Effect of fusion welding processes on tensile properties of armor grade,high thickness,non-heat treatable aluminium alloy joints

AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.     

Comparative study on transverse shrinkage,mechanical and metallurgical properties of AA2219 aluminium weld joints prepared by gas tungsten arc and gas metal arc welding processes

Aluminium alloy AA2219 is a high strength alloy belonging to 2000 series. It has been widely used for aerospace applications, especially for construction of cryogenic fuel tank. However, arc welding of AA2219 material is very critical. The major problems that arise in arc welding of AA2219 are the adverse development of residual stresses and the re-distribution as well as dissolution of copper rich phase in the weld joint.These effects increase with increase in heat input. Thus, special attention was taken to especially thick section welding of AA2219-T87 aluminium alloy. Hence, the present work describes the 25 mm-thick AA2219-T87 aluminium alloy plate butt welded by GTAW and GMAW processes using multi-pass welding procedure in double V groove design. The transverse shrinkage, conventional mechanical and metallurgical properties of both the locations on weld joints were studied. It is observed that the fair copper rich cellular(CRC) network is on Side-A of both the weldments. Further, it is noticed that, the severity of weld thermal cycle near to the fusion line of HAZ is reduced due to low heat input in GTAW process which results in non dissolution of copper rich phase. Based on the mechanical and metallurgical properties it is inferred that GTAW process is used to improve the aforementioned characteristics of weld joints in comparison to GMAW process.     

Pulsed current and dual pulse gas metal arc welding of grade AISI: 310S austenitic stainless steel

The transverse shrinkage, mechanical and metallurgical properties of AISI: 310 S ASS weld joints prepared by P-GMAW and DP-GMAW processes were investigated. It was observed that the use of the DP-GMAW process improves the aforementioned characteristics in comparison to that of the P-GMAW process. The enhanced quality of weld joints obtained with DP-GMAW process is primarily due to the combined effect of pulsed current and thermal pulsation(low frequency pulse). During the thermal pulsation period, there is a fluctuation of wire feed rate,which results in the further increase in welding current and the decrease in arc voltage. Because of this synchronization between welding current and arc voltage during the period of low frequency pulse, the DP-GMAW deposit introduces comparatively more thermal shock compared to the P-GMAW deposit, thereby reducing the heat input and improves the properties of weld joints.     

Microstructure and pitting corrosion resistance of AA2219 Ale Cu alloy friction stir welds e Effect of tool profile

AA2219 Ale Cu alloy is widely used in defence and aerospace applications due to required combination of high strength-to-weight ratio and toughness.Fabrication of components used for defence always involves welding.Even though the mechanical properties of the base metal are better,but the alloy suffers from poor mechanical and corrosion properties during fusion welding.To overcome the problems of fusion welding,friction stir welding(FSW) is recognized as an alternative solid state joining method aimed to improve the mechanical and corrosion properties.Tool profile is one of the important variables which affect the performance of the friction stir weld.In the present work the effect of tool profile on the microstructure and pitting corrosion of AA2219 aluminiumecopper alloy was studied.Electron backscattered diffraction results established that the grain size and orientation of weld nugget of triangle profile is finer than that of conical profile.Differential scanning calorimetric results show the evidence of precipitate dissolution during FSW.It was found that the microstructure changes,such as grain size and its orientation precipitate dissolution during FSW influence the hardness and corrosion behaviour.Pitting corrosion resistance of friction stir welds of AA2219 was found to be better for triangle profile tool compared to conical profile which is attributed to material flow and strengthening precipitate morphology in various zones.Higher amount of heat generation during FSW made using triangle profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone and coarsening in thermo mechanically affected zone(TMAZ) and heat affected zone(HAZ).     

Effect of welding processes and consumables on fatigue crack growth behaviour of armour grade quenched and tempered steel joints

Quenched and Tempered (Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking (HIC) in the heat affected zone (HAZ) after welding. The use of austenitic stainless steel (ASS) consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q&T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic steel (LHF) consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. The use of ASS and LHF consumables will lead to distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the fatigue crack growth resistance of armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence of welding consumables and welding processes on fatigue crack growth behaviour of armour grade Q&T Steel joints. Shielded metal arc welding (SMAW) and Flux cored arc welding (FCAW) were used for fabrication of joints using ASS and LHF consumables. The joints fabricated by SMAW process using LHF consumable exhibited superior fatigue crack growth resistance than all other joints.     

