增大了激光与材料的作用面积，改变了功率密度分布和点焊缝的形状和尺寸。随着摆动幅度的增大，点焊缝的形状由钟铃状逐渐转变为碗盆状，点焊缝的熔深和深宽比都逐渐减小而熔宽比逐渐增大。当激光功率密度不变时，焊接时间对点焊缝的形状影响不大。随着焊接时间的增大，点焊缝的熔深和熔宽都逐渐增大，但深宽比基本保持不变。     

大功率激光焊熔池特性的数值模拟

用数值模拟的方法解释了大功率激光高速焊接时熔池呈窄而长形状的形成原因.在PHOENICS 3.4软件中建立了激光焊接的三维数学模型,假设小孔呈GAUSS曲面体形状,并在其上加载反蒸发力,重点考虑反蒸发力对熔池形状的影响,模拟了SUS304不锈钢在激光功率10 kW、焊速为4～20 m/min时的熔池的温度场和流场.计算结果表明,大功率激光高速焊接时喷发的等离子体加速了"匙孔"附近液态金属的流动,是大功率激光焊时产生长熔池现象的主要原因.     

45钢激光表面合金化熔池立体对流模型探讨

对４５钢上Ｆｅ基合金粉末激光表面合金化熔池，从三个不同的侧面进行了分析，在理论分析和试验的基础上，提出了激光表面合金化熔池的立体对流模型，同时，对合金层进行成分分析。结果表明：正由于熔池内部的对流，使合金层成分在宏观上趋于均匀。     

45钢激光表面合金化熔池立体对流模型探讨

对４５钢上Ｆｅ基合盒粉未激光表面合金化熔池，从三个不同的侧面进行了分析。在理论分析和试验的基础上，提出了激光表面合金化熔池的立体对流模型，同时，对合金层进行成分分析。结果表明：正由于熔池内部的对流，使合金层成分在宏观上趋于均匀。     

准分子激光微加工与熔覆特性的研究进展

介绍了准分子激光微加工的机理、特点和应用。激光微加工具有非接触、有选择性加工、热影响区域小、高精度与高重复率等优点。既可以通过材料去除方式，也可以通过材料加成方式进行微加工成形。探讨了准分子激光的熔覆特性，实验表明：准分子激光瞬时产生很高的功率密度，具有很高的温度梯度。在基体表面发生剧烈的光热交互作用；同时产生巨大的光压和等离子体．形成大量等离子体小颗粒，沉积在熔池周围。另外，由于准分子激光的脉冲作用，熔池中有明显的液相冲击波纹会影响激光熔覆层的表面质量，可以通过优化激光工艺参数改善熔覆层的表面质量。     

脉冲激光离散熔凝加工的熔池几何形态研究

研究了Ｎｄ：ＹＡＧ脉冲激光离散加工时功率密度和作用时间对熔和何形态的影响。５ＣｒＭｎＭｏ钢的实验结果表明：在一定加工条件下,熔池存在热传导热和溶熔型两种形态。     

激光熔覆溶池二维准稳态流场及温度场的数值模拟

本文建立了二维准稳态激光熔覆熔池流场及温度场的数值模型,除考虑对流换热外,模型还考虑了局部大变形自由表面,在贴体正交曲线坐标系下采用了非正交错网格ＳＩＭＰＬＥ算法离散求解动量方程,计算出了激光熔覆熔池自由表面形状和温度场,速度场及局部特征凝固参数,数值结果表明,表面张力温度系数αγ／αＴ和扫描速率ｕ０对熔池自由表面形状及熔池内温度分布,速度分布有重要影响,同时进行激光熔覆的工艺实验,实测枝晶二次臂     

钛合金激光穿透焊的焊缝成形(II)

在前文基础上进一步研究了钛合金激光穿透焊的热源作用模式及熔池流动特点对焊缝成形的影响.研究结果表明,钛合金激光穿透焊的焊缝成形是焊接过程中"两点一线"热源作用模式和熔池流动传热特点所决定的.焊接热输入和激光功率密度对"两点一线"热源作用模式及熔池流动传热特点具有重要的影响.随焊接热输入和激光功率密度的增大,金属蒸气和等离子体的热辐射以及熔池上部和熔池下部的流动传热作用增强,焊缝截面由钉形向近X形转变.根据点、线热源叠加原理获得了"两点一线"热源温度场模型.     

ON THE COMPOSITION UNIFORMITY AND SHAPE COEFFICIENT OF MOLTEN POOL BY LASER ALLOYING

The effect of the laser processing parameters on the composition uniformity and shapecoefficient of fusion zone with laser surface alloyed Cr plated on medium carbon low alloysteel has been studied.It was found that the composition uniformity depends on the shapecoefficient of fusion zone,and the later is a function of both power density and interactiontime.If the power density is fixed to a certain value,the shape coefficient is directly,propor-tional to the interaction time.A completely,uniform molten pool can be obtained,when theshape coefficient is between 1.6 and 3.0.     

