Mechanical Properties Of Welded Joints Research Articles

Microstructure and mechanical properties of 2A12 aluminum alloy welded joint through CMT double side welding

In this work, the cold metal transfer (CMT) double side welding was carried out to weld 2A12 aluminum alloy plate. The influence of the heat input on the weld appearance was studied, which indicated that when the heat input was exceeded to 651.75 J/mm the better weld appearance was obtained. Through the scanning electron microscope (SEM), electron back-scatter diffraction (EBSD) and tensile testing, the microstructure and mechanical properties of welded joints were investigated. The results showed that the size of microstructure in the front weld seam was less than that of the back weld seam due to the secondary thermal cycle. With the increases of heat input, the average grain size and elongation of welded joints were increased, the tensile strength of welded joints was reduced. The strength coefficient of welded joint was about 70%. The fracture model of welded joint belonged to ductile fracture.

Study on the weld formation, microstructure and mechanical properties of AZ31B Mg alloy in AC/DC mixed gas tungsten arc welding process

In this work, a new welding electrical signal waveform of the AC/DC mixed waveform is purposed to improve the welding quality of magnesium alloy TIG. The method is named as AC/DC mixed tungsten inert gas arc (MIX-TIG) welding. The AZ31B Mg alloy welded joints were obtained by AC-TIG and MIX-TIG. Through investigation of the weld formation, microstructure and mechanical properties of welded joints, the results showed that when the welding current of 90A∼110 A, the completely penetration of welded joints could be obtained. There was no obvious difference for the geometrical parameters of the weld cross-section between the AC-TIG and MIX-TIG. The microstrcuture of fusion zone consisted of α-Mg matric and β-Mg17Al12 phase. At the same welding conditions, the average grain size and β phase number in the MIX-TIG were less than that of the AC-TIG. The microhardness of the AC-TIG fusion zone was slightly larger than that of the MIX-TIG owing to the increase of β phase number. The strain of the AC-TIG welded joint was reduced by approximately 24% compared with that of the MIX-TIG welded joint.

Effect of preheat & post-weld heat treatment on the microstructure and mechanical properties of 6061-T6 aluminum alloy welded sheets

MIG welding is one of the most predominantly welding techniques in manufactories due to its high automation. However, aluminum alloy welded joints fabricated using MIG welding often exhibit a reduction in mechanical properties. In this paper, an attempt has been made to combine preheat and post-weld aging treatment in double-pulse MIG (DP-MIG) welding process to produce 6061-T6 aluminum alloy welded sheets with high mechanical properties. Response surface methodology (RSM) was used to study the main effect and interactive effect of heat treatment parameters including preheat temperature, aging temperature and time on mechanical properties. On this basis, the optimum heat treat parameters that maximize both strength and ductility of welded joints have been determined using multi-objective optimization algorithm. Additionally, the influence of heat treatment parameters on the microstructural evolution and mechanical properties of welded joints was further investigated, by systematic experimental and theoretical analysis. The results showed the preheat temperature affects the grain size and precipitation of the welded joint, while the aging heat treatment mainly affects the precipitation and transformation of the strengthen phase. Since the aging temperature is of greater significance for the improvement of mechanical properties of welded joints, compared with other heat treatment parameters and their interactions, indicating the strengthening of precipitates determines the mechanical properties of welded joints.

RETRACTED: Influence of rotation speeds on microstructure and mechanical properties of welded joints of friction stir welded AA2014-T6/AA6061-T6 alloys

This study presents the joining process of plates with thickness of 4 mm in AA2014 and AA6061 through Friction Stir Welding (FSW) process under alternative tool rotating speeds. AA2014-T6 and AA 6061-T6 alloys were friction stir welded with cylindrical eased pin tool at different revolving speeds such as 700, 900 and 1100 rpm and constant welding speed of 50 mm/min. Mechanical behavior of the FSW of an aluminum alloy exposes a key role of the microstructure. The microstructure change in the interfacial region is characterized using Optical Microscopy (OM). The average grain size was determined based on ASTM E112 – 12 standards. The mechanical properties like tensile strength, micro hardness, and flexural strength of the dissimilar aluminum alloys were evaluated. The fracture examination of the tensile samples was evaluated using Scanning Electron Microscope (SEM). Distance Amplitude Curve (DAC) shows that no recordable internal discontinuities are observed for all three weldments. Further, the study articulated that the effect of rotational speed (900 rpm) exhibits better hardness, tensile and flexural strength. In addition, there was a significant improvement in the grain structure and the average % of grain structure with an average grain size was found to be 15.6 µm and it directly influences the mechanical properties.