无电焊接热循环测试研究

利用热电偶测试了无电焊接过程中同一厚度钢板不同位置、不同厚度钢板同一位置处的焊接热循环曲线,探讨了无电焊接热循环规律及焊接母材厚度对无电焊接热循环的影响。研究表明：无电焊接时,焊件上不同位置点的热循环曲线与电弧焊基本相似。但相较而言,无电焊接在加热阶段的升温速度与冷却阶段的降温速度均显著小于电弧焊。无电焊接过程中,焊件上离焊缝中心线越近,其升温速度越大,峰值温度越高,冷却速度也越大,这一变化规律与电弧焊时完全一致。无电焊接时,焊接热量沿横向的传热速度远大于其沿纵向的传热速度,这使得焊件厚度对无电焊接的影响较为显著,也是焊件厚度增加将导致焊接难度显著增大的根本原因。     

焊接过程对焊接残余应力及残余变形的影响

采用热弹塑性有限元法 ,对直通焊和多人同时分段焊两种焊接过程的平板对接焊时焊接应力变形和圆柱壳板环缝的焊接变形进行比较 ,认为多人同时分段焊较直通焊无论在降低焊接残余应力还是焊接残余变形都具有非常显著的效果     

Gas metal arc welding of high nitrogen stainless steel with Ar-N2-O2 ternary shielding gas

High nitrogen stainless steel with nitrogen content of 0.75％was welded by gas metal arc welding with Ar—N2-O2 ternary shielding gas. The effect of the ternary shielding gas on the retention and improvement of nitrogen content in the weld was identified. Surfacing test was conducted first to compare the ability of O2 and CO2 in prompting nitrogen dissolution. The nitrogen content of the surfacing metal with O2 is slightly higher than CO2. And then Ar—N2-O2 shielding gas was applied to weld high nitrogen stainless steel. After using N2-containing shielding gas, the nitrogen content of the weld was improved by 0.1 wt％. As N2 continued to increase, the increment of nitrogen content was not obvious, but the ferrite decreased from the top to the bottom. When the proportion of N2 reached 20％, a full austenitic weld was obtained and the tensile strength was improved by 8.7％. Combined with the results of surfacing test and welding test, it is concluded that the main effect of N2 is to inhibit the escape of nitrogen and suppress the ni-trogen diffusion from bottom to the top in the molten pool.     

Gas tungsten arc welding of ZrB_2-SiC based ultra high temperature ceramic composites

The difficulty in fabricating the large size or complex shape limits the application of ZrB2-SiC composites. Joining them by fusion welding without or with preheating, controlled cooling under protective gas shield leads to thermal shock failure or porosity at the weld interface. In the present work, a filler material of(ZrB2-SiC-B4C-YAG) composite with oxidation resistance and thermal shock resistance was produced in the form of welding wire. Using the filler, gas tungsten arc welding(GTAW) was performed without employing preheating, post controlled cooling and extraneous protective gas shield to join hot pressed ZrB2-SiC(ZS), and pressureless sintered ZrB2-SiC-B4C-YAG(ZSBY) composites to themselves. The fusion welding resulted in cracking and non-uniform joining without any filler material. The weld interfaces of the composites were very clean and coherent. The Vickers micro-hardness across the weld interface was found to increase due to the increase in the volume % of both SiC and B4C in the filler material. The shear strength of the weld was about 50% of the flextural strength of the parent composite.     

Optimization of process parameters of the activated tungsten inert gas welding for aspect ratio of UNS S32205 duplex stainless steel welds

The activated TIG (ATIG) welding process mainly focuses on increasing the depth of penetration and the reduction in the width of weld bead has not been paid much attention. The shape of a weld in terms of its width-to-depth ratio known as aspect ratio has a marked influence on its solidification cracking tendency. The major influencing ATIG welding parameters, such as electrode gap, travel speed, current and voltage, that aid in controlling the aspect ratio of DSS joints, must be optimized to obtain desirable aspect ratio for DSS joints. Hence in this study, the above parameters of ATIG welding for aspect ratio of ASTM/UNS S32205 DSS welds are optimized by using Taguchi orthogonal array (OA) experimental design and other statistical tools such as Analysis of Variance (ANOVA) and Pooled ANOVA techniques. The optimum process parameters are found to be 1 mm electrode gap, 130 mm/min travel speed, 140 A current and 12 V voltage. The aspect ratio and the ferrite content for the DSS joints fabricated using the optimized ATIG parameters are found to be well within the acceptable range and there is no macroscopically evident solidification cracking.     

