脉冲激光诱导钛表面氮化的研究

介绍了在氮气气氛下,用脉冲激光照射钛表面实现钛的诱导氮化的实验结果.利用扫描电镜(SEM)、X射线衍射(XRD)和拉曼光谱对氮化表面进行了结构表征和性能分析.X射线衍射(XRD)结果显示氮化层的主要成分是a-Ti相和δ-TiN相,同时含有少量的a-Ti(N)固溶体.随着激光平均功率的增加,氮化层中δ-TiN相和α-Ti(N)固溶体含量逐渐增加,相应的氮含量也逐渐增加.纳米硬度测试结果显示氮化层的纳米硬度和弹性模量较基材钛明显增加,2mN载荷下测得氮化层的纳米硬度和弹性模量分别在11.5～15GPa和200～250GPa之间.     

钛合金薄板激光和钨极氩弧焊残余应力测试研究

采用小孔释放法对钛合金薄板激光焊和钨极氩弧焊(TIG焊)的焊接残余应力进行了测试,并分析了焊接方法、焊接线能量和焊后热处理对残余应力分布规律的影响。研究结果表明：激光焊残余应力分布规律与普通熔焊方法相似,但其分布区域较窄;在热影响区内,激光焊残余拉应力值比TIG焊的约低100MPa;在焊缝及其熔合线附近,激光焊残余应力却比TIG焊的高。对于不同线能量激光焊接,线能量越大,焊缝越宽,热影响区的残余应力也越大。焊后真空热处理能降低残余应力90％。     

Nd:YAG激光与半导体激光复合焊接对铝合金焊缝组织和性能的影响

目的 提高铝合金的焊缝抗拉强度,解决铝合金焊接过程中的裂纹缺陷。方法 采用脉冲Nd:YAG激光与半导体激光复合焊接铝合金,先用Nd:YAG激光形成焊接熔池,然后用半导体激光对熔池进行加热保温,获得无裂纹的焊缝,并对焊缝进行抗拉强度测试。结果 与单独的Nd:YAG激光焊接相比,Nd:YAG激光与半导体激光复合焊接的铝合金焊缝抗拉强度提高了50%,达到193MPa,为母材抗拉强度的90%。结论 2束激光的结合延长了熔池的冷却凝固时间,从而有效避免了热裂纹,减少了焊接缺陷,提高了焊接质量。     

TC4钛合金激光焊接应力变形有限元分析

基于ANSYS有限元分析软件,采用三维移动热源,对TC4钛合金激光焊接残余应力和变形进行了数值模拟和实验研究.结果表明:钛合金激光焊接产生很大的纵向残余应力,而横向残余应力较小.激光焊接线能量增加时,纵向残余应力拉伸区域变宽,峰值应力降低;而横向残余应力随线能量的增加而升高.在临界焊透规范以上焊接时,随焊接线能量的增大,角变形随之而减小,而横向收缩变形增大.焊件被完全穿透时,线能量对角变形的影响作用降低.钛合金激光焊接变形和残余应力实验结果与数值计算结果吻合性较好.通过焊缝金相实验分析了焊接残余应力和变形与线能量的内在关系.     

钛合金激光焊接技术研究进展及应用情况

介绍了激光焊接原理及特点,并根据钛合金激光焊接的三个典型问题,综合论述了为实现激光焊接钛合金所开展的基础研究工作,之后从焊接接头的组织性能、残余应力和变形以及应用范例来综述了钛合金激光焊接的研究进展和应用情况,为后续钛合金激光焊接的研究与应用提供参考和借鉴.     

Laserstrahlschweißen von Titanwerkstoffen unter Berücksichtigung des Einflusses des Sauerstoffes

Influence of the oxygen content in the shielding gas on microstructure and mechanical properties of laser welds of titanium and titanium alloys In the present work, a new tool concept for laser welding of titanium in high volume production has been presented and evaluated. Through the innovative application of a six‐layer metal web it is possible to calm the argon gas flow and avoid pernicious turbulences during welding. The integration of the mentioned metal web at the base of an open welding chamber allows the automated welding of highly reactive materials, such as titanium, under atmospheric pressure and inert shielding conditions. The higher density of argon relative to air offers the unique possibility to leave the chamber open on the top, so that a higher degree of flexibility than gas shielding devices for TIG welding, especially for industrial robots, is attained and can be successfully used for industrial mass production. Furthermore this device is important for welding three‐dimensional contours or to shield the regions of overlap (in overlapped joints) where shielding gas trailers are unsuccessful. By means of the presented gas shielding procedure and a modern laser welding process such as Nd:YAG laser welding, systematic investigations on the effect of oxygen on the microstructure as well as on the mechanical properties of reference bead‐on‐plate weldments could be performed for the first time. As a result of these welding trials it can be concluded that in order to avoid discolorations and hardness increase, lower restrictions to the purity of the shielding gas, in comparison to TIG welding condition, can be allowed. The maximum tolerable value of oxygen in the welding atmosphere was found to be approximately 1000 ppm for laser welding. On the contrary the maximum value for TIG welding is about 30 ppm. Further investigations on the microstructural and mechanical properties of the joints confirm that the optical quality assurance criteria for TIG welding due to the standards of aircraft construction transferable to Nd:YAG welding are.     

