Weld Mechanical Properties Research Articles

CNTs distribution and ductility improvement mechanisms in oscillating laser-arc hybrid welding of AZ31B magnesium alloy

Oscillating laser-arc hybrid welding of AZ31B magnesium alloy with different content of carbon nanotubes (CNTs) was carried out, the distribution characteristics of CNTs and its effect on microstructure and tensile properties were investigated. The results showed that the CNTs can increase the absorption rate of the Mg alloy to the laser. Compared with the weld without CNTs, the grain sizes of the welds with CNTs were refined by more than 50 % and the maximum intensities of {0001} texture were weakened by more than 60 %. The mechanical properties of welds were mainly related to the distribution characteristics of CNTs. The tensile strength and elongation rate of the weld employing 3 wt% CNTs ethanol dispersion reached the maximum value of 244 MPa and 12.5 %. Finally, the distribution and ductility improvement mechanism of CNTs were discussed basing on the viscosity of molten pool and the bonding between the CNTs with the matrix.

Microstructure and Mechanical Properties of Arc Zone and Laser Zone of TC4 Titanium Alloy Laser–TIG Hybrid Welded Joint

As a high-efficiency and high-quality welding technology, laser-tungsten inert gas (laser–TIG) hybrid welding has been widely used in the aerospace and marine equipment industries. Through laser–TIG hybrid welding of TC4 titanium alloy, the effect of the current on the weld formation, the microstructure and mechanical properties of the arc zone, and the laser zone was studied. The results show that the molten pool in the arc zone will flow periodically, and the flow becomes more intense with an increase in the current, which will result in a finer grain size in the arc zone than in the laser zone, having the effect of eliminating pores. The spacing of the α′ martensite beams in the laser zone is narrower, with an average spacing of 0.41 μm. The β phase increases gradually with the increase in the current, which will lead to a downward trend in the average hardness of both zones. The average hardness value of the laser zone, containing more α′ martensite and less β phase, is slightly higher than that of the arc zone. The hardness uniformity of the laser zone is also significantly better than that of the arc zone. The tensile strength of the joint shows a trend of increasing first and then decreasing, and the joint with I = 50 A presented the highest tensile strength of 957.3 MPa, approaching 100% of the base metal, and fractured in the fusion zone.

Microstructure homogeneity and mechanical properties of laser-arc hybrid welded AZ31B magnesium alloy

Laser-arc hybrid welding of AZ31B magnesium alloy was carried out, the effects of welding parameters on weld formation, microstructure homogeneity and mechanical properties were investigated. The results showed that laser-arc hybrid welding was beneficial to improve the weld formation of magnesium alloy by inhibiting the defect of undercut and pores. The weld microstructure was mainly columnar grains neighboring the fusion line and equiaxed grains at the weld center. It was interesting that the grain size at the upper arc zone was smaller than that at the lower laser zone, with the difference mainly affected by laser power rather than welding current and welding speed. The welding parameters were optimized as laser power of 3.5 kW, welding current of 100 A and welding speed of 1.5 m/min. In this case, the weld was free of undercut and pores, and the tensile strength and elongation rate reached 252 MPa and 11.2%, respectively. Finally, the microstructure homogeneity was illustrated according to the heat distribution, and the evolution law of tensile properties was discussed basing on the weld formation and microstructure characteristics.

Comparisons of laser and laser-arc hybrid welded carbon steel with beam oscillation

Laser welding and laser-arc hybrid welding of Q235 steel with and without beam oscillation were carried out, the weld formation, microstructure and mechanical properties were investigated. It was found that the width of the heat affected zone (HAZ) increased by beam oscillation during laser welding, while decreased during laser-arc hybrid welding. The side-plate ferrite (FS) increased by the beam oscillation, while the blocky ferrite (FB) was broken up and the proeutectoid ferrite (FP) was reduced. Moreover, the beam oscillation was beneficial to improve the elongation rate from 6.8% to 7.6% for laser welds and 8.3% to 9.8% for hybrid welds, while decrease the micro-hardness of the welds by 85 HV10 for the laser welds and 10 HV10 for the hybrid welds. Finally, the variation in width of HAZ was illustrated according to the heat distribution of the laser source, arc column and oscillating behavior of the laser beam. The relation between microstructure and mechanical properties was established, according to the stirring effect of the oscillated laser beam within the molten pool, and the solidification theories.

