Current Tungsten Inert Gas Welding Research Articles

Weld Strength and Cracking Susceptibility Analysis of Pulsed TIG Welded Al-Mg-Si Alloy by Experimental Approach

Aluminium is a non ferrous corrosive resistance metal mainly used in automotive coolers, inter coolers and radiators. They are the part of automobile vehicles and made from aluminium alloys. The joints in this application are created by fusion welding process specifically Tungsten Inert Gas (TIG) and Pulsed current TIG (PCTIG) welding process. The working temperature range of different coolers, radiators are 20° C to 300° C and pressure ranges from 2.5 bar to 3.5 bar. During actual working of coolers, the weld joint experiences sudden high level and low level temperature changes. These will create high thermal stresses in the joints. It leads to cracking in the weld region and create failure of the weld joints. Various factors such as mechanical, metallurgical and thermal are responsible for cracking in the weld joints. Range of solidification temperature is one of metallurgical factor, stress generation is mechanical factor and cooling rate of weld metal is thermal factor for cracking. Houldcroft weldability test is employed to identify the cracking susceptibility (CS) of the weld. The current investigation is intended to discover the effect of pulse TIG welding process parameters on the mechanical properties and cracking susceptibility of precipitated aluminium Al-Mg-Si alloy. Diverse pulsed TIG welding process parameters such as peak current (Ip), base current (Ib) and frequency (f) were investigated with the objective of identify the tensile strength, yield strength and cracking susceptibility. The corresponding findings of optimum parameters are 180 peak current (Ip), 60 A base current (Ib) and at 6 Hz frequency (f) with tensile strength of 185.55 MP, yield strength 156.62 MPa. The significant of each parameter for tensile strength are Ip, Ib, Ip*Ib, Ip*f and Ib*f. The corresponding contributions in % are 14.56, 49.49, 12.26, 5.44, 12.15, 5.04, and 1.05 respectively. The statistical method such as Taguchi was employed for experiment design. Weldability test (Fishbone test) was performed on standard specimen and the cracking susceptibility index was identified. The cracking susceptibility index 5.26 % were observed with the value of 180 A of Ip, 80 A of Ib & 2 Hz of frequency (f).The results give an idea about the effect of pulsed TIG welding parameters on mechanical properties and cracking susceptibility.

Comparative study on CCTIG welding and PCTIG welding of GH4169 under the same heat input

GH4169 is a nickel-based superalloy, but high welding heat input and the harmful precipitates of the Laves phase seriously affect the mechanical properties of the welding joint. In this study, constant current tungsten inert gas welding (CCTIG) and pulsed current tungsten inert gas welding (PCTIG) were used to weld the GH4169 alloy sheet under the same heat input. After welding, the relationship between microstructure and comprehensive mechanical properties was analyzed. According to the results, under the same heat input: (1) The PCTIG welded joint has narrower weld and denser microstructure. (2) The pulse current improved the segregation of Nb element at the weld, and then reduced the precipitation of the Laves phase. (3) Pulse current improved the comprehensive mechanical properties of weld metal. The tensile strength and elongation were increased by 18% and 79% respectively.

Improvement in Depth of Weld Penetration During TIG, Activated-TIG, and Pulsed TIG Welding

Joining of dissimilar materials has gained a lot of interest in the recent years due to the increased demand of high strength and light weight designs. Fusion welding plays a vital role in repairing and manufacturing industries like automobile, construction, ship building, and energy sector. Tungsten inert gas (TIG) welding is more advantageous over other welding processes as it produces high precision welds with aesthetic appearance. The limitation of the process is shallow penetration, distorted and weaker joint formation, and low productivity. In the present work, a critical review and analysis has been done on weld penetration and its enhancement during TIG, activated flux TIG, and pulsed current TIG welding of steels. The purpose of this review is to raise an insight about using the variants of TIG, minimising the energy consumption and heat affected zone while increasing the weld penetration and productivity. Proper selection of welding parameters along with welding speed, electrode diameter, shielding gas, electrode tip angle, arc gap, and flux greatly increase the weld penetration.

