Strength of silver brazed joints in mild steel

An investigation was made of the dependence of the strength of silver brazed, low carbon steel joints on the geometry of the joint. The experimental results indicate that for cylindrical test specimens having transverse brazed joints, the ultimate tensile strength is really a linear function of the thickness to diameter ratio rather than only of the thickness of the filler metal for constant specimen diameter.     

厚板铝合金FSW和MIG焊接接头疲劳性能

对厚度10 mm的6082-T6铝合金搅拌摩擦焊(FSW)和MIG焊接接头的疲劳强度进行了试验研究,并与6082-T6母材疲劳性能进行了对比分析.结果表明,6082-T6母材的疲劳S-N曲线最高、MIG焊接接头S-N曲线度最低,而FSW接头的疲劳S-N曲线近似位于两者之间;在高应力区FSW疲劳强度低于MIG焊接接头、而在低应力区高于MIG焊接接头.大部分FSW试样疲劳裂纹启始于焊缝根部的"弱连接"缺陷,采用机械加工去掉1.4 mm厚度焊缝根部材料后,FSW疲劳强度明显提高并接近母材数据.厚板6082-T6铝合金FSW焊缝根部质量控制是影响疲劳性能的关键因素.     

铟对低银Ag-Cu-Zn钎料显微组织和性能的影响

研究了低银Ag-Cu-Zn钎料(ωAg≤20%)的熔化特性、铺展性能、钎料显微组织。以黄铜/304不锈钢作为母材,采用火焰钎焊方法,进行了搭接钎焊试验。结果表明,低银Ag-Cu-Zn钎料显微组织主要由铜基固溶体、银基固溶体、Cu Zn化合物相构成。In的添加降低了Ag-Cu-Zn钎料的固、液相线温度,改善了钎料润湿性能;添加In的低银Ag-Cu-Zn钎料在凝固过程中析出富In的银基固溶体,起到了固溶强化的效果,改善了钎焊接头的显微组织,从而提高了钎缝接头的力学性能。使用17Ag Cu Zn-1In火焰钎焊黄铜/304不锈钢,钎焊接头成形美观、组织致密、无缺陷存在,综合性能与含银量为25%的BAg25Cu Zn Sn银钎料的性能相当,节银效果显著。     

铝锂合金钎焊接头断口组织与性能

采用金相显微镜、扫描电镜、硬度计等测量方法,观察分析了铝锂合金钎焊前后母材和钎焊接头的显微组织变化,通过分析测试钎焊接头的显微硬度和断口微区的化学成分,研究分析了钎焊接头强度的变化规律.结果表明,焊后母材中的强化相由质点转变为板条状;氮气保护条件下,钎焊接头未见气孔、夹杂、裂纹等缺陷,钎焊接头存在一定的扩散区,从而有效地提高了钎焊接头的强度;无氮气保护的条件下,钎焊接头有大量的缺陷存在,这些缺陷的存在严重影响了钎焊接头的强度.     

采用冷喷涂铜涂层做中间层的镁合金与钢共晶接触反应钎焊工艺及接头性能

采用厚度为50 μm的冷喷涂铜涂层作为中间层,研究了连接温度和保温时间对AZ31B镁合金/钢异种金属接触反应钎焊接头剪切强度的影响规律.通过金相显微镜、扫描电镜（SEM）、X射线衍射仪（XRD）、显微硬度和剪切强度试验,研究了AZ31B镁合金/钢钎焊接头界面微观组织和力学性能.结果表明,当连接温度为530℃,保温时间为60 min时,接头剪切强度达到最大值36.9 MPa.AZ31B镁合金/钢钎焊接头界面反应产物主要为Mg₂Cu,α-Mg固溶体和Mg-Cu-Al三元相.Mg-Cu-Al三元相的尺寸和分布,以及08F钢侧是否存在Mg₂Cu共晶相共同决定了接头的强度.由钎焊接头断口可知,最佳工艺参数下断裂方式为脆性断裂与韧性断裂的混合方式.     

Very low cycle fatigue properties of butt welded joints containing weld defects. Study of acceptable size of defects in girth welds of gas pipelines

Summary

This paper describes an investigation of the very low cycle fatigue strength of HT570 steel welded joints containing weld defects to determine the acceptable size of weld defects in girth welds of underground gas pipelines subjected to cyclic ground displacements due to earthquakes. Butt welded joints containing incomplete penetration (IP), blowholes (BH), lack of fusion in theintermedi‐ate pass (LF), and cracks in the penetration bead (CR) were prepared and tested under strain‐controlled conditions. All specimens tested in the present research study satisfy the fatigue design curve for girth welds of underground gas pipelines. The fatigue strength of specimens containing weld defects generally decreases with an increasing equivalent defect size. The shape of a crack initiated from a defect is affected by the reinforcement, with the surface crack propagating rapidly along the weld toe of the penetration weld over the width of the specimen. The relationship between the J‐integral range and the crack propagation rate under a very low cycle fatigue load is virtually the same as the extension of the relationship in the low J‐integral range. A crack propagation analysis based on the defect being regarded as a crack is performed to determine the relationship between the defect size and the number of cycles over the plate thickness. The critical size of defects in welds of gas pipelines under cyclic ground displacements is proposed by the analysis. The critical crack size of surface defects is applicable to buried defects, because surface defects give a more conservative evaluation than buried defects. The analytical results provide more conservative estimations than the experimental ones.     

Ultrasonic guided wave inspection of Inconel 625 brazed lap joints: Simulation and experimentation

The aerospace industry has been investigating the use of structural brazed joints. As a result of this effort, there is now a need for a rapid, robust, and cost-effective non-destructive testing method to evaluate the structural integrity of the joints. The mechanical strength of brazed joints is known to depend on the microstructural quantity of brittle phases. Ultrasonic guided waves offer the possibility of detecting brittle phases in joints using spatio-temporal measurements. This study focused on the development of a technique based on ultrasonic guided waves for the inspection of Inconel 625 lap joints brazed with BNi-2 filler metal. A finite element model of a lap joint was used to optimize the inspection parameters and assess the feasibility of detecting the quantity of brittle phases in the joint. A finite element parametric study simulating the input signal shape, the center frequency, and the excitation direction was performed. The simulations showed that the ultrasonic guided wave energy transmitted through, and reflected from, the joints was proportional to the amount of brittle phases in the joint. Experimental validations were then performed on three distinctive samples with variable amount of brittle phases in the joint. The samples had three different brazing times (1, 60 and 180 min). Finally, experimental results were in accordance with simulations and demonstrate the potential of the inspection method to estimate the quantity of brittle phases in a lap joint.     

化学镀锡钎料钎焊黄铜的接头组织和力学性能

采用化学镀方法在BAg45CuZn钎料表面镀覆微米锡层,并用镀锡银钎料以火焰钎焊工艺连接H62黄铜。借助金相显微镜、扫描电镜(SEM)和X射线衍射仪(XRD)分别分析锡化学镀层、H62黄铜钎焊接头的显微组织和物相,并利用万能拉伸机和SEM表征钎焊接头的抗拉强度和断口形貌。结果表明,锡化学镀层结晶晶粒呈现明显的(110)、(210)择优取向,化学镀锡银钎料连接的接头中母材与钎缝结合紧密,接头组织中富Cu相减少,出现Cu_5Zn_8化合物相。随着基体钎料表面镀锡含量升高,钎焊接头的抗拉强度呈现先升高后降低趋势。在化学镀锡含量为6.0%(质量分数)时,钎焊接头的抗拉强度为353MPa。镀锡前后钎焊接头的拉伸断口均呈现韧性断裂。     

Nb／Al2O3钎焊界面的网状分割效应

首次研究了在Ａｌ２Ｏ３陶瓷与金属Ｎｂ的钎焊面之间加入一层金属Ｍｏ网,可大幅度提高接头的焊接强度,经用Ｎｉ５１Ｔｉ４９和Ｃｕ５２Ｎｉ１８Ｔｉ３０两种钎料焊接,焊后强度均提高５０％以上,断裂特征由陶瓷中的大块破损转变为沿界面的混合型断裂。金属网的加入对钎料凝固收缩应力产生了分割相消的作用,从而有效降低了焊接接头的残余应力。     

Microstructure and mechanical properties of AlSiCu_(10-10) filler meter brazing 6063 aluminum alloy

AlSiCu_(10-10) flame brazing 6063 aluminum alloy was rearched,and microstructure and mechanical properties of brazed joints were tested in the experiments. The interfacial microstructures and brazing phases of brazed joints were analyzed by scanning electron microscopy( SEM) and X-ray energy dispersive spectroscopy( EDS). The strength of brazed joints was aquired by tensile test. The results show that the AlCu_2 and Mg_2 Si phases were formed in the brazing seam,the former is the brittle phase,the Mg_2 Si phases is considered to be the strengthening phase of the aluminum alloy,which can reduce the brittleness caused by AlCu_2. The average tensile strength of brazed butt joint was 115 MPa,and the average shear strength of brazed joint was 26 MPa. Finally,the fracture form and fracture morphology of the brazed joint were analyzed.     

3003铝合金中温钎焊接头力学性能与显微组织

采用不同Al元素含量的中温Zn-Al钎料钎焊3003铝合金,研究了钎焊接头的力学性能及显微组织.结果表明,使用改进的CsF-AlF3钎剂,Zn-Al钎料在3003铝合金上具有良好的铺展性能.随着Al元素含量的增加,钎料在3003铝合金上的铺展性能明显改善,当Al元素含量为15%(质量分数)时铺展面积达到最大.且钎焊接头...     

热处理对Al0.5CoCrFeNi高熵合金钎焊接头组织及性能的影响

采用TiZrCuNi钎料对Al_0.5CoCrFeNi高熵合金进行钎焊连接后对其进行退火处理,研究了800 ℃下不同退火时间对钎焊接头微观组织和力学性能的影响。通过扫描电镜(SEM)、能谱仪(EDS)分析了钎焊接头微观组织及相组成,利用万能试验机测定了热处理前后试样的剪切性能。结果表明,钎焊接头的典型微观组织分为焊缝区、熔合区和热影响区3部分,焊缝区的组织主要为高熵合金相和BCC结构的FeCr基固溶体;随着退火保温时间的延长,钎焊接头焊缝区灰色相中逐步析出细小的黑色相,对接头起到了一定的弥散强化作用,微观组织更为均匀细小,钎焊接头的剪切强度由未经退火处理的554.8 MPa增加到退火12 h后的581.1 MPa。     

Load-carrying capacity of combined brazed butt joints

The special features of operation of combined brazed butt joints under loading are investigated. It is shown that to increase the load-carrying capacity of these joints, it is necessary to increase the number of steps in joints. The experimental results show that the thickness of the brazed joint in the butt and lap parts of the joint is an important design parameter which controls the efficiency of the stepped joint. An increase in the number of steps reduces the strength of the effect of natural strength of the brazed joint on the limiting load-carrying capacity of the butt joint.     

Al6061/TA2异种金属冷金属过渡焊接性分析

以AlSi₅ 焊丝对6061铝合金和TA2纯钛进行CMT熔钎焊,采用SEM,EDS分析焊接接头的微观组织特征,并通过拉伸试验对接头进行力学性能评定.结果表明,焊接过程稳定,焊缝成形美观.所得到的焊接接头具有熔焊和钎焊两部分,其中局部熔化的铝母材与熔融的焊丝混合后形成焊缝,焊缝金属与微熔的钛母材形成三个钎焊界面.钎焊界面主要成分为TiAl₃金属间化合物,其厚度较薄.此外,界面附近还有一些随机分布的棒状的TiAl₃金属间化合物.焊接过程中,随着焊丝偏移量的增加,焊缝力学性能提高.参数优化后的接头抗拉强度较高,且断裂在铝热影响区.     

钨铜/铍青铜异质钎焊界面组织与性能

采用BAg56CuZnSn,BAg50ZnCdCuNi和BAg49ZnCuMnNi银钎料实施了钨铜合金/铍青铜异质材料接头的感应钎焊连接,研究了其钎焊界面组织与力学性能.结果表明,3种银钎料均能获得完好界面钎焊接头,钎料与钨铜和铍青铜形成较好冶金结合.钎料与铍青铜界面冶金结合充分,形成明显互扩散区.钎料与钨铜钎焊界面清晰,且钎料向钨铜近界面区域形成明显扩散渗入现象.强度测试表明,BAg49ZnCuMnNi钎焊接头强度最高,达到250 MPa,接头断裂均发生在钨铜侧钎焊界面.分析表明,钎料向钨铜渗入明显促进界面结合,钎料中添加镍,由于镍与钨的扩散互溶进一步提高界面冶金结合,Mn元素添加明显细化钎缝晶粒,接头强度显著提升.     