Numerical simulation of molten pool dynamics in high power disk laser welding

A single-phase problem is solved rather than a multiphase problem for numerical simplicity: and the solution is based on the assumption that the region of gas or plasma can be treated as a void because solid or liquid steel has a greater density level than gas or plasma. The volume-of-fluid method, which can calculate the free surface shape of the keyhole, is used in conjunction with a ray-tracing algorithm to estimate the multiple reflections. Fresnel's reflection model is simplified by the Hagen-Rubens relation for handling a laser beam interaction with materials. Factors considered in the simulations include buoyancy force, Marangoni force and recoil pressure; furthermore, pore generation is simulated by means of an adiabatic bubble model, which can also lead to the phenomenon of a keyhole collapse. Models of the shear stress on the keyhole surface and of the heat transfer to the molten pool via a plasma plume are introduced in simulations of the weld pool dynamics. Analysis of the temperature profile characteristics of the weld bead and molten pool flow in the molten pool is based on the results of the numerical simulations. The simulation results are used to estimate the weld fusion zone shape; and the results of the simulated fusion zone formation are compared with the results of the experimental fusion zone formation and found to be in good agreement. The effects of laser beam profile (Gaussian vs. measured), vapor shear stress, vapor heat source and sulfur content on the molten pool behavior and fusion zone shape are analyzed.     

K418与42CrMo异种金属激光深熔焊接

研究了连续波Nd:YAG激光焊接功率、速度、离焦量和侧吹保护气流量对激光深熔焊接K418与42CrMo异种金属焊缝形貌、焊缝熔深的影响,讨论了焊缝区热裂纹产生机制.结果表明,额定功率为3 kW的Nd:YAG激光深熔焊接K418与42CrMo异种金属,由于它们的物理化学性质的差异,焊缝靠近42CrMo侧易出现未熔合;激光光斑向42CrMo侧偏移可以减少焊缝靠近42CrMo侧未熔合量;通过优化侧吹保护气流量和离焦量可以增加熔深.由于K418液态金属的流动性差,导致焊缝靠近K418侧对流传热不充分,使焊缝靠近K418侧熔合线呈现锯齿形.焊缝区热裂纹的产生主要是由于焊缝区元素偏析形成的低熔物导致.     

Experimental investigation on laser beam welding of martensitic stainless steels in a constrained overlap joint configuration

This paper presents experimental investigation of laser beam welding of martensitic stainless steels in a constrained overlap configuration. Experimental studies were focused on the effects of laser power, welding speed and fiber diameter on bead geometry and mechanical properties of the weld. Metallurgical study of a selected welded joint was done only to show various microstructures typically formed at different zones. Laser power and welding speed were found the most significant factors affecting the weld geometry and shearing force. The contour plots showing constant response lines indicated the evidence of two-factor interaction effects of laser power-welding speed, welding speed-fiber diameter, and fiber diameter-laser power on all the responses except the weld width. Moreover, energy density plots illustrated its linear relationship with penetration depth and limited nonlinear effects on others. Additionally, metallurgical analysis of fusion zone showed dendritic structures consisted of martensitic with eutectic ferrite along solidification grain and subgrain boundaries.     

SLM成形Cu6AlNiSnInCe仿金合金的工艺优化及其组织与性能

采用激光选区熔化(SLM)工艺成形Cu6AlNiSnInCe仿金合金,研究不同SLM工艺参数组合对试样成形质量及其组织和性能的影响。结果表明,根据SLM成形试样的形貌特征可将激光功率和扫描速度的影响直观地划分为六个区域,分别是过熔区、完全熔化区、球化区、部分熔化区、严重球化区和未成形区。在完全熔化区时,激光能量密度达到156 J/mm3,仿金粉末在该参数区域完全熔化且熔池保持稳定的状态,试样密度较高、表面质量较好,表面粗糙度为9.2μm;SLM试样由基体α-Cu(Al Ni)相和弥散分布在基体中的析出δ-Cu41Sn11相组成;SLM试样的抗变形能力、显微硬度和耐腐蚀性能均优于铸造试样。     

热输入对6A02铝合金光纤激光焊缝成形的影响

采用大功率密度的光纤激光对1.0 mm厚的6A02铝合金进行了激光焊接,着重研究了焊接热输入对焊缝宏观形貌、组织和性能的影响. 结果表明,采用高速焊接且热输入控制在8～22 J/mm范围内可以获得稳定全熔透焊缝. 典型的光纤激光焊缝横截面常呈近X形,此种形貌的焊接温度场不均匀性较小,有利于减少焊接失稳和变形. 从熔合线至焊缝中心,显微组织逐渐从柱状晶组织向混合组织(柱状晶+等轴晶)转变. 随焊接热输入的降低,焊缝区的显微组织相对细化,接头熔合线附近的软化现象逐渐减弱,焊缝区显微硬度和接头抗拉强度均略有增加.     