直流TIG焊接电弧的数值分析

以直流钨极氢弧焊电弧为研究对象,考虑阴极几何形状,建立了轴对称电弧数值计算模型,在电流密度计算中包括了阴极区和弧柱区。采用ＳＩＭＰＬＥ算法求解磁流体动力学方程组。所得电弧弧柱温度分布与实验结果相吻合;电弧速度分布、电磁力分布、电流密度分布、压力分布等电弧参量的计算结果能较全面地反映电弧内部的作用机制。     

Microstructure and corrosion behaviour of gas tungsten arc welds of maraging steel

Superior properties of maraging steels make them suitable for the fabrication of components used for military applications like missile covering, rocket motor casing and ship hulls. Welding is the main process for fabrication of these components, while the maraging steels can be fusion welded using gas tungsten arc welding(GTAW) process. All these fabricated components require longer storage life and a major problem in welds is susceptible to stress corrosion cracking(SCC). The present study is aimed at studying the SCC behaviour of MDN 250(18% Ni) steel and its welds with respect to microstructural changes. In the present study, 5.2 mm thick sheets made of MDN 250 steel in the solution annealed condition was welded using GTAW process. Post-weld heat treatments of direct ageing(480 C for 3 h), solutionizing(815 C for 1 h) followed by ageing and homogenizing(1150 C for 1 h) followed by ageing were carried out. A mixture of martensite and austenite was observed in the microstructure of the fusion zone of solutionized and direct aged welds and only martensite in as-welded condition. Homogenization and ageing treatment have eliminated reverted austenite and elemental segregation. Homogenized welds also exhibited a marginal improvement in the corrosion resistance compared to those in the as-welded, solutionized and aged condition. Constant load SCC test data clearly revealed that the failure time of homogenized weld is much longer compared to other post weld treatments, and the homogenization treatment is recommended to improve the SCC life of GTA welds of MDN 250 Maraging steel.     

Effect of welding processes on mechanical and microstructural characteristics of high strength low alloy naval grade steel joints

Naval grade high strength low alloy(HSLA) steels can be easily welded by all types of fusion welding processes. However, fusion welding of these steels leads to the problems such as cold cracking, residual stress, distortion and fatigue damage. These problems can be eliminated by solid state welding process such as friction stir welding(FSW). In this investigation, a comparative evaluation of mechanical(tensile, impact,hardness) properties and microstructural features of shielded metal arc(SMA), gas metal arc(GMA) and friction stir welded(FSW) naval grade HSLA steel joints was carried out. It was found that the use of FSW process eliminated the problems related to fusion welding processes and also resulted in the superior mechanical properties compared to GMA and SMA welded joints.     

Microstructure and pitting corrosion of armor grade AA7075 aluminum alloy friction stir weld nugget zone-Effect of post weld heat treatment and addition of boron carbide

Friction stir welding(FSW) of high strength aluminum alloys has been emerged as an alternative joining technique to avoid the problems during fusion welding.In recent times FSW is being used for armor grade AA7075 aluminum alloy in defense,aerospace and marine applications where it has to serve in non uniform loading and corrosive environments.Even though friction stir welds of AA7075 alloy possess better mechanical properties but suffer from poor corrosion resistance.The present work involves use of retrogression and reaging(RRA) post weld heat treatment to improve the corrosion resistance of welded joints of aluminum alloys.An attempt also has been made to change the chemical composition of the weld nugget by adding B4C nano particles with the aid of the FSW on a specially prepared base metal plate in butt position.The effects of peak aged condition(T6),RRA and addition of B4C nano particles on microstructure,hardness and pitting corrosion of nugget zone of the friction stir welds of AA7075 alloy have been studied.Even though RRA improved the pitting corrosion resistance,its hardness was slightly lost.Significant improvement in pitting corrosion resistance was achieved with addition of boron carbide powder and post weld heat treatment of RRA.     

Multiobjective optimization of friction welding of UNS S32205 duplex stainless steel

The present study is to optimize the process parameters for friction welding of duplex stainless steel(DSS UNS S32205).Experiments were conducted according to central composite design.Process variables,as inputs of the neural network,included friction pressure,upsetting pressure,speed and burn-off length.Tensile strength and microhardness were selected as the outputs of the neural networks.The weld metals had higher hardness and tensile strength than the base material due to grain refinement which caused failures away from the joint interface during tensile testing.Due to shorter heating time,no secondary phase intermetallic precipitation was observed in the weld joint.A multi-layer perceptron neural network was established for modeling purpose.Five various training algorithms,belonging to three classes,namely gradient descent,genetic algorithm and LevenbergeM arquardt,were used to train artificial neural network.The optimization was carried out by using particle swarm optimization method.Confirmation test was carried out by setting the optimized parameters.In conformation test,maximum tensile strength and maximum hardness obtained are 822 MPa and 322 Hv,respectively.The metallurgical investigations revealed that base metal,partially deformed zone and weld zone maintain austenite/ferrite proportion of 50:50.     