Pulsed phase thermography imaging of fatigue-loaded composite adhesively bonded joints

We applied pulsed phase thermography to image and size damage in adhesively bonded joints. Specifically, the initiation and propagation of fatigue-induced damage in single lap joints with carbon fiber epoxy adherends was investigated. Lap joint specimens with various levels of manufacturing defects were fabricated and loaded in low-cycle fatigue. A calibration specimen with artificial defects was used to design a threshold algorithm for sizing of the damaged regions. The dominant failure mode in specimens without manufacturing defects was fiber-failure, whereas joints failing prematurely demonstrated adhesive failure. Imaging of the lap joints after regular number of fatigue cycles revealed that manufacturing defects could be detected and the resulting, imminent adhesive failure could be identified prior to joint failure. Additionally, the extent of this damage could be accurately estimated through the sizing algorithm. Due to the brittle nature of fiber-failure, it could not be detected prior to failure of the joint, however this was not critical, as the goal was to identify premature failure of the adhesively bonded joint.     

Laser welding/brazing of 5182 aluminium alloy to ZEK100 magnesium alloy using a nickel interlayer

Aluminium alloy and magnesium alloy were successfully joined by using laser welding/brazing technology via a nickel interlayer. Microstructure and mechanical properties of the dissimilar Al/Mg joints with and without a nickel interlayer were comparatively investigated. No joints were achieved without a nickel interlayer; after welding, specimens were separated without applying any force. By inserting a nickel interlayer, sound metallurgical bonding were obtained at the interfaces. Hence, the joint strength reached 410 N with the failure at Mg/Ni interface. The influence of Ni interlayer on the weld defect, microstructure and joint strength was studied, and the joint formation mechanism was also discussed.     

TIG熔修对7N01铝合金焊接接头疲劳性能的影响

采用焊条电弧焊的方法对7N01铝合金焊接试板进行TIG熔修,对熔修前后的试件进行疲劳寿命测试,并对焊接接头的显微硬度变化进行测试,采用扫描电镜对疲劳断口进行显微形貌分析,并对疲劳源区缺陷进行XRD成分检测.结果表明,TIG熔修对焊趾应力集中的降低有限,还可能引入新的焊接缺陷成为疲劳裂纹源;同时TIG熔修使得焊接区域经受二次加热,沉淀强化相的形态和重新分布造成接头组织弱化,降低了焊接接头抵抗疲劳裂纹扩展的能力,多方面作用的结果是:经TIG熔修后铝合金焊接接头疲劳寿命略有降低,所以对于7N01高强铝合金对接接头单纯采用焊趾TIG熔修的方法提高疲劳性能不具备可行性.     

Cr对Ni-P系钎料钎焊不锈钢接头性能的影响

研究了钎焊温度对Ni-P系钎料铺展件能及其真空钎焊OCr13不锈钢接头力学性能的影响.结果表明,Ni-P系钎料铺展面积随钎焊温度的升高而增大,并且相同温度下不含Cr的Ni-P钎料铺展面积大于Ni-Cr-P的铺展面积;钎焊温度从925℃升高到1000℃过程中,Ni-P、Ni-Cr-P钎料钎焊不锈钢接头的室温剪切强度均增大,并且在相同钎焊工艺下,不含Cr的Ni-P钎料钎焊不锈钢接头室温剪切强度优于Ni-Cr-P钎焊接头强度30～40MPa;Ni-P系钎料钎焊接头高温强度随温度升高而下降,测试温度超过500℃时,相同温度下含Cr的钎料能够提高钎焊接头强度0～30 MPa.     

High-temperature brazing of molybdenum to 12Cr18Ni10Ti steel with the CTEMET 1301 rapidly quenched nickel brazing alloy

Extensive studies are being carried out to develop a divertor (Divertor: a device in a thermonuclear reactor, intended for receiving of particle flows and radiation from the periphery of the plasma column. It is the most heavily loaded part of the reactor chamber surfaces with energy fluxes.) for tokamaks with a container for supplying liquid metal to the reception surface, with the construction of actual structures with high reliability and long service life. In this case, it is necessary to develop methods for joining dissimilar materials. In the transition section, molybdenum and steel (12Cr18Ni10Ti) pipes are joined by brazing. In this work, the method of producing a strong, heat resisting and hermetic joint between molybdenum and 12Cr18Ni10Ti corrosion-resisting steel is developed. Brazing is carried out using a paste based on CTEMET-1301 brazing alloy. The method of assembling the components in order to produce optimum gaps in brazing resulting in the homogeneous brazed joint without the formation of a brittle eutectic interlayer is developed. The brazed specimens were tested for heat resistance, leak tightness and service life at the given load. All the specimens withstood the tests. The mechanical properties of the brazed joints were determined by measuring the microhardness of the region of the welded joint and by shear tests. The results show that the strength characteristics depend strongly on the size of the gap between the brazed components. For the specimens assembled with the optimum gap the ultimatum shear strength was 500 ± 50 MPa.