Acquisition and processing of coaxial image of molten pool and keyhole in Nd：YAG laser welding with high power

An experimental setup of acquiring the coaxial visual image of the molten pool and keyhole in high power Nd:YAG laser welding is introduced in this paper. It is one of the most difficult problems in acquiring coaxial image that the coaxial imaging signal of molten pool and keyhole must be separated from the laser beam with high power. This problem was resolved by designing a dichroitic spectroscope. The characteristics of imaging signal were analyzed and the coaxial image of molten pool and keyhole was acquired. A smoothing filter and a homomorphic filter were designed to remove the low frequency noise and to enhance the image according to the characteristics of imaging signal. At last, edges of molten pool and keyhole were detected and extracted based on image segmentation with threshold.     

Fabrication and optical properties of a highly transparent Nd：YAG ceramic

A neodymium doped yttrium aluminum garnet (Nd:YAG) transparent ceramic was fabricated by a solid state reaction method using commercial α-Al₂O₃, Y₂O₃, and Nd₂O₃ powders as starting materials and tetraethyl orthosilicate (TEOS) as sintering aid. The morphology and microstructure of the nanopowders and the Nd:YAG transparent ceramic were investigated. The fully dense Nd:YAG ceramic with an average grain size of ∼20 μm was obtained by vacuum sintering at 1720°C for 12 h. Few pores and grain-boundary phases were observed. The in-line transmittance of the ceramic was 81.5% at 1064 nm.     

超薄板材上Nd：YAG脉冲激光送粉熔覆研究

研究了为满足特定图案要求在超薄板材（０．１～０．１５ｍｍ）上进行Ｎｄ：ＹＡＧ脉冲激光送粉精细熔覆过程中激光熔覆特性、侧向和同轴喷嘴送粉熔覆、基体的真空吸附夹紧和强迫制冷、熔覆层几何形貌、元素分布和微观组织特性等因素。得到了熔覆层高度比为０．８８和０．５、质量良好的熔覆图案。     

Correlation between laser-wire distance and Nd：YAG laser ＋ P-GMA hybrid welding heat input parameters

In laser+P-GMA hybrid welding,laser-wire distance is an important parameter to describe the distance from laser spot to the center of the pulsed gas metal arc.The experiments results show that the optimal laser-wire distance with the deepest weld penetration increases with welding current and laser power being increased and decreases with welding speed being increased.Welding current,laser power and welding speed determine the hybrid welding heat input in laser+arc hybrid welding process,so there is a correlation between the optimal laser-wire distance and the hybrid heat input welding parameters for the deepest weld penetration: the optimal laser-wire distance increases with the heat input being increased.The positive correlation between the optimal laser-wire distance and the hybrid welding heat input is induced by the characteristics of the limited influence of P-GMA welding process on laser transmission and the dependence of weld penetration of hybrid welding on laser power.     

Microstructure and properties of Nd:YAG laser welded AZ31B magnesium alloy

Biodegradable magnesium-based alloys are very promising materials for temporary implants. Laser welding is an important joining method in such application. In this study, the as-rolled AZ31B magnesium alloy sheets of 1 mm in thickness were successfully joined by Nd ： YAG laser welding. The microstructure and properties of the welded joint were investigated. The result shows that the welded joint is characterized by a narrow heat-affected zone, finer grains and a large number of precipitates distribute in the matrix in the weld. Microhardness of the weld is significantly improved to 72 HV 0. 05 as compared to 55 HV 0. 05 of the base metal. Tensile strength of butt-welded joint is 180. 24 MPa, which is 76. 8% that of the base metal. The electrochemical corrosion experiment shows that the corrosion resistance of laser welded joint is significantly improved in a 3.5 wt. % NaCl solution.     

Nd:YAG激光焊接800 MPa TRIP钢的接头组织与性能

采用Nd:YAG激光对强度为800MPa,厚度为1.2mm的TRIP钢板进行焊接.研究焊接速度对焊缝外观和截面成形的影响及接头的组织特点、硬度、强度和成形能力.激光功率相同,焊接速度较低时焊缝易产生气孔,速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝组织主要由马氏体构成,从焊缝、热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝中出现马氏体,接头的塑性和韧性降低,板材的冲压成形能力下降.     

Nd：YAG激光-脉冲MAG复合热源焊熔滴过渡分析

采用高速摄像技术拍摄熔滴形成、长大及脱落的过程,观测并分析激光加入对电弧焊熔滴过渡的影响.结果表明,发现激光改变了熔滴的空间飞行轨迹、过渡稳定性、熔滴过渡模式.并从熔滴受力角度建立了脉冲MAG焊接熔滴力学模型,分析了激光加入后熔滴受力状态的改变情况.分析发现复合激光后,脉冲MAG熔滴还受到额外两个力的作用,即激光小孔产...     

异种金属和镀层金属的焊接

铜／镀锌钢异种金属Nd：YAG激光脉冲MIG复合热源钎接焊;硬质合金与钛合金真空扩散焊工艺研究;基于爆炸焊接的铜铝复合散热片的优化设计;外加磁场对异种金属焊接质量的影响;马氏体／贝氏体耐热钢焊接接头的界面蝠变损伤行为;     

Surface hardening of Fe-based alloy powders by Nd：YAG laser cladding followed by electrospark deposition with WC-Co cemented carbide

This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by integrating laser cladding and the electrospark deposition processes. Specimens of low carbon steel were processed firstly by laser cladding with Fe-based alloy powders and then by electrospark deposition with WC-8Co cemented carbide. It is shown that, for these two treatments, the electrospark coating possesses finer microstructure than the laser coating, and the thickness and surface hardness of the electrospark coating can be substantially increased.     

