Fatigue crack growth behaviour of gas tungsten arc,electron beam and laser beam welded Ti–6Al–4V alloy

The present investigation is aimed to evaluate fatigue crack growth parameters of gas tungsten arc, electron beam and laser beam welded Ti–6Al–4V titanium alloy for assessing the remaining service lives of existing structure by fracture mechanics approach. Center cracked tensile specimens were tested using a 100 kN servo hydraulic controlled fatigue testing machine under constant amplitude uniaxial tensile load. Crack growth curves were plotted and crack growth parameters (exponent and intercept) were evaluated. Fatigue crack growth behavior of welds was correlated with mechanical properties and microstructural characteristics of welds. Of the three joints, the joint fabricated by laser beam welding exhibited higher fatigue crack growth resistance due to the presence of fine lamellar microstructure in the weld metal.     

Weldability of aluminium-lithium alloy 2090 using laser welding

Lithium-containing aluminium alloys are of considerable current interest in the aerospace and aircraft industries because lithium additions to aluminium improve the modulus and decrease the density compared to conventional aluminium alloys. Many such alloys are under develøpment for aircraft applications, which usually involves mechanical fastening. While aluminium-lithium alloys are fusion weldable with gas metal arc, gas tungsten arc and electron beam processes, they suffer from problems of weld porosity, heat-tearing cracking, poor penetration and low joint efficiency. In this paper, the weldability of aluminium-lithium alloys is briefly reviewed. The weldability of commercial aluminium-lithium alloy 2090 in the peak-aged condition was studied using laser welding. The quality of the welds was evaluated through mechanical tests (hardness and tensile tests) and microscopical observations. Mechanical property data and microscopical observations of the welds on prior surface-prepared (milled) material revealed a low degree of the weld surface degradation and an absence of porosity. This coupled with the attractive joint efficiencies suggest the superiority of the laser welding to conventional arc welding of this alloy. The performance of laser-welded butt joints is rationalized.     

Metallurgical characterization of pulsed current gas tungsten arc,friction stir and laser beam welded AZ31B magnesium alloy joints

This paper reports the influences of welding processes such as friction stir welding (FSW), laser beam welding (LBW) and pulsed current gas tungsten arc welding (PCGTAW) on mechanical and metallurgical properties of AZ31B magnesium alloy. Optical microscopy, scanning electron microscopy, transmission electron microscopy and X-Ray diffraction technique were used to evaluate the metallurgical characteristics of welded joints. LBW joints exhibited superior tensile properties compared to FSW and PCGTAW joints due to the formation of finer grains in weld region, higher fusion zone hardness, the absence of heat affected zone, presence of uniformly distributed finer precipitates in weld region.     

钛合金焊接凝固结晶控制的研究

由于焊缝金属中粗大的柱状β晶粒组织严重影响其力学性能及耐蚀性,钛合金焊接凝固结晶方面的研究工作一直颇受重视。综述了该方向有代表性的研究成果,并介绍了本人利用电子束扫描控制焊接凝固结晶取得的一些结果。     

Comparative evaluation of tungsten inert gas and laser beam welding of AA5083-H321

In this study, the bead-on-plate welds were made on AA5083-H321 alloy plates using both tungsten inert gas (TIG) welding and laser beam (LB) welding processes to study the enhancement of mechanical properties such as weld yield strength and hardness. The low heat input of laser beam welding effectively reduced the size of the fusion zone and heat affected zone compared to tungsten inert gas welding process. High speed LB welding and fast heating and cooling of LB welding process hinders grain growth compared to TIG welding process. The effect of vapourization of volatile alloying elements is also considered. It seems that magnesium evaporation is relatively less in LB welding compared to TIG welding. Tensile testing of the welded joints revealed that LB welding results in superior mechanical properties. It is concluded that LB welding process is more suitable to join AA5083-H321.     