Effect of tool pin profile on microstructure and tensile properties of friction stir welded dissimilar AA 6061e AA 5086 aluminium alloy joints

Joints between two different grades of aluminium alloys are need of the hour in many light weight military structures.In this investigation,an attempt has been made to join the heat treatable(AA 6061) and non-heat treatable(AA 5086) aluminium alloys by friction stir welding(FSW)process using three different tool pin profiles like straight cylindrical,taper cylindrical and threaded cylindrical.The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscope.The tensile properties and microhardness were evaluated for the welded joint.From this investigation it is founded that the use of threaded pin profile of tool contributes to better flow of materials between two alloys and the generation of defect free stir zone.It also resulted in higher hardness values of 83 HV in the stir zone and higher tensile strength of 169 MPa compared to other two profiles.The increase in hardness is attributed to the formation of fine grains and intermetallics in the stir zone,and in addition,the reduced size of weaker regions,such as TMAZ and HAZ regions,results in higher tensile properties.     

Experimental and numerical investigations of interface properties of Ti6Al4V/CP-Ti/Copper composite plate prepared by explosive welding

Explosive welding technique is widely used in many industries. This technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding methods. Interlayer plays an important role to improve the welding quality and control energy loss during the collision process. In this paper, the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium interlayer. Microstructure details of welded composite plate were observed through optical and scanning electron microscope. Interlayer-base plate interface morphology showed a wavy structure with solid melted regions inside the vortices. Moreover, the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of Cu–Ti, i.e. CuTi, Cu₂Ti, CuTi₂, Cu₄Ti, etc. To study the mechanical properties of composite plates, mechanical tests were conducted, including the tensile test, bending test, shear test and Vickers hardness test. Numerical simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method, Euler and Arbitrary Lagrangian-Eulerian method. The multi-physics process of explosive welding, including detonation, jetting and interface morphology, was observed with simulation. Moreover, simulated plastic strain, temperature and pressure profiles were analysed to understand the welding conditions. Simulated results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent plates. At the collision point, both alloys behave like fluids, resulting in the formation of a wavy morphology with vortices, which is in good agreement with the experimental results.     

焊接工艺对熔敷金属韧性的影响

探讨了改变焊接工艺对焊条熔敷金属冲击韧性的影响．研究表明：改变焊接工艺,将通过改变熔敷金属的化学成分,影响熔敷金属的强度和韧性;降低焊接线能量时,将降低熔敷金属中的氧含量及其氧化夹杂物的数量和大小,从而提高熔敷金属的韧性     

变极性等离子弧焊换向过程控制方法研究

通过试验证实了变极性等离子弧焊换向过程中存在电弧电流谐振现象,且不同极性的电流谐振峰值不同,依据电弧理论分析发现换向期间等效电弧电阻是一个时变量。对换向电路建模分析和仿真结果表明,在换向期间系统阻尼比为时变量,调整系统阻尼比是降低电流谐振峰值的有效途径。又根据变结构控制思想提出了新的换向控制方法,并重新设计了换向电路,显著降低了电流谐振峰值,改善了大电流焊接时换向器件的工作状态,为大功率变极性等离子弧焊电源的研制和开发提供了依据。     

多弧离子镀CrNx涂层的工艺与摩擦磨损性能

为了改善发动机活塞环的摩擦学性能和提高其使用寿命,采用多弧离子镀技术在活塞环表面制备了不同N2含量和弧电流的CrNx硬膜,采用X射线衍射技术、扫描电子显微镜、纳米硬度仪和发动机台架试验装置,分别测试了薄膜相结构、表面形貌、纳米硬度和抗高温摩擦磨损性能。研究结果表明：当N2质量分数为45%时,薄膜纳米硬度相对较高,CrNx薄膜中主要以CrN（220）相为主;随着弧电流的增加,薄膜的表面颗粒尺寸增加,当弧电流为60A时,薄膜纳米硬度相对较高。与Cr电镀层活塞环相比,CrNx涂层活塞环具有较强的抗高温粘着磨损性能。