Effect of ultrasonic vibration characteristics on mechanical properties of stainless steel laser weld

The laser welding efficiency of stainless steel is high, but the welding quality is still insufficient. In order to improve the welding performance of stainless steel, a controllable ultrasonic laser welding system was designed in the paper. Through numerical simulation and experimental test, the influences of ultrasonic vibration on the mechanical properties of weld were obtained. For the simulation study, the sound vibration coupling scheme was applied to the welding model. The closed environment model was established, and the characteristic frequency and sound pressure distribution of ultrasonic were simulated and analyzed by COMSOL software. In the aspect of performance test, through the real-time monitoring of the welding system, the effect of ultrasonic on the molten pool area, molten pool flow rate and metal vapor pressure is obtained. Under different ultrasonic excitation frequencies, the changes of weld microstructure, wear morphology, hardness and oxidation were studied. The results show that ultrasonic vibration can significantly improve the wear resistance, hardness and corrosion resistance of stainless steel welds. The ultrasonic energy efficiency at the second-order characteristic frequency is higher, the flow rate in the molten pool is low, and the joint quality is better.

Enhancing the joint of dissimilar aluminum alloys through MIG welding approach assisted by ultrasonic frequency pulse

In this work, AlSi10MgMn die cast aluminum alloy and 6061 aluminum alloys were bonded using Metal inert gas (MIG) welding assisted by ultrasonic frequency pulse (UFP). The effect of UFP on the weld shape, joint porosity, microstructure and mechanical properties of the joints was investigated. Results revealed a distinct decrease in joint hydrogen porosity defects and pore size via the UFP-MIG welding approach in comparison to a directly bonded joint. This method resulted in the tensile strength of the joint reaching 185% of the joint bonded without UFP. The regulating mechanism of UFP on the joint porosity was determined.

Mechanism of the Influence of Weld Pool Wall Constraint on Weld Profile Formation in Gas Metal Arc Welding of Aluminum Alloy

This paper aims to clarify the influence of the wall constraint on the convection behavior of molten metal in a molten pool and improve the weld formation and mechanical property. In this paper, the flow behavior of molten metal under the action of weld pool wall constraint and driving forces is studied; especially, the mechanism of weld pool wall constraint on the flow behavior of molten metal and its influence on the weld formation are studied and verified. Additionally, the influence of convection behavior on the composition distribution and properties of weld are explored. The results show that the bottom wall of the molten pool has the function of constraint on the molten metal, which directly determines the profile and size of the upper and lower reinforcement of the weld. Therefore, the reinforcement forming coefficient Rc is proposed to value the diversion ability of the bottom wall. Meanwhile, the EDS results demonstrate that the flow pattern of molten metal has a significant effect on the distribution of the weld composition for different profiles of weld. For the weld with depressed upper reinforcement, its mechanical properties can be significantly improved because of its enhanced wall constraint when the supporting plate is added.

Effect of Porosity on the Thermo-Mechanical Behavior of Friction-Stir-Welded Spark-Plasma-Sintered Aluminum Matrix Composites with Bimodal Micro- and Nano-Sized Reinforcing Al2O3 Particles

The thermo-mechanical behavior of nanosized Al2O3 particles reinforcing aluminum was analyzed in the present paper. The material was prepared by spark plasma sintering and friction stir welding. The thermal stresses affecting the composite behavior during welding were modeled through COMSOL MultiPhysics, and the results were validated by the analyses of the composites’ mechanical properties. The spark-plasma-sintered materials presented limited porosity, which was taken into account during the modeling phase. Both model and experiments revealed that higher heat input is related to better material mixing during welding and sound mechanical properties. Thermal stresses lead to residual stresses close to 300 MPa in the thermo-mechanically affected zone for processing conditions of 1900 RPM and 37 mm/min. This leads to an increase in hardness up to 72 HV.

Weldability of Nickel/Aluminum Dissimilar Materials Laser Welding Part I: Microstructure Development, Solidification Behavior and Mechanical Properties of Polycrystalline Nickel-based Superalloy

Weldability-related issues, including asymmetrical weld pool shape, γ phase multicomponent microstructure development, solidification behavior and mechanical properties, of γʹʹ precipitation-strengthened polycrystalline nickel-based superalloy are experimentally analyzed during keyhole laser welding repair. The crucial relationship between them provides weldability improvement opportunities and defect-free high quality weld for feasible aerospace materials laser processing. Attractive neck transition region of weld is more vulnerable to coarser dendrite than bottom part in the vicinity of fusion boundary, and this location is also liable to abundant Laves/γ eutectic phase formation because of heat and solute accumulation. The dominant chemical inhomogeneity brings about microstructure anomalies and irregular morphology to deteriorate hot cracking resistance. Because of thermometallurgical factors of selective alloying partition in the molten pool, partition-resistant Cr is chemically accumulated in dendrite core, while partition-susceptible Ti, Al, Mo and Nb are enriched in high-supersaturation interdendrite region, which consequently result in serious segregation and extensive Nb-rich intermetallic phase formation across solidification interface. Dendrite refinement and aggressive Laves/γ eutectic phase formation suppression are not simultaneously satisfied by low heat input under nonequilibrium solidification conditions. Therefore, mechanical properties are only partially improved by diffusion-limited microstructure refinement as result of phase instability. In other words, reductions of tensile strength and ductility are attributed to brittle Laves/γ eutectic phase formation during terminal stage of solidification. The severity of eutectic reaction thermodynamically depends on nail-shaped keyhole profile, solidification conditions and solute redistribution ahead of solid/liquid interface. Additionally, viable control of weld metallurgical and mechanical properties progressively encourages optimal combination of laser power and welding speed to interdendritically minimize disadvantages of eutectic phase formation by a variety of welding conditions optimization.

Effect of Temperature and Material Flow Gradients on Mechanical Performances of Friction Stir Welded AA6082-T6 Joints.

The temperature and material flow gradients along the thick section of the weld seriously affect the welding efficiency of friction stir welding in medium-thick plates. Here, the effects of different gradients obtained by the two pins on the weld formation, microstructure, and mechanical properties were compared. The results indicated that the large-tip pin increases heat input and material flow at the bottom, reducing the gradient along the thickness. The large-tip pin increases the welding speed of defect-free joints from 100 mm/min to 500 mm/min compared to the small-tip pin. The ultimate tensile strength and elongation of the joint reached 247 MPa and 8.7%, equal to 80% and 65% of the base metal, respectively. Therefore, reducing the temperature and material flow gradients along the thickness by designing the pin structure is proved to be the key to improving the welding efficiency for thick plates.

Microstructure and mechanical properties of gas metal arc welded CoCrFeMnNi joints using a 308 stainless steel filler metal

In this paper, gas metal arc welding of a CoCrFeMnNi high entropy alloy was performed using 308 stainless steel filler wire. Electron backscatter diffraction and synchrotron X-ray diffraction were used to determine the microstructural evolution, while microhardness mapping and non-contact digital image correlation were employed to assess the local mechanical response across the welded joints. Further, thermodynamic calculations were implemented to support the understanding of the microstructure evolution. Through a systematic analysis of the microstructure evolution and mechanical properties, it is established a correlation between welding process, microstructure and mechanical properties. Besides, this work lays the foundations for the use of low-cost arc-based welding technologies for successful joining and application of welded joints based on high entropy alloys.