Investigation on the Pulsed TIG Welding of Nickel-Base Alloy for Improved Microstructure and Weld Penetration

In this study, a novel pulsed tungsten inert gas (TIG) welding technique that is capable of effectively improving the weldabilities of nickel-based alloys was developed.  The correlation between process parameters and material properties was studied. The effects of ratios of pulse to background welding currents on hardness and penetration in welds and heat-affected zones (HAZs) of Inconel 718 alloy were investigated experimentally by using the pulsed TIG welding technique. It is found that with an increasing ratio of the pulse to background welding current, the hardness in welds increased from 2% to 3.5%, compared to that in constant current TIG welding at the same level of heat input. When the ratio of pulse to background welding current is higher than 6, the penetration in weld was improved significantly by up to 61%. Research work has demonstrated that the pulsed TIG welding technique is an effective approach to control the microstructure and reduce cracking susceptibilities.

Influence of shielding gas on cathode spot behaviours in alternating current tungsten inert gas welding of aluminium

ABSTRACTThe influence of shielding gas (argon, helium) on the cathode spot (CS) behaviours in aluminium AC TIG welding was investigated by the high-speed (500,000 fps) observation. Moreover, the temperature of the weld pool surface was measured by the two-wavelength pyrometer method to discuss its relationship with the CS. Consequently, the average current per CS in the helium case was 16.7 A, higher than 7.6 A in the argon case. The larger current per spot is considered to cause the higher velocity of the CS on liquid surface in the helium case (168 ± 41 m s−1) than that in the argon case. The average number of the CS was almost zero within around a radius of 2.0 mm in helium, which had the temperature above 1300 K.

3D numerical investigation of a free-burning argon arc with metal electrodes using a novel sheath coupling procedure

A novel coupling procedure describing the complicated plasma-electrode interaction process has been developed and applied into the 3D finite volume simulation of a direct current tungsten inert gas welding system. This is achieved by making the space charge layer (sheath) incorporated into the computation domain and interact with both bulk plasma and cathode through the effective electrical conductivity. Both chemical and thermal nonequilibrium phenomena as well as the self-induced magnetic fields have been taken into consideration by the model to ensure a realistic numerical description of a non-thermal arc. The applicability of this coupling procedure is further improved by calculating the real electric potential, which is capable of accounting for the effects of the complicated drift and diffusion processes. Numerical results of both 100 and 200 A discharge currents are presented, field reversal is obtained at near-anode regions in both cases, which is followed by the negative anode sheath potential drop. The region of the strongest electron overpopulation appears at the intersection of plasma fringes and electrode surface. Numerical results of plasma temperature and voltage show good agreement with experimental measurements.

Investigating cathode spot behavior in argon alternating current tungsten inert gas welding of aluminum through experimental observation

The behavior of cathode spots in stationary argon alternating current tungsten inert gas welding of aluminum was clarified in this study. The temporal variation in cathode spot distribution during electrode positive (EP) polarity was, for the first time, revealed quantitatively based on high-speed video camera observation with a frame rate of 500 000 fps. In addition, the weld pool surface temperature at the start and end of EP polarity was also measured using the two-wavelength temperature measurement method to clarify the relationship with the cathode spot behavior. As a result, the general tendency of the life cycle of the cathode spot was clarified. The first cathode spot appeared and divided outside the weld pool. Following this, they moved rapidly toward the weld pool center within 100 µs. After that, the cathode spot group became an uneven and ring-shaped distribution, which expanded outward with time with a velocity of approximately 1 m s−1. The cathode spots have a random movement with the average velocities of each cathode spot on the liquid and solid surface being about 142 ± 59 m s−1 and 87 ± 44 m s−1, respectively. The ratio of the number of cathode spots located in the weld pool to the total number of cathode spots decreased from 100% to 37.4% with elapsed time, except right at the beginning. Furthermore, the temperature of the center surface of the weld pool was 1400 K, and this gradually increased to a slightly higher temperature than the melting point of aluminum around the weld pool boundary at the start of EP polarity. The maximum temperature at the center is considered to be linked with absence of a cathode spot. The temperature at the center decreased by 150 K at the end of EP polarity due to the temporal expansion in the ring-shaped distribution of the cathode spot group leading to a decrease in heat input around the center.