Nd:YAG激光焊接对铝锂合金组织和织构的影响

采用Nd:YAG激光进行了5A90铝锂合金薄板的对焊实验,借助光学显微镜、扫描电镜及EDS能谱、背散射衍射技术测试了焊缝的显微组织、合金元素分布及焊缝中的微观织构,并与母材进行了比较。结果表明:Nd:YAG激光焊接使5A90铝锂合金的微观组织和微观织构发生了很大的变化。焊缝区呈现出大量的等轴枝晶组织,这是由于焊缝中存在较多的异质形核点和较高的成分过冷度。焊缝中织构呈随机分布的状态,激光焊接完全改变了母材面心立方金属的冷轧织构组织。     

环形光斑激光塑料焊接工艺研究

目的 为了提高塑料焊接焊缝的剪切强度,满足实际生产要求.方法 采用环形光斑进行激光焊接试验,通过对激光功率、焊接速度、离焦量工艺参数进行三因素三水平正交试验,得到最佳工艺参数.结果 在最佳工艺参数条件下,即激光功率为50 W,焊接速度为150 mm/s,离焦量为5 mm时,PA66塑料焊缝最大剪切强度为21.6 MPa...     

不锈钢和钛合金异种金属焊接研究进展

不锈钢和钛合金异种焊接在化工、航空和核工业等领域均有广泛的应用,但不锈钢和钛合金因理化性能的差异,焊接界面常形成大量脆性金属间化合物,无法得到优质的焊接结果。以扩散焊、激光焊和电子束焊为主总结了不同焊接方法的工艺参数和接头组织成分对不锈钢和钛合金焊接质量的影响,展望了不锈钢与钛合金异种金属焊接的发展趋势。     

Pulsed Nd-YAG Laser Welding of A SiC Particulate Reinforced Aluminium Alloy Composite

This paper examines the laser welding behaviour of a SiC particulate reinforced Al-alloy 2124 composite using a pulsed Nd-YAG laser. The influences of laser welding parameters of laser intensity, pulse duration and the beams focus position on the depth of weld penetration as well as the size of fusion zone were investigated. These investigations have led to an optimum welding condition proposed for pulsed laser welding of SiC particulate reinforced aluminium alloy composites with minimum defects.     

TA15钛合金电子束焊缝形貌及显微组织

对TA15钛合金厚板采用电子束焊接,研究了焊接速度为400mm／min和600mm／min的工艺条件下的焊缝形状、显微组织以及接头的显微硬度。结果表明：提高焊接速度,焊缝显微组织变得细小、均匀,热影响区收窄,接头上下部位显微硬度值更为相近,曲线也较陡直。     

TA5钛合金激光填丝焊接工艺研究

采用激光填丝焊,实现了4 mm厚TA5钛合金I型坡口单道焊双面成型,研究了工艺参数对焊缝成型、气孔率和力学性能的影响,结果表明,焊缝成型美观,抗拉强度最高可达797.5 MPa,为母材的98.2%。激光功率增加,背面焊透量增加,焊缝气孔率先降低后增加,抗拉强度增加;离焦量由负离焦增加到正离焦时,焊缝的咬边缺陷消失,气孔率呈先增后降的趋势,抗拉强度增加;随着焊接速度的增加,背面焊透量降低,气孔率降低,抗拉强度略微降低。金相分析结果显示,焊接时焊缝区完全发生α→β转变,而焊后冷却速度较快,导致焊缝区在冷却过程中生成了大量的针状α′相;热影响区部分发生α→β,主要是由块状α相和锯齿状α相组成。硬度测试结果显示,焊缝中心硬度较高,母材区硬度最低,近母材热影响区到母材方向的硬度出现明显的降低;焊缝顶部的硬度值高于焊缝中心和底部的。     

Laser Welding of TC-1 Titanium Alloy

The technology of CO2 laser welding and joint properties of titanium alloy were investigated. The problem of molten pool protection was resolved by designing a shielding trailer and a special clamp. Joints with silvery appearance were obtained, which have no pore and crack. In addition, the welding speed could reach 3 m/rain for the plate of 1.5 mm thickness being penetrated. The reason of the porosity formation in partial penetration joints is that the keyholes can be easily cut apart in the radial direction, which makes the gas enclosed in the molten pool. The surface oxide of specimens can not affect the porosity formation in welds directly.     

