Influence of brazing parameters and alloy composition on interface morphology of brazed diamond

Active brazing is an effective technique for joining diamond or cBN grit to metallic substrates. This technique is currently used to manufacture superabrasive, high-performance tools. The investigation of interface reactions between diamond and active brazing alloys plays an important role in understanding and improving the brazing process and the resultant tool performance. Focused ion beam (FIB) milling enabled the high resolution investigation of these extremely difficult to prepare metal–diamond joints. The interfacial nanostructure is characterized by the formation of two layers of TiC with different morphologies. First a cuboidal layer forms directly on the diamond and reaches a thickness of approximately 70 nm. Then a second layer with columnar TiC crystals grows on the first layer into the brazing filler metal by a diffusion-controlled process. The combined thickness of both TiC layers varies between 50 nm and 600 nm depending on the brazing temperature and holding time.     

The effect of weld parameters on friction stir welding of brass plates

More successful results have been obtained in butt‐ and overlap‐joining of Al‐alloy plates by a recently developed solid state joining technique, namely friction stir welding (FSW), than in more conventional fusion welding processes. In this joining technique, no fusion takes place in the joint area of the plates welded. This novel joining method also offers the potential to weld some other materials rather than Al‐alloys, such as Mg‐alloys, brasses and low strength steels. In this study, the applicability of friction stir welding to brasses, namely 90 %Cu‐10 %Zn and 70 %Cu‐30 %Zn alloys, has been investigated. The joint performance was determined by conducting optical microscopy, microhardness mesurements and mechanical testing (e.g. tensile and bend tests). The effect of welding speed on the joint quality at a given rotational speed of the stirring pin (i.e. 1600 rpm) was also determined for both alloys. The highest joint performances were obtained at a welding speed of 210 mm/min for both alloys.     

Joining of metal to plastic using friction lap welding

Friction lap welding (FLW) is a new conception of joining method developed in Joining and Welding Research Institute (JWRI). The efficiency of joining metal and plastic using FLW was demonstrated through a case study on aluminium alloy AA6061 and MC Nylon-6. The lap joints with high shear strength were obtained over a wide range of welding parameters. A linear relationship was observed between FLW parameters (R/ν)^0.5 and the thickness of melted nylon (H). The influences of FLW parameters on bubbles and shear strength were investigated. The morphologies of the fractured surfaces of AA6061 alloy fell into seven types based on the scanning electron microscopy examination. Statistical analysis showed that the contribution to shear strength of these regions followed such an order: region II > region V > region VI > region VII > region IV > region I or III.     

镁合金搅拌摩擦焊接工艺参数优化

为了优化镁合金搅拌摩擦焊接工艺参数,对5 mm厚镁合金AZ31B板材的搅拌摩擦焊接技术进行了试验研究,利用SN比实验设计,对镁合金AZ31B搅拌摩擦焊接工艺参数进行了方差分析,优化了搅拌头的材料、结构,最终确定搅拌头的材料为W6Mo5Cr4V2,结构为凹面圆台形.轴肩尺寸为12 mm.探针的根部直径为5.5 mm,端部直径为2.5 mm,长度为4.7 mm.获得镁合金AZ31B搅拌摩擦焊的工艺参数显著性顺序为旋转速度、横向速度和压力;确定了镁合金AZ31B搅拌摩擦焊的最优工艺参数为1500 r/min、47.5 mm/min、3kN.     

Structure and composition of oxide film on 5083 alloy at brazing temperature

The structure and composition of the surface oxide film on the 5083 aluminium alloy at a brazing temperature of 500°C were investigated by transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that the original γ-Al₂O₃ film on the surface of the cold rolled 5083 aluminium alloy was transformed into a complex oxide film consisting of MgO, MgAl₂O₄, and free Al atoms after heating. The thickness of this oxide film, which could be divided into two distinct layers, was approximately 130 nm. The outer layer was mainly composed of an amorphous MgO phase, while the inner layer was MgO based, with a few free Al atoms and a small number of nanocrystalline MgAl₂O₄ particles distributed in it.     

铜-铝合金CPU散热器钎焊技术研究

介绍了一种环保型钎焊膏及其在CPU散热器铝合金／铜钎焊中的应用．结合散热器的铝合金-铜结构,分析了利用钎焊膏进行钎焊的过程．结果表明,钎焊可以在气体保护炉中进行,也可利用高频电源在空气气氛中进行．钎焊时在铝散热器与铜板之间发生了明显的反应,反应的液相在深度方向上有明显的晶界优先扩展取向,当在接触点发生反应产生液相后,反应得以持续进行的驱动力是Al、Cu原子通过固／液界面向反应液相中的扩散和溶解,在母材表面以下的金属学组织为Al—Cu—X和纯Al的两相组织．LHG—S2钎焊膏钎焊铜-铝合金散热器,钎焊缝的致密性完全可以达到散热器设计的技术要求,诸如传热效率及外观等．     

The influence of laser welding parameters on the microstructure and mechanical property of the as-jointed NiTi alloy wires

The Nd:YAG laser welding was used to join the binary NiTi alloy wires with different compositions(Ti-50.0 at.%Ni and Ti-50.9 at.%Ni) which had the same diameter of 1 mm. The wires were welded with different parameters, including impulse width and welding current. The aim was to assess the influence of the laser-welding process on the microstructure and mechanical properties of the welded joint of binary NiTi wires. The optical microscopy (OM) and the metallographic microscopy (MM) were used to analyze the microstructure of the welded joints. The tensile test and the differential scanning calorimetry (DSC) were carried out to examine the ultimate tensile strength and the reverse martensitic transformation temperatures of the welded joints. It was found that the welding current and the impulse width had great influence on the quality of the welded joints, an optimal parameter combination would remove the pores and micro-cracks appeared in the fusion zone, and result in good mechanical properties such as higher fracture strength and elongation. The laser welding had a few effect on the reverse martensitic transformation temperatures of the welded joints.     

Investigation of explosive welding parameters and their effects on microhardness and shear strength

The aim of this study was to investigate the strength of explosive welded metals with the same chemical compositions. Different welding interfaces (straight, wavy and continuous solidified-melted) were used with changing explosive welding parameters [stand-off distance (s), explosive loading (R) and anvils]. Joined metals were investigated under heat-treated and untreated conditions. Results on the microstructure, microhardness, tensile shear strength and bending tests are reported. According to the experimental results, the effect of the anvil on the explosive welding process was only the joining or not-joining performance. It was shown that the bonding interface changed from a straight to a wavy structure when the explosive loading and stand-off distance were increased. For wavy interfaces, when the explosive loading was increased the wavy length and amplitude increased. Results of tensile shear and bending tests showed that heat-treated specimens have more strength than untreated samples. According to tensile shear test results, straight and wavy interfaces had similar strength. In addition, in bending tests of untreated specimens it was shown that the bending zone had some cracks.     

Infrared brazing Ti-6Al-4V and SP-700 alloys using the Ti-20Zr-20Cu-20Ni braze alloy

Great efforts have been made in brazing high-strength α-β titanium alloys below their beta-phase transformation temperature in order to obtain optimized mechanical properties. The brazing temperature of the cold roll-bonded Ti-20Zr-20Cu-20Ni foil is roughly 70 °C lower than that of Ti-15Cu-15Ni filler metal. Moreover, the detrimental Cu-Ni and Cu-Ni-Zr rich Ti phases can be greatly reduced or eliminated by properly choosing the brazing thermal cycle. This research demonstrates the potential application of Ti-20Zr-20Cu-20Ni foil in brazing titanium alloys.     

Analysis of process parameters effects on friction stir welding of dissimilar aluminum alloy to advanced high strength steel

Thin sheets of aluminum alloy 6061-T6 and one type of Advanced high strength steel, transformation induced plasticity (TRIP) steel have been successfully butt joined using friction stir welding (FSW) technique. The maximum ultimate tensile strength can reach 85% of the base aluminum alloy. Intermetallic compound (IMC) layer of FeAl or Fe₃Al with thickness of less than 1 μm was formed at the Al–Fe interface in the advancing side, which can actually contribute to the joint strength. Tensile tests and scanning electron microscopy (SEM) results indicate that the weld nugget can be considered as aluminum matrix composite, which is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Effects of process parameters on the joint microstructure evolution were analyzed based on mechanical welding force and temperature that have been measured during the welding process.     

Development of a copper-based filler alloy for brazing stainless steels

The filler alloy of nominal composition Cu–40Mn–10Ni (all in wt%) was prepared in the form of ribbon of 40 μm thick by melt spinning technique. The ribbon exhibits narrow melting zone and comprise single phase of Cu–Mn–Ni solid solution. The melt spun ribbon successfully brazed 304 stainless steel butt joints. The formation of solid solution in the joining area without any intermetallics is observed. The bonding strength of filler alloy is achieved around 456 MPa.     

不同焊接条件下TIG焊接紫铜厚板的热效应研究

为改善紫铜厚板的焊接性,采用商业有限元软件Marc对钨极气体保护焊接紫铜厚板的温度场进行模拟,并详细讨论了焊接电流以及预热温度对熔池和热影响区的影响.结果表明,熔池和热影响区均随着预热温度和焊接电流的增加而增加,因此,在采用不同的预热温度和焊接电流的组合可以得到相同尺寸的熔池,但热影响区尺寸差别很大;在20℃时采用He或N2气保护焊得到的熔池尺寸与Ar气保护预热400℃时得到的熔池尺寸基本一致,但热影响区的尺寸窄于Ar气保护预热400℃时得到的热影响区尺寸.     

Improvement in the weldability of molybdenum alloy by pre-welding solid carburising

Molybdenum (Mo),with its high chemical stability and resistance to neutron irradiation,has wide appli-cation prospects in the nuclear industry;however,the embrittlement of welded Mo joints limits its further application.In this study,the brittleness of the welded joints of Mo alloy was reduced and their strength was enhanced by adding carbon to the fusion zone (FZ) during laser welding.In the FZ of the Mo joints,carbon mainly existed as Mo2C,and some free C atoms,and MoC and MoOxCy phases were also present.The distribution of Mo2C directly influenced the bonding strength of the grain boundaries.As Mo2C was dispersedly distributed as particles or discontinuous lines at the grain boundaries of Mo,it improved the resistance of the grain boundaries to the propagation of cracks and thereby increasing their strength.However,the Mo2C phases distributed in a reticular pattern at the grain boundaries of Mo provided channels that enabled cracks to rapidly propagate,thereby reducing the resistance of the grain boundaries to crack propagation and weakening their strength.The emergence of the MoOxCy phase reduced the weakening effect of free oxygen atoms on the strength of grain boundaries of Mo.     

Friction stir welding of dissimilar materials between AA6061 and AA7075 Al alloys effects of process parameters

Dissimilar AA6061 and AA7075 alloy have been friction stir welded with a variety of different process parameters. In particular, the effects of materials position and welding speed on the material flow, microstructure, microhardness distribution and tensile property of the joints were investigated. It was revealed that the material mixing is much more effective when AA6061 alloy was located on the advancing side and multiple vortexes centers formed vertically in the nugget. Three distinct zones with different extents of materials intercalations were identified and the formation mechanism of the three zones was then discussed. Grain refinement was observed in all three layers across the nugget zone with smaller grains in AA7075 Al layers. All the obtained joints fractured in the heat-affected zone on the AA6061 Al side during tensile testing, which corresponds very well to the minimum values in microhardness profiles. It was found that the tensile strength of the dissimilar joints increases with decreasing heat input. The highest joint strength was obtained when welding was conducted with highest welding speed and AA6061 Al plates were fixed on the advancing side. To facilitate the interpretation, the temperature history profiles in the HAZ and at zones close to TMAZ were also measured using thermocouple and simulated using a three-dimensional computational model.     

Friction stir welding characteristics of different heat-treated-state 2219 aluminum alloy plates

Friction stir welding (FSW) of 2219-O and 2219-T6 aluminum alloys was performed to investigate the effects of the base material conditions on the FSW characteristics. The experimental results indicated that the base material condition has a significant effect on weld morphologies, weld defects, and mechanical properties of joints. In the 2219-O welds, no discernible interface exists between the stir zone (SZ) and the thermal-mechanically affected zone (TMAZ), and weld defects are liable to form in the lower part of the weld. In the 2219-T6 welds, there is visible interface between the SZ and the TMAZ, and a weld nugget with an “onion ring”-like morphology clearly exists. The defects are liable to form in the upper part of the weld. The strength efficiency of 2219-O joints is 100%, while that of 2219-T6 joints is only up to 82%. In addition, the two types of joints have different fracture location characteristics.     

焊接工艺参数对Q345钢平板焊接残余应力的影响

为研究焊接工艺参数对Q345钢平板焊接残余应力的影响,对采用药芯焊丝半自动焊接后的8 mm厚平板焊缝结构进行仿真模拟,在经验数值范围内设置不同的焊接工艺参数值,分析平板在横向和厚度方向的焊接残余应力分布情况。研究结果表明:横向的最大焊接残余应力分布在热影响区,且随着焊接速度的增大和焊接层间温度的降低而降低;沿厚度方向的最大焊接残余应力为115.92 MPa,位于平板中间层,随着焊接速度的增大而先减小后增大;平板焊接在横向的残余应力远大于厚度方向的应力。根据焊接残余应力的变化情况,运用二元回归分析法对横向和厚度方向的最大焊接残余应力进行函数拟合与检验,并开展多因素拟合模型的分析,得到焊接速度和焊接层间温度对焊接残余应力的综合影响规律。通过研究残余应力的变化趋势可选定焊接残余应力最小时的工艺参数范围,实现焊接工艺参数优化。     

Effect of welding processes on fatigue crack growth behaviour of AISI 409M ferritic stainless steel joints fabricated using duplex stainless steel fillers

The present investigation aims to study the effect of welding processes such as shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) on fatigue crack growth behaviour of the ferritic stainless steel (FSS) conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material and AISI 2209 grade duplex stainless steel (DSS) was used as filler metal, for preparing single pass butt welded joints. Centre cracked tensile (CCT) specimens were used to evaluate the fatigue crack growth behaviour. From this investigation, it is found that the GTAW joints showed superior fatigue crack growth resistance compared with SMAW and GMAW joints. The reasons for the superior performance were discussed in detail.     

TiNiNb形状记忆合金丝精密脉冲电阻对焊工艺分析

使用自行研制的UMN -3型精密脉冲电阻对焊机对TiNiNb形状记忆合金丝的焊接性进行了研究 ,分析了焊接电流、焊接压力、顶锻压力和保护气体等焊接参数对焊接接头微观组织和力学性能的影响规律 ,并给出某些TiNiNb形状记忆合金丝获得优质接头的工艺条件 .研究结果表明 ,所研制的精密脉冲电阻对焊机可实现TiNiNb形状记忆合金丝的优质连接 ,这对于进一步研究、开发TiNi基形状记忆合金丝的潜能 ,具有重要的理论和实际应用价值 .     

Vacuum brazing of GH99 superalloy using graphene reinforced BNi-2 composite filler

A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interfacial microstructure of brazed joints was analyzed by field emission scanning electron microscope and a transmission electron microscope. The effects of graphene addition on the microstructure evolution and mechanical properties of brazed joints were investigated, and the strengthening mechanism of graphene was analyzed. The results revealed that due to the addition of graphene, M₂₃(C,B)₆ compounds were synthesized in the γ solid solution and brittle boride precipitates near the brazing seam decreased. Graphene was effective in retarding solute atoms diffusion thus impeding the precipitation of borides. Furthermore, the low coefficient of thermal expansion (CTE) of graphene was conducive to relieve stress concentration of the brazed joints during the cooling process. The shear strengths of brazed joints were significantly improved by exerting the strengthening effect of graphene. The maximum shear strengths of the brazed joints were 410.4?MPa and 329.7?MPa at room temperature and 800?°C, respectively.     

Effect of welding parameters on microstructure in the stir zone of FSW joints of aluminum die casting alloy

The effect of the welding speed and the rotation speed on the microstructure in the stir zone has been investigated by measuring the Si particle distribution in the ADC12 alloy. The stir zone has fine recrystallized grains without dendritic structures, and the eutectic Si was uniformly dispersed in the stir zone. The size of the Si particles was statistically determined in the stir zone using image processing. The number of finer Si particles, which is formed by stirring of the tool probe, increases during the FSW. Finer Si particles are distributed more in the bottom than in the other regions, though the size of the Si particles in the base metal is the same in all the regions. The size of the Si particles decreases with increasing welding speed. However, it is not significantly affected by the rotation speed.