铝合金/镀锌钢板Nd:YAG激光+MIG电弧复合热源熔-钎焊接头的组织与性能(英文)

基于铝合金和镀锌钢在熔点上的差异,以ER4043(AlSi5)为填充材料,采用大光斑Nd:YAG激光+MIG电弧复合热源焊接工艺实现两者的熔-钎焊接,研究熔钎焊接头组织和性能。铝合金/镀锌钢板熔钎焊接头分为熔焊接头和钎焊缝两部分,熔焊缝组织由α(Al)等轴晶和晶界上短棒状的Al-Si共晶组织组成,焊趾处的富锌区为α-Al-Zn固溶体和Al-Zn共晶组织。钎焊缝为Fe-Al金属间化合物层,厚度为2~4μm,金属间化合物包括FeAl2、Fe2Al5和Fe4Al13,其中FeAl2和Fe2Al5位于近钢侧的紧密层,而Fe4Al13则呈舌状或锯齿状向熔焊缝内生长。接头抗拉强度随着焊接电流和激光功率的增大呈先增大后减小的趋势,最高可达247.3 MPa。拉伸断裂位置一般位于熔焊缝的熔合区,为以韧性断裂为主的混合断裂。接头内硬度的最大值位于钎焊缝处,然后分别沿着两侧钢板和铝合金熔焊缝逐步降低。     

Application of direct laser melting to restore damaged steel dies

Direct laser melting (DLM) technology can be applied to restore damaged steel dies. To understand the effects of DLM process parameters such as the laser power and scan rate, a series of experiments was conducted to determine the optimal operating parameters. To investigate the laser melting characteristics, the depth/height ratio, depth/width ratio and micro-hardness as a function of the laser energy density were analyzed. Fe-Cr and Fe-Ni layers were deposited on a steel die with 11.38 J/mm² of energy input. The wear-resistance and the friction coefficient of the deposited layer were investigated by a pin-on-disk test. The penetration depth decreased as the scan rate increased as a consequence of the shorter interaction time. The depth/height ratio of the deposited layer decreased with an increase in the scan rate. The depth/width ratio increased as laser power increased and the scan rate decreased. The deposition shape of the Fe-Ni powder was relatively shallow and wide compared with that of the Fe-Cr powder. The scan rate had a substantial effect upon the deposition height, with the Fe-Cr powder melting more than the Fe-Ni powder. The micro-hardness of the layer melted from the powders is higher than that of the substrate, and the hardness of the laser-surface-melted layer without any metal powder is higher compared to that of the metal-powder-melted layer. The direct laser melting process with Fe-Ni powder represents a superior method when restoring a steel die when the bead shape and hardness of the restored surface are important outcome considerations.     

Laser beam welding of dissimilar stainless steels in a fillet joint configuration

This paper investigates laser beam welding of dissimilar AISI 304L and AISI 430 stainless steels. Experimental studies were focused on effects of laser power, welding speed, defocus distance, beam incident angle, and line energy on weld bead geometry and shearing force. Metallurgical analysis was conducted on a selected weld only to show various microstructures typically formed at different zones and consequent change in microhardness. Laser power and welding speed were the most significant factors affecting weld geometry and shearing force. All the bead characteristics but radial penetration depth decreased with increased beam incident angle. The focused beam allowed selecting lower laser power and faster welding speed to obtain the same weld geometry. Weld shape factor increased rapidly due to keyhole formation for line energy input ranging from 15 kJ/m to 17 kJ/m. Fusion zone microstructures contained a variety of complex austenite-ferrite structures. Local microhardness of fusion zone was greater than that of both base metals.     

激光焊接快速凝固Ni51Ti49形状记忆合金显微组织和相变行为

文中研究了快速凝固Ni₅₁Ti₄₉形状记忆合金条(厚度1 mm)的激光焊接工艺,以及焊缝成形、接头显微组织演变、硬度分布和马氏体相变行为. 结果表明,激光功率和焊接速度对焊缝成形有显著影响,采用激光功率为700 W、焊接速度为8 mm/s的焊接工艺实现焊缝区完全熔透,并获得熔合面积适中、缺陷较少的高质量接头;激光焊接导致接头各区域呈现显著的组织不均匀性,其中母材区保留快速凝固工艺的细晶、强织构显微组织特征,热影响区为粗大等轴晶和柱状晶构成的混合晶组织,焊缝中心区为粗大的柱状晶. 激光焊接后热影响区和熔合区的维氏硬度相对母材有显著降低,其中熔合区的平均硬度最低,其值为311 HV ± 14 HV. 接头经500 ℃保温1 h无应力时效处理后,接头各区域组织的相变行为明显不同,其中冷却过程中母材区发生常规两步马氏体相变(B2–R–B19′),而焊缝区呈现多步马氏体相变行为,即先发生一步B2–R相变,随后发生两个独立的R–B19′相变.