Macrostructural and microstructural features of 1 000 MPa grade TRIP steel joint by CO2 laser welding

Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity (TRIP) steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.     

高碳含铜TWIP钢TIG焊接头组织与性能

通过单向拉伸试验、显微组织观察、X射线衍射(XRD)和硬度测试对比研究了Fe-20Mn-3Cu-1.38C TWIP钢钨极氩弧焊(TIG)焊接接头固溶处理前后的组织和力学性能. 结果表明,固溶处理前焊缝组织为特定取向的柱状晶,整个焊缝组织晶粒粗大且分布着密集的颗粒状碳化物,热影响区(HAZ)在晶界有大量碳化物析出;固溶处理后,焊缝组织变为等轴晶,碳化物被完全固溶,焊接接头抗拉强度由953 MPa降为870 MPa,断后伸长率由41.85%提高至66.35%,低于母材性能(抗拉强度1 100 MPa,断后伸长率92.25%),但相比固溶处理前,综合力学性能显著提高;两种拉伸试样均断在热影响区,为典型韧性断裂.     

温度对TRIP钢动态拉伸性能的影响

在自制的冲击拉伸试验机上对低硅-TRIP钢的动态力学性能进行了研究。试验结果表明,在应变率ε=1350s^-1 50s^-1试验温度50℃～80℃范围内不仅伸长率上升,而且强度提高。最大均匀伸长率εu与总伸长率εt分别达到15．6％和32．1％,最大抗拉强度σb为938MPa,获得了满意的强塑性配合。     

304不锈钢激光焊接工艺及数值模拟

采用激光自熔焊接技术对304不锈钢进行平板焊接试验,并通过对比分析微观组织和力学性能结果,得出最佳工艺参数为:P=2.6 kW、v=30 mm/s、Δf=+2 mm.通过金相组织表征、X射线荧光衍射和电子背散射衍射等分析方法得出焊接接头的焊缝组织由奥氏体和铁素体组成.依据最佳工艺参数选用大型通用有限元模拟软件ABAQU...     

CO2激光焊接600 MPa DP钢接头组织与性能

采用CO2激光对抗拉强度为600MPa,厚度1.4mm的DP钢进行焊接.研究焊接速度对焊缝外观和截面成形的影响、接头的组织特点、硬度、强度和成形能力.结果表明,激光功率相同,焊接速度较低时焊缝易产生气孔,焊接速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝区组织主要由马氏体构成,从焊缝、焊接热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝出现马氏体组织,接头的塑性和韧性降低,板材的冲压成形能力下降.     

光纤激光焊接950 MPa级车用TWIP钢接头组织和性能

对950 MPa级车用孪生诱发塑性钢(TWIP950)板材进行光纤激光对接焊,分析接头微观组织和微区成分,进行显微硬度测试和室温拉伸试验,研究其不同应变速率下的拉伸性能及断裂行为． 结果表明,焊缝区奥氏体组织粗化和锰元素烧损导致其出现硬度低于母材的软化现象,而热影响区发生硬化现象． 随应变速率增加,母材与焊接接头的抗拉强度由负应变速率敏感性改变为正应变速率敏感性;母材与焊接接头的塑性随应变速率增加呈先下降再升高又下降的变化趋势． 不同应变速率拉伸后接头均断裂在焊缝区,随应变速率增加,接头韧性断裂特征未见明显变化．     

CCS-B船用钢板的不同激光焊接工艺分析

激光焊、激光填丝焊以及激光复合焊技术日趋成熟,并被一些著名船厂应用到生产上.我国造船业的激光应用研究正处于起步阶段.CCS-B是我国相当普遍的一种船用低碳钢,通常采用传统工艺进行焊接.采用以上的激光焊接工艺对CCS-B进行堆焊和对接焊,对它们宏观焊缝的差异进行分析,对相应焊缝金属的微观组织进行观察和分析.焊接金属的合金成分会影响其微观组织的形成,采用ICP-AES法对不同激光焊接工艺下的焊缝金属成分进行了检测分析.同时对接头截面的硬度进行了测试.     

高强钢CO2激光-MAG复合焊接性能

为了研究CO₂激光-熔化极活性气体保护焊（MAG）复合焊接性能,采用CO₂激光和CO₂激光-MAG复合焊接590MPa级高强度钢,对其焊接接头的显微组织和力学性能进行了研究.结果表明,激光-MAG复合焊接的焊缝金属中,MAG电弧作用区主要为珠光体和贝氏体,激光作用区主要为马氏体;激光-MAG复合焊接的焊缝金属中Mo和Mn合金元素的分布具有不均匀性;激光和激光-MAG复合焊接的试件焊接接头拉伸性能完全满足要求,焊缝强度高于基体强度;激光-电弧复合焊缝金属在-60℃～+15℃试验温度范围内的冲击韧性比激光焊缝金属高;激光-MAG复合焊接焊缝金属硬度在250～400 HV之间,高于基体金属的硬度.     

DP980激光焊接温度场模拟及力学性能研究

采用光纤激光焊接高强钢DP980,并对温度场分布进行有限元计算。结果表明焊缝中心热循环温度高达3204 ℃,迅速冷却后形成马氏体组织,硬度较母材提高30%,抗拉强度达到了1115.7 MPa,延伸率相对母材下降49.1%。回火区应力应变曲线存在明显的屈服平台,抗拉强度（850.7 MPa）明显低于母材（986.9 MPa）。焊接接头抗拉强度为母材的87.1%,延伸率为母材的32.7%。焊接接头拉伸试样和杯突试样均断于回火区。焊接接头的杯突值较母材下降32.58%,母材主应变值高于焊接接头。