Role of pulsed current on metallurgical and mechanical properties of dissimilar metal gas tungsten arc welding of maraging steel to low alloy steel

This research work encompasses the investigations carried out on the mechanical and metallurgical properties of maraging steel and AISI 4340 aeronautical steel weldments. The materials were joined by continuous current gas tungsten arc welding (CCGTA) and pulse current (PCGTA) gas tungsten arc welding processes using ErNiCrMo-3 filler wire. Cross sectional macrostructures confirmed proper deposition of the fillers and lack of discontinuities. Optical microscopy studies revealed that at the maraging steel–weld interface, martensite in distorted and block forms prevailed in CCGTA and PCGTA weldments whereas tempered martensite was predominant at the low alloy–weld interfaces of both the welds. Scanning electron microscopy (SEM) with energy dispersive analysis of X-rays (EDAX) analysis apparently showed less elemental migration in PCGTA weldments as compared to the other. Results of X-ray diffraction analysis recorded possible phase formations in various zones of the weldments. Microhardness profiles in either weld zones followed a constant trend whereas it showed a downtrend in the heat affected zones (HAZ) of the maraging steel and very high hardness profiles were observed in the low alloy steel side. Tensile studies on various factors and impact testing showed that PCGTA weldments outperformed the continuous ones in terms of strength, ductility and toughness. Fractograph analysis depicted the nature of failures of tensile and impact tested specimens. Comparison analyses involving influence and nature of pulsed current welds over continuous ones were done to determine the possibility of implementing these joining processes in aerospace applications. Weldments fabricated using PCGTA technique proved to be superior to the other, resulting in exceptional mechanical properties.     

Effect of friction stir processing on corrosion resistance of aluminum–copper alloy gas tungsten arc welds

Gas tungsten arc welds in aluminum–copper alloy AA2219-T6 were friction stir processed (to a depth of about 2 mm from the weld top surface) for improving their corrosion resistance. Unprocessed and friction stir processed welds were comparatively evaluated for their microstructural characteristics and corrosion resistance. Friction stir processing was found to result in substantial microstructural refinement with fine, uniformly distributed CuAl₂ intermetallic particles. Friction stir processing was also found to result in a more uniform copper distribution in the weld metal, leading to significant increase in weld corrosion resistance. This work demonstrates that friction stir processing is an effective strategy for overcoming corrosion problems in aluminum–copper alloy fusion welds.     

Pore formation during hybrid laser-tungsten inert gas arc welding of magnesium alloy AZ31B—mechanism and remedy

One of the major concerns during high speed welding of magnesium alloys is the presence of porosity in the weld metal that can deteriorate mechanical properties. This study seeks to analyze the presence method and quantity of pore during hybrid laser-tungsten inert gas arc (TIG) welding of magnesium alloy AZ31B by radiography, optical microscopy and electron probe microanalysis (EMPA). At the same time, it identifies both the mechanism of pore formation and a remedy for this problem. The experimental results indicate that lacking of shielding gas for laser beam is the dominant cause of macroporosity formation during the hybrid of laser-TIG welding of magnesium Alloys AZ31B plate, and hydrogen is not main cause to form large pores. A favorable weld without porosity can be obtained by appending lateral shielding gas for laser beam.     

Characterization of microstructure,mechanical properties and corrosion resistance of dissimilar welded joint between 2205 duplex stainless steel and 16MnR

The joint of dissimilar metals between 2205 duplex stainless steel and 16MnR low alloy high strength steel are welded by tungsten inert gas arc welding (GTAW) and shielded metal arc welding (SMAW) respectively. The microstructures of welded joints are investigated using scanning electron microscope, optical microscope and transmission electron microscopy respectively. The relationship between mechanical properties, corrosion resistance and microstructure of welded joints is evaluated. Results indicate that there are a decarburized layer and an unmixed zone close to the fusion line. It is also indicated that, austenite and acicular ferrite structures distribute uniformly in the weld metal, which is advantageous for better toughness and ductility of joints. Mechanical properties of joints welded by the two kinds of welding technology are satisfied. However, the corrosion resistance of the weldment produced by GTAW is superior to that by SMAW in chloride solution. Based on the present work, it is concluded that GTAW is the suitable welding procedure for joining dissimilar metals between 2205 duplex stainless steel and 16MnR.     

Crack resistance of austenitic stainless steel pipe and pipe welds with a circumferential crack under monotonic loading

This paper describes the experimental studies carried out on cracked austenitic stainless steel pipe and pipe welds under bending loads. Pipe welds were produced by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW). Fracture resistance curves for pipe and pipe welds were compared. Results indicate that the fracture resistance of pipe and pipe weld (GTAW) is comparable but that of pipe weld (GTAW+SMAW) is inferior. Cracks do not deviate from their original plane during propagation as observed in the cases of carbon steel pipe and pipe welds. The fracture resistance of pipe welds does not depend on the loading histories to which it has been subjected prior to fracture test. Initiation and crack propagation were observed prior to the maximum moment. An existing limit load expression is applicable for the pipe base material but gives non‐conservative results for the pipe welds. Multiplication factors have been suggested for the pipe welds for evaluation of limit loads using the existing expression. Fracture resistance for the pipe and compact tension specimens have also been compared for base material and welds.     