Hot Corrosion Demeanour of Alloy 80A Weldments Fabricated Through Tungsten Inert Gas Welding Technique

In the current study, alloy 80A weldments were produced through tungsten inert gas welding (TIGW) and pulsed current tungsten inert gas welding (PCTIGW) technique using 263 filler wire. Corrosion study was conducted on weldments in both air oxidation environment and molten salt environment under 50 cyclic condition at 900 °C. The results of thermogravimetric analysis showed that corrosion behaviour of weldments obeyed the parabolic rate law of oxidation. Higher weight gain was observed in TIGW under molten salt condition. Less weight was observed in PCTIGW under air oxidation condition. It is inferred that substrates subjected to molten salt environment showed higher weight gain than its respective substrates under air oxidation condition. The existence of Cr2O3, NiO and spinal oxide NiCr2O4 offered good corrosion resistance to substrates. Thus, it was deduced that PCTIG weldments provided good corrosion resistance at high temperature than its respective TIG weldments.

Statistical analysis of tensile strength and elongation of pulse TIG welded titanium alloy joints using Weibull distribution

Abstract In this study, the tensile strength of a pulsed current tungsten inert gas welded Ti-6Al-4 V plate has been statistically analysed by Weibull distribution. Titanium alloy of 1.6 mm thickness was welded with pulsed current tungsten inert gas welding. Testing of mechanical properties was done to understand the influence of pulsing current on the fabricated joint. But the result obtained has to be consistent and repeatable. Hence, this paper investigates a method for predicting the reliability of values obtained for tensile strength and elongation with consistency. The tensile strength results obtained vary between 975 and 1160 MPa and percentage elongation vary between 2.4 and 5.9%. Using Weibull technique in conjunction with the experimental data, we can predict the output more accurately. Using Weibull distribution, the welded joint reliability can be obtained. The probability distribution according to which the joint will fail is estimated with the help of Weibull analysis.

Prediction of optimum weld pool geometry of PCTIG welded titanium alloy using statistical design

Mechanical strength of the weldments is not only influenced by the composition of the metals but selection of process parameters and weld bead profile also play a vital role in determining the strength. The relationships between the process parameters and the bead parameters controlling the bead shape are to be established. This is achieved by the development of mathematical expressions, relating the weld bead dimensions to the important process control variables affecting these dimensions. Also, optimization of the process parameters to control and obtain the required shape and quality of weld beads is also made possible with these expressions. The pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulsed current tungsten inert gas welding (PCTIG) of titanium alloy was analyzed. Box–Behnken design was used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.

Alternative current flux zoned tungsten inert gas welding process for aluminium alloys

A new variant of activating flux tungsten inert gas (TIG) welding process called flux zoned TIG (FZ-TIG) welding is proposed to weld aluminium alloys based on the mechanism of activating flux constricting welding arc. This process can not only increase weld penetration but also obtain perfect weld surface appearance simultaneously. An alternative current FZ-TIG welding is made using SiO2 as the side region material and flux FZ108 developed by the authors with uniform design method as the central region coat material. The weld penetration can reach above three times that of the conventional alternative current TIG welding. All the weld shape, weld microstructure and weld mechanical properties are fine. Except for argon shielding gas flowrate, other welding parameters, including welding current, welding speed, central coat width, central coat content and solvent, have great effect on the weld penetration of alternative current FZ-TIG welding for aluminium alloys.

Prediction and optimization of pulsed current tungsten inert gas welding parameters to attain maximum tensile strength in AZ61A magnesium alloy

Magnesium and its alloys have been considered one of the best materials for automotive applications due its light weight and high strength to weight ratio. Metallurgical advantages of pulsed current tungsten inert gas welding (PCTIG) frequently reported in literature include refinement of fusion zone grain size, reduced width of heat affected zone, etc. In this paper, an attempt has been made to establish an empirical relationship is developed to predict tensile strength of the PCTIG welded AZ61A magnesium alloy by incorporating process parameters such as pulse current, base current, pulse frequency and pulse on time. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the relationships. The developed empirical relationship can be effectively used to predict the tensile strength of PCTIG welded AZ61A magnesium alloy joints at the 95% confidence level. The results indicate that the pulsed current has the greatest influence on tensile strength, followed by pulsed on time, pulse frequency and base current.

Study on Fast-Convert Ultrasonic Frequency Pulse TIG Welding Arc Characteristic

Based on ultrasonic frequency pulse tungsten inert-gas (TIG) welding for 0Cr18Ni9Ti austenitic stainless steel, the influence of pulse level parameters was investigated on the field of arc characteristic and arc force. The experimental results show that the pulse level parameters could have huge impact to arc characteristic and arc force. With the increased frequency of pulse level, arc plasma has a more obvious pinch effect, which causes the enhance of arc voltage. Similarly, the arc force can be improved obviously compared with that during conventional direct current (DC) TIG welding. By contrast, the sensitivity of welding characteristic to pulse current level frequency would reduce while the duty of pulse peak current increased.

EFFECT OF PROCESS PARAMETERS OF PULSED CURRENT TUNGSTEN INERT GAS WELDING ON WELD POOL GEOMETRY OF TITANIUM WELDS

Effect of process parameters of pulsed current tungsten inert gas welding on weld pool geometry of titanium welds M. Balasubramanian ∗ Department of Mechanical Engineering, Velammal Engineering College, Surapet, Anna University, Guindy, Chennai 600 025, Tamilnadu, India V. Jayabalan Department of Manufacturing Engineering, Anna University, Guindy, Chennai 600 025, Tamilnadu, India V. Balasubramanian Centre for Materials Joining & Research, Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar-608 002, Tamilnadu, India Manuscript received 8 July 2009; in revised form 12 April 2010

Thermo-mechanical treatments of Sc- and Mg-modified Al–Cu alloy welds

High-strength heat-treatable aluminum alloy AA2219 finds application in aerospace industries. Though it has good weldability, with alternating current–tungsten inert gas welding, the joint efficiency obtained is only 40%, particularly in thicker plates. In the present study, an attempt has been made to improve the weld metal properties by modifying the chemistry of fusion zone and post-weld thermo-mechanical treatments. Fillers were made through casting route by melting conventional 2319 filler with Sc and Mg. Two levels of Sc (0.3% and 0.6%) and four levels of Mg (0.3% to 0.6%) were varied. Compressive deformation was done on the fusion zone of the weld to get three levels of percentage of reduction (4%, 8%, and 12%). As welded specimens and welds after compressive deformation, those were subjected to post-weld aging treatments at 190oC for different periods up to 100 h. Compressive deformation on the welds made with modified filler of 2319 with Sc and Mg resulted in significant improvement in the weld metal strength.

Influences of pulsed current tungsten inert gas welding parameters on the tensile properties of AA 6061 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. In any structural application of this alloy consideration its weldability is of utmost importance as welding is largely used for joining of structural components. The preferred welding process of aluminium alloy is frequently tungsten inert gas (TIG) 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. Many considerations come into the picture and one need to carefully balance various pulse current parameters to arrive at an optimum combination. Hence, in this investigation an attempt has been made to study the influence of pulsed current TIG welding parameters on tensile properties of AA 6061 aluminium alloy weldments.