Effect of Transient Thermal Conditions on Columnar-to-Equiaxed Transition during Laser Welding: A Phase-Field Study

The columnar-to-equiaxed transition (CET) is commonly observed in laser welds. It is able to prevent the growth of large columnar grains and consequently improve the mechanical properties of welded joints. In this paper, the CET behaviors at different locations in the laser weld of an Al–Mg alloy are observed experimentally and studied systematically. In order to describe the dynamic CET behaviors, an integrated phase-field (PF) model coupled with transient thermal conditions and a Gaussian heterogeneous nucleation model is developed. Investigations on columnar growth under steady conditions are performed first. In particular, the effects of thermal conditions, i.e., solidification rate and temperature gradient, on the constitutionally undercooled degree and region ahead of the solidification front are quantitatively studied. In a laser weld, it is found that the CET behaviors vary significantly along the thickness direction. Our PF simulation results indicate that the CET depends strongly on the locally transient thermal conditions in the fusion zone. The transient thermal conditions affect CET behaviors by dynamically adjusting the constitutionally undercooled degree and region during the solidification process. The predicted CET behaviors under transient conditions exhibit reasonably good agreements with corresponding experimental results.

Structure and mechanical properties of welded joints of high-strength low-alloy steel for arctic purposes

The work is devoted to the research of cracks causes in welded joints of high­strength steel for arctic purposes based on the study of the structure and mechanical properties of the weld metal and the zone of thermal influence. Consumers of machine­building products make increasingly high demands on welded joints of metal structures. This necessitates the use of rolled steels for their production, which have increased mechanical and special properties. When welding MAGSTRONG W700 type steels, cracks are observed in local sections of welded joints. It was established that the structure of the weld metal of welded joints of MAGSTRONG W700 steel is characterized by the presence of columnar crystals with a hardness of 312 – 323 HV. The metal structure in the overheating area of thermal influence zone is characterized by the presence of enlarged primary grain, as well as batch formations of bainite and bainite-martensite with hardness of 338 – 352 HV. The level of temporary resistance to rupture of the metal in thermal influence zone is 618 – 627 MPa. Depending on the test temperature, values of the impact strength of the metal in thermal influence zone vary from 62 to 86 J/cm2. MAGSTRONG W700 steel has good resistance to the formation of hot cracks during welding (UCS = 20,3), however, it has an increased tendency to form cold cracks (CE = 0,48). Analysis of the data obtained showed that destruction of welded joints of the studied steel occurs due to its unsatisfactory weldability. Such weldability is due to a complex chemical composition, as well as a whole set of factors (such as the formation of unfavorable structures in the metal of welded joints under the influence of thermal welding cycles, a complex picture of welding stresses, the level of which exceeds the temporary resistance to metal rupture). Also, the structure of the weld metal has a large­crystalline structure, which significantly weakens the connection.

Effect of Ultrasonic Vibration on Grain Size and Precipitated Phase Distribution of 6061 Aluminum Alloy Welded Joint

To improve the weldability of 6061 aluminum alloy and improve the mechanical properties of welded joints, ultrasonic was introduced into the welding process. The microstructure changes of welded joints under different ultrasonic power were studied, and their effects on the mechanical properties of welded joints were analyzed. The grain size was calculated, and the distribution of precipitated phases was observed by the EBSD technique. The results show that the cavitation and acoustic flow produced by ultrasonic vibration can refine the microstructure of welded joint, reduce the grain size by nearly 50%. It promotes the transition of alloy elements to weld and eliminates the segregation of the strengthening phase to the grain boundary, thus improving the mechanical properties of the welded joint.

Microstructure and Eddy-Current Analysis of Aluminum 01570 Welded Joints Obtained by Friction Stir Welding

The article presents the results of studies of aluminum alloys connected by a welded joint obtained by friction stir welding. During this kind of welding a recrystallized fine-grained microstructure is formed in the joint. The pictures of the weld area microstructure are presented, and the eddy current probe signal variations when scanning the joint are shown. The resulting parameter of the eddy current probe was the local electrical conductivity of the weld area. It is demonstrated that the average grain size of the welded joint microstructure varies in the area of weld defects, which was determined by the signal variation of the eddy current probe. The microstructure peculiarities formed in the weld area where the defects are located, and their influence on the mechanical properties of welded joints are discussed. The results of a series of experiments allow concluding about the qualitative characteristics of the obtained welded joints.

Effect of S-curve laser power for power distribution control on laser oscillating welding of 5A06 aluminum alloy

Laser oscillating welding of 5A06 aluminum alloy is widely used in industry. In order to improve the performance of Al-based welded joints and reduce welding defects, this paper details the effects of employing an S-curve laser power which is distributed along the laser oscillating path (sine wave) to improve the microstructure and mechanical properties of the joints. By applying the S-curve and an equal power condition to the 5A06 aluminum alloy, bottom butt sinusoidal path laser oscillating welding was performed. The welding appearance, microstructure and mechanical properties of the welded joints under two laser oscillating welding processes were investigated. Our results showed that laser oscillating welding using the S-curve power allows to obtain good joints when compared to the joints produced with constant power. When the linearly varying laser power of “high-low-high” applied periodically was employed, the grains in the joint structure showed the cyclic “growth-inhibition-growth” phenomenon. This growth mechanism not only refined the grain structure, but also narrowed the columnar region, and improved the mechanical properties of the joint. Compared with the laser oscillating process with constant power, the tensile strength of the joints using the S-curve power was increased by 35.3 %. Moreover, the tensile strength of the welded test coupons with S-curve power was 337 MPa, which is about 99.1% of the base metal (340 MPa). The welded joints using the S-curve power showed larger and deeper dimples, highlighting higher ductility and good plasticity. This paper provides a new approach for the research of laser oscillating welding and the control of laser power to improve the mechanical properties of welded joints.

Comparison Study on Welding Temperature and Joint Characteristics of AZ31 Magnesium Alloy by Ultrasonic and Heat Pipe Assisted FSW

As an important factor in friction stir welding (FSW) process, temperature directly affects the microstructures and mechanical properties of welded joints. The present work aims to investigate the welding temperature and joint characteristics of AZ31 magnesium alloy under three FSW conditions: conventional friction stir welding (FSW), ultrasonic assisted friction stir welding (UaFSW), and ultrasonic and heat pipe assisted friction stir welding (UHaFSW), respectively. The results show that the welding temperature distributions and the characteristic of “non-uniformity” are presented in the FSW and UaFSW joints along the welding and horizontal directions. Compared with conventional FSW, UaFSW can effectively balance and improve the non-uniform temperature distribution in the joints, resulting in the significant decreases in the peak temperatures and durations of high temperature. Hence, the grains are refined in the microstructure of the nugget zone in the UHaFSW joints, which enhances their microhardness and tensile properties. Based on these results, it can be concluded that UHaFSW could be an effective method to improve the mechanical properties of AZ31 magnesium alloy welded joints.

Investigation on the microstructure and mechanical properties of Ti6Al4V titanium alloy electron beam welding joint

Electron beam welding (EBW) is a fusion joining process particularly suitable for welding titanium plates. In the present work, 2.5 mm thickness Ti6Al4V titanium alloy plates were butt-welded together with backing plates by EBW. The detailed procedures of experiments were used to investigate the microstructure and mechanical properties of welded joints. The optimum welding speed was determined by microstructure examinations, microhardness tests, X-Ray diffraction tests, shear punch tests (SPT) and stress simulation calculations. The results showed that all microstructure of welded metal (WM) was martensite phase under the different welding speeds. In the heat-affected zone (HAZ), the martensite phase gradually evolved to be small and equiaxed. It can be seen that the microstructure of each region in welded joints did not change significantly. When the welding speed is between 8 mm/s and 14 mm/s, it can be seen from the macroscopic appearance of the joints that there was no utterly fused penetration between the butt plate and substrate. Finite element simulation was carried out for the no-penetration depth under different welding conditions, and it was found that the stress suffered by the small no-penetration depth was the smallest. Using different welding parameters shows that the engineering stress in WM was higher than other areas, and BM was the lowest. As welding speed increases from 8 mm/s to 14 mm/s, the variation of microhardness distribution was not evident.

Effect of friction stir welding modes on welds quality of aluminum 1939T1 alloy and mechanical properties of welded joints

The results of effect of friction stir welding on the quality of the resulting welded joins of aluminum 1939T1 alloy, the formation of defects, as well as the mechanical properties of welded joints are presented. Recommendations are given on the choice of friction stir welding parameters that allow obtaining butt joints of plates with thickness of 10 mm made of 1939T1 alloy with strength coefficient of the welded joint at the level of 0.96 of the ultimate tensile strength of the base metal.

Influence of reinforcement on weld bead characteristics of friction stir processed Al5083/NFA composite

Aluminum 5083 alloy has been reinforced with nano fly ash (NFA) through the friction stir processing (FSP) route to fabricate the Al5083/NFA composite. Grooves are machined with different dimensions on the Al5083 alloy plates to incorporate nano fly ash and fabricate composites carried by one pass FSP. Composites with 1, 2 and 3% wt. of NFA as reinforcement material are fabricated and the weld joints of the composites are obtained by friction stir welding (FSW). Tool rotational speeds of 1200 rpm, 1400 rpm, and 50 mm/min traverse speed are considered as FSW process parameters. The increased addition of NFA influences the mechanical properties of weld joints, and increased tensile strength and hardness were observed. It was concluded that NFA particles were most effective for improving the mechanical properties of the AMC weld beads.

Stress corrosion cracking of friction stir welded AISI 304 and 316 L dissimilar steel alloys

This study investigated the corrosion and SCC susceptibility of Friction stir welded AISI 304 and 316L similar and dissimilar stainless steel. In Fusion welding process (SMAW, GMAW, and GTAW) high temperatures are used, because of high operating temperature the heavy residual stress led to the severe cracking in the weldments. To overcome these problems, low operating temperature friction stir welding (FSW) technique was employed to fabricate stainless steel joints. Microstructural analysis has been made using optical microscopy (OM) and SEM. Tensile test was carried out to evaluate the mechanical properties of weld joints. Mechanical result indicates that the ultimate tensile strength of welded metal is higher than the base metal. Based on this study to draw conclusions and give recommendations for best practice in assessing susceptibility to SCC to pulp and paper mills.

Inicijacija i rast prsline u zavarenom spoju čelika za rad na povišenim temperaturama

In a paper given, experimental investigations have included the analysis of crack initiation and growth in welded joint of steel for operation at elevated temperatures. For better understanding of the phenomenon of crack initiation and propagation in welded joints of A-204 Gr. A steel, designed for high-temperature and high-pressure application, it is necessary to determine the effect of heterogeneity of microstructural and mechanical properties on fracture toughness and fatigue crack initiation and propagation in welded components. Based on the tests conducted with pre-cracked CT and Charpy size specimens, the effect of heterogeneity of microstructural and mechanical properties of welded joints on fracture toughness and fatigue-crack growth parameters was determined.

Effect of Heat Input on LMHMW Joint of Carbon Steel

Laser-MIG hybrid multi-layer welding (LMHMW) technology has been employed in paraxial configuration with laser leading for the welding of 20 mm thick Q235 carbon steel plates to exploit the hybridization effect that addresses the shortcomings of the individual process as well as to compliment their merits. The bilateral effects of arc augmented laser welding have resulted in complete joint penetration, process efficiency, stability and gap bridge ability. Samples welded under varying heat inputs in multiple passes have been analyzed for their microstructure evaluation using an optical microscope followed by tensile and Vickers hardness testing in various regions of the weld zones. This process was conducted to characterize the effect of heat input on the mechanical properties of the welded joints. The experimental results illustrate that different heat inputs have significant effects on the microstructure, heat affected zone width and mechanical properties of welded joints. The microhardness near the fusion line decreases dramatically due to the influence of the phase transformation process, and the highest microhardness value is obtained in the center of the weld seam. By using reasonable process parameters, the strength of the welded joint can obtain 458.5 MPa.

Influence of twin-wire welding on the microstructure and properties of structural steel

Increasing efficiency and avoidance of overheating materials is relevant in welding manufacturing. There is a need to find the optimal balance between these two aspects.In response, this manuscript reports the replacement of one-wire method with two-wire in GMAW process. The mechanical properties of welded joints do not differ, except for the impact toughness of the welds, which is slightly lower in the welded joint using the twin-wire method, which corresponds to the higher grain boundary ferrite and sideplate ferrite volume fraction in the weld. The use of the twin-wire method shortened the arc burning time by almost 40%.

Features of Acoustic Emission in Tensile Testing of Dissimilar Welded Joints of Pearlitic and Austenitic Steels

This paper presents a study of acoustic emission (AE) during the deformation of dissimilar welded joints of austenitic steel to pearlitic steel. One of the specific problems in these welded joints is the presence of decarburized and carbide diffusion interlayers, which intensively increase in width during long-term high-temperature operation. The presence of wide interlayers negatively affects the mechanical properties of welded joints. Moreover, welded defects are difficult to diagnose in welded joints containing interlayers: due to the high structural heterogeneity, interlayers create structural noises that can hinder the detection of defects such as cracks, pores, or a lack of penetration. The AE method may become a complex decision for diagnosing dissimilar welded joints due to applicability to the testing of heterogenic materials with a complex microstructure. Specimens cut from dissimilar welded joints of austenitic steel to pearlitic steel were tested by tension to rupture, with parallel AE data registration. According to the research results, the characteristic features of the AE were revealed for specimens containing defects in the form of lack of penetration as well as for specimens with diffusion interlayers. The results obtained show that the AE method can be used to test both typical welding defects and diffusion interlayers in welded joints of steels of different structural classes.

Laser beam welding of AlCoCrFeNi2.1 eutectic high-entropy alloy

To determine the potential of an AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) as a structural material, its laser beam welding (LBW) performance was evaluated, and the microstructure and mechanical properties of weld joint were studied. A fully penetrated, defect-free joint was obtained, in which the fusion zone (FZ) exhibited a eutectic lamellar microstructure containing FCC(L12)/BCC(B2) solid solution phases. The FZ contained refined columnar grains, which grown with the preferential 〈111〉 orientation induced by the rapid cooling during LBW. The tensile strength of the FZ was superior than that of the base metal (BM), which was attributed to grain refinement and higher dislocation density. LBW is a suitable process for joining AlCoCrFeNi2.1 EHEAs.

Study of Material Flow and Mechanical Properties of Friction Stir Welded AA2024 with AA7075 Dissimilar Alloys using Top-Half-Threaded Pin Tool

This research work was aimed at evaluating the material flow behavior and mechanical properties of dissimilar aluminum alloys (2024 and 7075) joints prepared by friction stir welding using a tool with top-half-threaded pin. Macro and microstructural study for material flow investigation was carried out. Whereas mechanical properties of welded joints are examined using tensile and micro-Vicker's hardness tests. Zeiss EVO 18 SEM was used for the fractographic study. Average grain sizes were determined at various weld regions. The effect of grain size with the hardness and strength has been discussed. The results demonstrate that the thread's location on the pin significantly affects the flow of the material. The area where the material has been severely plasticized and moved was located at the weld root. Hence welding root defects like void, pinhole, insufficient filling, etc. are avoided. The tensile strength of friction stir welded joint was 312.7 MPa, equivalent to the joint efficiency of 66.5 %. HIGHLIGHTS The threaded pin tool pushed the soft material downwards hence avoiding root defects. The onion ring structure formation has been observed The tool pin is responsible for creating two separate regions at weld line: Low flow region at the top and high flow region at central areas The maximum tensile strength obtain is 312.7 MPa and 66.5 % joint efficiency GRAPHICAL ABSTRACT