Studies on creep/stress rupture behaviour of superalloy 718 weldments used in gas turbine applications

Superalloy 718 in the solution-treated condition was welded autogenously by electron beam welding and gas tungsten are welding processes. The weldrnents after suitable heat treatment were subjected. to creep/stress rupture testing at 650°C and 690 MPa. The results showed that the Laves phase resulting in the weld metalis deterimental to the creep rupture life of weld metals when present With the continuous morphology found in gas tungsten are welds. The lower amounts and discontinuous morphology of the Laves phase in electron beam weldments in combination With favourable gramonentauon resulted in relatively better rupture properties for these weldments.     

0Cr19Ni9 TIG焊接接头的抗蚀性及电弧重熔

研究了低碳奥氏体不锈钢０ｃＲ１９Ｎｉ９手工钨极氩弧焊（ＴＩＧ）焊接接头表面抗蚀性能及电弧重熔对其抗蚀性能的影响。实验结果表明,受焊接热循环的作用,焊接接头热影响区的抗蚀性能,以及焊缝金属的抗蚀性能,较母材有所降低。但经微束等离子弧表面重熔后,由于接头表面重熔层的快速凝固作用,细化了支组织,减小了显微的,抑制了碳铬化合物在晶界的沉淀析出,焊接接头的抗蚀性能得以显著提高。     

Fatigue crack growth resistance of gas tungsten arc,electron beam and friction stir welded joints of AA2219 aluminium alloy

AA2219 aluminium alloy square butt joints without filler metal addition were fabricated using gas tungsten arc welding (GTAW), electron beam welding (EBW) and friction stir welding (FSW) processes. The effect of three welding processes on fatigue crack growth behaviour is reported in this paper. Transverse tensile properties of the welded joints were evaluated. Microstructure analysis was also carried out using optical and electron microscopes. It was found that the FSW joints are exhibiting superior fatigue crack growth resistance compared to EBW and GTAW joints. This was mainly due to the formation of very fine, dynamically recrystallised grains and uniform distribution of fine precipitates in the weld region.     

Effect of Pulsed Current TIG Welding Parameters on Pitting Corrosion Behaviour of AA6061 Aluminium Alloy

Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.     

Laser welding of oxide dispersion-strengthened alloy MA754

Conventional arc-welding of MA 754, an oxide dispersion-strengthened (ODS) superalloy, poses two significant problems: agglomeration of dispersoids and weld solidification grain boundaries perpendicular to the rolled direction, both of which reduce the high-temperature creep and stress rupture properties. In the present work, laser welding of MA 754 alloy was conducted to determine the effects of a high energy density source on the microstructure and mechanical properties of a 3.2 mm thick butt joint. Tungsten-inert-gas (TIG) welding was also studied for comparison purpose. X-ray diffraction, optical microscopy and scanning electron microscopy analysis coupled with tensile, hardness and hot corrosion tests were used to evaluate the performance of weldments. Results indicated the absence of dispersoid agglomeration and superior tensile and corrosion properties of laser weldments over arc welds. The properties of laser weldments are comparable to those of wrought MA 754.     

The effect of preheat & post weld heat treatment on the laser weldability of AISI 420 martensitic stainless steel

The martensitic stainless steels are widely used in many industries with their excellent mechanical properties and sufficient corrosion resistance. These steels usually are used for a wide range of applications like nuclear power plants, steam generators, mixer blades, pressure vessels, turbine blades, surgical tools, instrument manufacturing and so on. Contrary to good mechanical and corrosion properties of martensitic steels, poor weldability and cold cracking sensitivity are major problems that are faced in joining of these steels. In this study, the weldability of AISI 420 (X30Cr13) martensitic stainless steel by CO₂ laser beam welding method has been investigated. Effects of pre and post weld heat treatments on mechanical properties and microstructure of laser welded AISI 420 martensitic stainless have also been determined. As a conclusion, it was determined that pre and post weld heat treatments sufficiently improved the mechanical properties of the welds.     

Corrosion evaluation of multi-pass welded nickel–aluminum bronze alloy in 3.5% sodium chloride solution: A restorative application of gas tungsten arc welding process

In this research, the corrosion behavior of a gas tungsten arc welded nickel–aluminum bronze (NAB) alloy is investigated by DC and AC electrochemical techniques in 3.5% sodium chloride solution. Regarding the electrochemical impedance spectroscopy and potentiodynamic results, uniform corrosion resistance of instantly immersed weld and base samples are almost analogous and increased (more in weld region) during the immersion times. Moreover, zero resistant ammeter results demonstrated that the few nanoampere galvanic currents are attributed to microstructural and morphological differences between these two regions. Therefore, the welding procedure could not deteriorate the general corrosion resistance of the restored damaged NAB parts operating in marine environments.     

Influence of intrinsic and extrinsic factors on mechanical properties of 2090 aluminium alloy weldments

Abstract

Intrinsic and extrinsic factors that influence the mechanical properties of as welded weldments in an Al–Cu–Li alloy, 2090, have been investigated. Electron beam (EB) and gas tungsten arc (GTA) welds were produced in 2090–T3 and 2090–T8. The tensile properties of as welded and solutionised and aged weldments at 293 and 77 K are presented. The results show that differences in thermomechanical processing between the base metal and the fusion zone lead to inhomogeneities in the weldment microstructure and, consequently, differences in properties. In the as welded condition, the EB and GTA fusion zones lack the strengthening precipitates present in the base metal. As a result, increased base metal constraint on the as welded fusion zone confines the plastic deformation to within the weld and therefore the measured mechanical properties of the weldment are those of the weld material. After equivalent thermal processing, the properties of the EB and GTA weldments are as good as, or better than, those of the base metal. In the post-weld solutionised and overaged condition, the base metal lacks the volume fraction and homogeneity of strengthening precipitates found in the EB and GT Afusion zones, and as a result failure occurs in the base metal.

MST/1405     

Stellite 21 coatings on AISI 410 martensitic stainless steel by gas tungsten arc welding

Abstract

Degradation of AISI 410 martensitic stainless steel, a typical alloy for many applications such as steam turbine blade, could impair its efficiency and lifetime. To overcome this problem, critical surfaces could be modified by weld cladding via gas tungsten arc welding technique. In the present research, a comparative study of Stellite 21 weld overlays deposited in three different thicknesses, i.e. dilutions, at various preheat and post-weld heat treatment temperatures on the surface of AISI 410 martensitic stainless steel, has been made. The surface of coatings has been examined to reveal their microstructures, phase characterisation and mechanical properties using XRD, microhardness tester and metallographic techniques. The results showed that the deposition of Stellite 21 coating on AISI 410 martensitic stainless steel improved its corrosion resistance. Moreover, the volumetric dilution had a considerable effect on the hardness, microstructure and electrochemical corrosion behaviour of Stellite 21 weld overlays.     

Weldability and properties of martensitic/austenitic stainless steel joints

Abstract

A series of studies has been carried out to examine the weldability and properties of dissimilar steel joints using martensitic and austenitic stainless steels F6NM (OCr13Ni4Mo) and AISI 347, respectively. This type of joint requires good mechanical properties, corrosion resistance, and a stable magnetic permeability in addition to a good weldability. Weldability tests include weld thermal simulation of the martensitic steel to investigate the influence of weld thermal cycles and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of the heat affected zone (HAZ); implant testing to examine the tendency for cold cracking of martensitic steel; and rigid restraint testing to determine hot crack susceptibility of the multipass dissimilar steel joints. The simulation results indicated that the toughness of the martensitic steel HAZ did not change significantly after the weld thermal cycles. The implant test results indicated that welds produced using nickel based filler show no tendency for cold cracking, whereas welds produced using martensitic or ferritic filler show such a tendency. Based on the weldability tests, a welding procedure (tungsten inert gas welding for root passes with HNiCrMo-2B wire followed by manual metal arc welding using ENiCrFe-3B coated electrode) was developed and a PWHT at 600°C for 2 h was recommended. Joints produced using the developed welding procedure are not susceptible to hot and cold cracking. After PWHT the joints exhibit both satisfactory mechanical properties and stress corrosion cracking resistance.

MST/1955