Effect of fibre laser welding parameters on the microstructure and weld geometry of commercially pure titanium

The primary purpose of the study was the metallurgical characterization of laser welds. The weldability of commercial production of pure titanium and titanium alloy (CP-Ti) has also been examined. In this research, the laser fibre method was used to weld sheets of pure titanium, and then microscopy and scanning electron microscopy were used to study the changes in the microstructure, the depth of weld penetration and the width of the weld area with changing welding parameters. The results proved that increasing the laser power significantly increases the depth of weld penetration and weld width. When the heat input is increased, the shape of the weld pool changes from a V shape to an hourglass shape. It was also observed that the depth of the crater formed increases with the increase in the laser power due to the increase in the melting and evaporation of the weld metal. Increasing the welding speed also has a negative impact on the weld geometry because it reduces the heat input and absorption of laser energy by the weld metal and thus reduces the melting of the metal. The microstructure of the fusion zone consists of acicular α. Fine grains formed in the weld centre at low heat input; the granules became columnar-like. Since commercially pure titanium contains a small amount of beta-phase stabilizers, the cooling rate is extremely high for martensite to occur. In the future, it is recommended to study the effect of changing welding parameters on the mechanical properties of pure titanium because of its great importance in industrial and medical applications. Studying the effect of changing laser power and welding speed on the metallurgical properties of pure titanium, and consequently its effect on the mechanical properties of welds.

Refined weld microstructure and enhanced joint mechanical property of 1460 Al-Li alloys via double-pulsed variable polarity TIG arc welding

In this work, 1460 Al-Li alloy plates (thickness 2 mm) were butt-welded by using conventional variable polarity TIG welding (VPTIG), low-frequency pulsed (2 Hz) variable polarity TIG welding (P-VPTIG), and double-frequency (low-frequency (2 Hz) + ultrasonic-frequency (20 kHz)) pulsed variable polarity TIG welding (DP-VPTIG). The influences of the three current modes on the weld microstructure and mechanical properties were investigated contrastively. Weld microstructure was characterized by a metallographic optical microscope, scanning electron microscope, and electron backscattering diffraction technology. The mechanical properties of those 1460 Al-Li alloy-based joints were measured by microhardness and room-temperature uniaxial tensile test. Obtained results indicated that modulating pulsed current on the conventional VPTIG current can effectively eliminate the coarse columnar structures, resulting in whole refined equiaxed grains in the weld zone (WZ) and fusion zone (FZ). By comparison, DP-VPTIG current exhibited the most prominent effect of homogenization and refinement on the weld microstructure. In addition, it significantly increased the quantity and width of the fine strip-like equiaxed grain zone. The eutectic phase particles distributed in the grain boundaries were refined prominently by the modulation of pulsed current. Compared with the VPTIG process, both P-VPTIG and DP-VPTIG processes effectively enhanced the strength and elongation of 1460 Al-Li alloy-based joints, with an increase of 6.2 % and 10.9 % in tensile strength and 16 % and 128.6 % improvement in elongation, respectively.

Indentifying the effect of micro friction stir spot welding (µFSSW) parameters on weld geometry, mechanical properties, and metallography on dissimilar materials of AZ31B and AA1100

Micro-friction stir spot welding (µFSSW) is one type of welding that is suitable for joining lightweight materials. One of the challenges in joining lightweight materials with µFSSW is that the material is easily perforated, or the join is not strong enough, so it is necessary to select the right µFSSW parameters. In this article discusses about investigates the micro-Friction Stir Spot Welding (µFSSW) parameters on weld geometry, mechanical properties, and metallography on dissimilar materials of AZ31B and AA1100. The material thickness of the AZ31B and AA100 is 0.5 mm and 0.32 mm, respectively. The µFSSW tool is made of high-speed steel (HSS) with a pin diameter of 0.25 mm and a shoulder diameter of 0.5 mm. The constant process parameters of the µFSSW joint used, i. e., plunge depth, dwell time plunge rate, and high tool rotational speed of 33,000 rpm. Welding test results include weld geometry, mechanical properties, and metallography. Weld geometry testing to determine the weld nugget diameter. The mechanical properties test was shear tensile test and cross tensile test, while the metallographic test included macrostructure and microstructure observations. The results of the FSSW weld geometry show that at a dwell time of 700 milliseconds and a plunge depth of 600 microns, the weld pin diameter and weld shoulder diameter are close to the pin diameter and the diameter of the shoulder tool used. Dwell time and plunge depth has a significant effect on tensile strength. The maximum shear and cross loads achieved were 387±17 N and 29±2 N, respectively. Intermetallic compounds (IMC) are observed at the interface of the two materials, while a dwell time of 700 milliseconds give the effect of cracks on the inside of the weld

Investigation of thermal influence on weld microstructure and mechanical properties in wire and arc additive manufacturing of steels

Alloy steels are commonly used in many industrial and consumer products to take advantage of their strength, ductility, and toughness properties. In addition, their machinability and weldability performance make alloy steels suitable for a range of manufacturing operations. The advent of additive manufacturing technologies, such as wire and arc additive manufacturing (WAAM), has enabled welding of alloy steels into complex and customized near net-shape products. However, the functional reliability of as-built WAAM products is often uncertain due to a lack of understanding of the effects of process parameters on the material microstructure and mechanical properties that develop during welding, primarily driven by thermal phenomena. This study investigated the influence of thermal phenomena in WAAM on the microstructure and mechanical properties of two alloy steels (G4Si1, a mild steel, and AM70, a high-strength, low-alloy steel). The interrelationships between process parameters, heating and cooling cycles of the welded part, and the resultant microstructure and mechanical properties were characterized. The welded part experienced multiple reheating cycles, a consequence of the layer-by-layer manufacturing approach. Thus, high temperature gradients at the start of the weld formed fine grain structure, while coarser grains were formed as the height of the part increases and the temperature gradient decreased. Microstructural analysis identified the presence of acicular ferrite and equiaxed ferrite structures in G4Si1 welds, as well as a small volume fraction of pearlite along the ferrite grain boundaries. Analysis of AM70 welds found acicular ferrite, martensite, and bainite structures. Mechanical testing for both materials found that the hardness of the material decreased with the increase in the height of the welded part as a result of the decrease in the temperature gradient and cooling rate. In addition, higher hardness and yield strength, and lower elongation at failure was observed for parts printed using process parameters with lower energy input. The findings from this work can support automated process parameter tuning to control thermal phenomena during welding and, in turn, control the microstructure and mechanical properties of printed parts.

Microstructure and mechanical performance of dissimilar friction stir spot welded AA2024-O/AA6061-T6 sheets: Effects of tool rotation speed and pin geometry

Nowadays, friction stir spot welding (FSSW) is becoming a serious candidate technology to join aircraft materials such as AA2024-O and AA6061-T6 since the use of FSSW offers significant weight savings compared to a conventional riveting technique. However, some issues, especially related to mechanical properties of FSSW joints still exist. To address these problems, the present investigation aims to study effects of tool rotation speed and pin geometry on microstructure and mechanical strength of dissimilar friction stir spot welded AA2024-O/AA6061-T6 joints. The welding processes were conducted using two different tool pins, namely cylindrical and stepped pins at varying tool rotation speeds of 900 rpm, 1400 rpm and 1800 rpm. Subsequently, experimental works including microstructural observation, microhardness measurements, lap shear tests combined with fractography analysis were conducted. Results showed that an increase in tool rotation speed resulted in microstructural coarsening in stir zone (SZ). In addition, the tool rotation speed together with the pin affected the material flow hence hook characteristics. It was found that the dissimilar friction stir spot AA2024-O/AA6061-T6 welded joint having excellent lap shear failure load (LSFL), typically 4468.4 N was produced using a cylindrical pin at the tool rotation speed of 1400 rpm. Under this lap shear testing, the mode of failure changed from shear to mixed mode failure as the tool rotation speed was increased. It seemed that hook characteristics, grain size and precipitation hardening were the key factors influencing the weld mechanical properties.

Microstructure and Mechanical Properties of Laser Welded Magnesium Alloy/Steel Joint Using Cu-Si Composite Interlayer

In this study, Cu-Si composite powder was used as the interlayer to carry out laser lap deep penetration welding of AZ31B magnesium alloy and DP590 dual-phase steel. The effects of Cu-Si composite powder on the weld formation, microstructure, and mechanical properties of magnesium alloy and steel joint were studied. The results show that the addition of Si can improve the laser absorption rate of the interlayer and increase the melting depth at the magnesium side. In addition, the Cu-Si composite interlayer hindered the diffusion of Al, and reduced the thickness of reactive layer at the magnesium alloy and the steel interface. After adding Si into the interlayer, the reactive layer changed from Fe3Al+α-Mg to Fe-(Al, Si) +α-Mg and the content of intermetallic compounds in the reactive layer decreased, which improved the plastic deformation capacity and the ductility of the reactive layer. As a result, the tensile shear force firstly increased and then decreased with the Si increase. The maximum tensile shear force of 86.2 N/mm was achieved when the Si content was 5%, which was 20.4% higher than that of the Cu interlayer. Plus, the fracture location changed from near the steel side to near the magnesium side weld.

Investigation of weld formation and porosity in 5052 aluminium alloy laser-GMA hybrid welding assisted by magnetic field with different orientations

Steady magnetic field with both orientations including longitudinal magnetic field (LMF) and transverse magnetic field (TMF) was used. The influence of LMF and TMF on weld formation, porosity and mechanical property of 5052 aluminium alloy laser-gas metal arc (GMA) hybrid welding was investigated. The shielding effect of hybrid plasmas on laser energy was weakened by TMF, leading to an increase in weld depth under TMF. Porosity rate was significantly reduced to 2.61% under TMF, because keyhole stability was improved, escaping channels for bubbles were increased, and solidification time of molten pool was prolonged. As a result, the highest tensile strength (174.7 MPa) of hybrid weld was obtained at TMF, owing to the lowest porosity rate.

Effect of Tool Design on the Mechanical Properties of Bobbin Friction Stir Welded High-Density Polyethylene Sheets: Experimental Study

Welding polymers by the friction stir welding (FSW) technique is one assembly process among several known assembly techniques which consists in welding two materials without filler material. The FSW process is based on the generation of heat due to friction and material deformation under an axial force. Among the main aspects affecting material flow, the choice of welding tool geometry has become of great interest to improve the welds quality. The main objective of this work is the welding of polymers using the FSW technique. A new method of welding HDPE (high density polyethylene) plates, called BT-FSW (bobbin tool friction stir welding) was developed. Standard rectangular shape intended for the distribution of natural gas has been successfully welded by BT-FSW. Tensile tests and hardness measurements were carried out on samples cut from the welded sheets and the results were analyzed to compare the mechanical characteristics of the plates welded by the BT-FSW and conventional FSW (C-FSW) processes. The results of the comparative studies on the micro-hardness characteristics and mechanical properties of the two welding processes indicate that welding using the bobbin tool can significantly reduce hardness and improve both weld formation and mechanical properties of joints. This study showed that the design of the welding tool has a big impact on the weld strength. An improvement in the mechanical properties of the specimens welded by BT-FSW was observed to give a better welding quality for the polymers studied.

Impact of power modulation on weld appearance and mechanical properties during laser welding of AZ31B magnesium alloy

A new laser welding process with power modulation was proposed to promote the weld formation and improve the quality of welds over magnesium alloys. The impact of the parameters of power modulation on laser welding was investigated experimentally at the aspects of weld formation, keyhole entrance, molten pool flow, and microstructure and mechanical properties of welds. The experiments were performed for the butt joints on AZ31B magnesium alloy sheets with a thickness of 3 mm, and the results shown that the laser welding with a sinusoidal power modulation increased the melting volume and improve the efficiency of energy coupling in comparison with that with a constant power. Power modulation in laser welding could minimize even eliminate the underfill over the top surface of weld. The higher the frequency of power modulation was, the longer the columnar grains formed near the fusion line of weld. With an increase of the amplitude of power modulation, both of the cell grains and columnar grains were decreased in width; while the average size of equiaxed grains was increased. Power modulation in laser welding improved the tensile strength and the elongation of magnesium alloy at welds; when the power was modulated with the frequency of 200 Hz and the amplitude of 300 W, the maximum tensile strength was 237 MPa, and the ultimate elongation was 7.26% and the weld was broken by a mixed ductile–brittle fracture.