Continuous Wave ND:YAG Laser Welding of Sand-Cast ZE41A-T5 Magnesium Alloys

A continuous wave 4 kW Nd:YAG laser system was used to weld 2-mm butt joints of sand-cast ZE41A-T5 magnesium alloys at a power of 2.5 kW, welding speed of 6.0 m/min, and defocusing distance from - 2 to + 3 mm for the material in the machined surface conditions. It was found that the adjustment of defocusing distance greatly influences the establishment of conduction or keyhole mode welding. Conduction welding is obtained at a power density of 4.0 × 10⁵ W/cm². Keyhole welding is reached at a threshold irradiance of 1.5 × 10⁶ W/cm². The fusion zone consists of refined equiaxed grains formed through cellular growth in the Zr-containing magnesium alloys. The partially melted zone is rather narrow, only a few grains wide. No grain growth or coarsening but softening is observed in the heat affected zone (HAZ). The weld defects observed include three main types: imperfect shape, cavities, and weld cracks. The mechanisms of their formations are discussed. In addition, the original cast quality was found to have a significant influence on the formation of defects such as underfill, surface depression, porosity, and burn-through during laser welding.     

Research and Progress in Laser Welding of Wrought Aluminum Alloys. I. Laser Welding Processes

With the wide application of Al alloys in automotive, aerospace and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought Al alloys have been critically discussed from different perspectives. The primary objective of this review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of Al alloy joints. Two main types of industrial lasers, carbon dioxide (CO₂) and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In this part of the review, the main laser welding processing parameters including the laser-, process-, and material-related variables and their effects on weld quality are examined. In part II of this article in this journal, the metallurgical microstructures and main defects encountered in laser welding of Al alloys such as porosity, cracking, oxide inclusions, and loss of alloying elements are discussed from the point of view of mechanism of their formation, main influencing factors, and remedy measures. In part II, the main mechanical properties such as hardness, tensile, and fatigue strength and formability are also discussed.     

Fügen von Magnesium und Magnesiumlegierungen

Welding of Magnesium and Magnesium alloys Magnesium is mainly connected by screws. In this paper the results of experiments with different welding processes will be presented. The following methods have been applied: TIG, MIG, Nd: YAG‐Laser and CO₂‐Laser welding, electron beam welding and High Power Diode Laser welding.     

激光焊接参数对钛合金薄板组织及力学性能影响

目的 研究不同激光焊接工艺参数对1 mm厚TA18薄板焊接的影响,为有效解决焊缝缺陷、脆性相等问题提供参考.方法 采用大功率碟片激光器,在氩气环境下,对1 mm厚TA18薄板进行激光焊接实验,对不同激光焊接参数下的焊接接头进行微观组织观察及力学性能测试.结果 当激光焊接功率为1.5 kW时,焊缝呈"葫芦"状,熔宽大且不...     

不锈钢与钛合金纳秒激光焊接工艺研究

目的 针对不锈钢与钛合金异种金属焊接时,容易产生间化合物,导致焊点拉力低的现象,通过纳秒激光焊接工艺来提高不锈钢与钛合金异种金属焊接的焊点拉力.方法 采用纳秒光纤激光器进行304不锈钢与TC4钛合金的焊接实验,通过激光运行螺旋线组成焊点,并对工艺参数进行正交试验,得到焊点拉力最大的工艺参数.结果 当激光功率为90 W,...     

用KrF准分子脉冲激光在低基板温度下制备AlN薄膜的研究

用KrF准分子脉冲激光在 2 0 0℃的Si(111)基板上通过改变制备条件 ,采用沉积后直接保温处理的方式制备出了具有不同择优取向的AlN薄膜 ,并得出了较高的处理温度和过长的时间不利于AlN相的形成的结论。     

Influence of laser wavelength and beam profile on Nd:YAG laser assisted formation of polycrystalline-Si films

Influence of wavelengths and beam profiles of a pulsed Nd³⁺:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd³⁺:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm² to 560 mJ/cm², where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm² to 480 mJ/cm². On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm² was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd³⁺:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization.