Microstructure Of Weld Seam Research Articles

Determination of beam oscillating pattern for tailoring melt flow and microstructural characteristics of laser welded Ti–6Al–4V alloy

The trajectory of beam is highly correlated to the heat distribution and fluid flow within the melting pool in laser welding, which has a great impact on improving the joint microstructure. This study employs fluid simulation techniques to investigate the temperature distribution and flow behavior of Ti–6Al–4V alloy under three laser oscillation welding patterns including none oscillation, sinusoidal oscillation, and circular oscillation, and the optimal oscillating pattern was determined through an analysis of microstructure characteristics. Temperature field simulation results indicate that the oscillation of the beam is efficaciously utilized to diminish the concentrated heat distribution on the base material. Moreover, a manifest difference in energy density and the area of laser action is produced, which leads to variations in the location and depth of the distribution of keyholes. Under circular oscillation, the flow behavior is more pronounced, with peak flow velocity increasing by approximately 80 % compared to none oscillation and new vortices were created in the horizontal section at the end of an oscillation period. Furthermore, compared to none oscillation and sinusoidal oscillation, the lower cooling rate under circular oscillating pattern contributes to the formation of equiaxed grains. The fine equiaxed grains are easy to move and form an ordered lattice structure, which favors the transformation of low-angle grain boundaries and the increase in the strength of the crystal texture. Therefore, with oscillation frequency and amplitude set at 80 Hz and 0.8 mm, respectively, the use of circular oscillating pattern in laser welding results in an improvement in weld seam microstructure.

Microstructure evolution and fracture behavior of 2060 Al[sbnd]Li alloy by laser welding with TiC nanoparticle-reinforced filling wire

Laser welding could provide thermal concentration and penetration to alloys, making microstructural diversity that determines mechanical properties. During laser welding process of aluminum alloys, one of the most important characteristics is the inhomogeneity of microstructure. The study demonstrated microstructure transformation of 2060 aluminum-lithium (AlLi) alloy in laser welding technique using TiC nanoparticle-reinforced filling wire to tailor mechanical properties. Furthermore, the study unveils the microstructural configuration achieved during laser welding of the 2060 AlLi alloy, along with its fine-scale mechanical behavior. The results show that the microstructure of weld seam (WS) with TiC nanoparticle-reinforced ER2319 filling wire was dominated by fine equiaxed crystal, which indicated that the addition of nanoparticles promoted the transformation from columnar crystal to equiaxed crystal. Compared with conventional ER2319 filler wire, the grain size with adding TiC nanoparticles reduced by 47 %, and the strong texture feature of Al-matrix on (001) base plane tended to disappear. Furthermore, the tensile strength and elongation of WS were increased by 8.6 % and 195.5 %, respectively. The direction of crack propagation is deflected under filler ER2319CT wire, gradually tends to be perpendicular to the load direction. This is attributed to the fact that the dispersed TiC particles in WS hinder the movement and migration of dislocations resulting in an increase of strength.

The effect of shielding gas on weldability of the AISI 420 martensitic stainless steel

Abstract Most of weld defects occurring in the welding of martensitic stainless steels are caused by the presence of hydrogen. Thus, the effects of hydrogen in the weld zone need to be well-understood to estimate the quality and service life of martensitic stainless steel joints. In the present study, AISI 420 martensitic stainless steel materials were welded by using different combinations of shielding gas via the gas metal arc welding (GMAW) method. It is known that shielding gases also play a critical role in heat input, cooling rate, microstructure of weld seam, weld defects, and mechanical properties besides drying of molten weld pool. Thus, it is important to investigate the effects of shielding gases and gas combinations on the welding of martensitic stainless steels in the welding process. In the present study, 100 % Ar, 97 % Ar + 3 % H2 and 93 % Ar + 7 % H2 gas combinations were employed. The welded sheets were subjected to the metallographic examination as well as hardness, tensile, and bending tests. The effect of the tests and the combination of shielding gas on the mechanical and microstructural properties of AISI 420 stainless steel was investigated. The results indicated that a noticeable grain coarsening occurred in the microstructure of the weld metal and heat affected zones (HAZs) after the addition of H2 into the Ar gas during the welding process. The highest tensile strength was obtained from the joints with 100 % Ar gas. As a result of the tensile test, rupture occurred in the base metal-HAZ transition zone in all the welded samples. In the joints welded with 97 % Ar + 3 % H2 and 93 % Ar + 7 % H2 gas combinations, fracture occurred in the base metal-HAZ transition zone during the bending test.

Effect of weld microstructure on the tensile properties and impact toughness of the naval, marine-grade steel weld joints

Pulsed direct current (PDC) gas tungsten arc welding (GTAW) of 12 mm thick plates of naval, marine-grade high strength low alloy steel (HSLA) using ER80S–Ni3 filler metal was investigated. The microstructural characteristics were examined by both optical microscopy and field-emission scanning electron microscopy (FE-SEM) techniques. The fusion zone is comprised of mixed microstructures of acicular ferrite (AF), polygonal ferrite (PF), grain boundary ferrite (GBF), and bainite ferrite (BF) laths in the various welding passes. The yield and tensile strengths of the PDCGTA weld joints were found to be superior to that of the base metal. A joint efficiency of 122% was observed for the weld seams while conducting the notch tensile studies (NTS). The impact toughness of the weld joints was higher than that of the base metal. The tensile and impact properties in the room temperature (RT) conditions were superior due to the formation of acicular ferrite (AF) and bainite ferrite (BF) laths in the weld seam microstructure. A higher toughness value of 173 J and ductile fracture mode was observed when the joints were impact loaded at −40 °C. On the other hand, the brittle cleavage fracture was observed for the joints subjected to impact loading at −196 °C. The impact toughness data indicated that the joints experienced a transition from a ductile to a brittle mode of fracture on lowering the temperature.

Experimental Investigation of Temperature and Contact Pressure Influence on HFI Welded Joint Properties.

This paper presents an experimental electro-thermo-mechanical simulation of high-frequency induction (HFI) welding to investigate the effect of temperature and contact normal stress on the weld seam quality. Therefore welding experiments at different temperatures and contact pressures are performed using flat specimens of 34MnB5 steel sheet. In order to characterize the weld seam strength of the welded specimens, tensile and bending tests are performed. To obtain a relative weld seam strength, the bending specimens were additionally hardened prior to testing. With the hardened specimens, it can be shown that the weld seam strength increases with increasing temperature and contact normal stress until a kind of plateau is formed where the weld seam strength remains almost constant. In addition to mechanical testing, the influence of the investigated process parameters on the weld seam microstructure is studied metallographically using light optical microscopy, scanning electron microscopy, EBSD and hardness measurements. It is shown that the weld seam strength is related to the amount of oxides in the bonding line.

Application of Electrochemical Noise to Investigate Role of Microstructural Evolution on Inhibiting Stress Corrosion Cracking of Ti–6Al–4V Weldment

Using the electrochemical noise method, this paper studies the effect of microstructure of weld seam on the stress corrosion cracking behavior of Ti–6Al–4V alloy weldment. Local rapid induction heating can significantly change the microstructure, and the acicular α′ martensite phase in the weld seam is decomposed into lathy α phase and transformed β phase. The higher heat temperature leads to more transformed β phase and less lathy α phase. The mechanical properties and stress corrosion cracking sensitivity during the slow strain rate tensile test are significantly affected by the microstructure of weld seam, which are improved with the decomposition of acicular α′ martensite and decrease of lathy α phase content combined with increase of transformed β phase content. Compared with the non-treated sample, the induction heating enhances the corrosion resistance of the sample and delays the occurrence time of localized corrosion during the slow strain rate tensile test. The higher corrosion resistance and the later occurrence time of localized corrosion are caused by the higher induction heating temperature. The microstructural evolution of the weldment significantly inhibits the stress corrosion cracking process.

The effect of cryogenic applications on tensile strength of aluminum 2219-T87 T-joint welded by dual laser-beam bilateral synchronous welding

2219 aluminum alloy has been widely used in aerospace industry due to its high specific strength, excellent weldability as well as outstanding ductility. The dual laser-beam bilateral synchronous welding (DLBSW) technology is employed in the joining of 2219-T87 aluminum alloy skin-stringer structure in T-joint. In order to establish the tensile strength of T-joints at room and cryogenic temperatures, the tensile testing is carried out. The microstructure of weld seam is observed for exploring the relationship between the grain size and tensile strength. In addition, the fracture morphology is observed by scanning electron microscope (SEM). The elemental analysis of fractured surface is done by energy dispersive spectrometer (EDS) and is used to study the effect of chemical element composition on tensile strength. The results show that the highest tensile strength of 360.01 MPa was achieved when the tensile test obtained at room temperature while the joint welded by same parameter exhibit a much higher tensile strength of 422 MPa when tested at cryogenic temperature. According to the results of microstructure analysis, grain size reduction was observed when the joint was exposed to cryogenic temperature. From the fracture morphology of joints, it was found that dimples of the sample tested at cryogenic temperature are bigger and deeper than that at room temperature. The results of EDS show that the amount of the Al2Cu increases at 77 K which causes an increase in tensile strength.

Direct ageing response on the microstructure and mechanical properties of electron beam welds of Ni-Cr-Fe alloy used in vacuum insulated tubing

Incoloy 925 joints of 5 mm thick were accomplished by adopting high energy density, electron beam welding (EBW) process. Although the weld seam microstructure was completely austenitic and free from solidification cracking, the heat-affected zone (HAZ) of EBW joints experienced liquation cracking. The mechanical behaviour of the EB weld seams in the as-welded and direct aged (DA) at 732 °C for 4 h and air-cooled conditions were compared. Electron backscattered X-ray diffraction (EBSD) analysis revealed the formation of strengthening precipitate γ′ in the matrix and the precipitation of sigma (σ) phase, M7C3, M23C6 and Ti-rich carbides formed along the crystallite boundaries in the DA condition. The tensile property outcomes opined that the joint efficiency of the weld seams in the DA condition (99.32 %) was found to be better than the ones in the as-welded condition (71.32 %). Also, the yield strength has been considerably improved in the EB weld seams subjected to DA conditions. The carbide precipitation along the grain boundaries is discontinuous and also not effective in pinning the dislocations under impact loads.

Optimization of transversal flow stress and strain and weld seam microstructure analysis in butt-HDPE friction stir welded plates

The paper aims to optimize the characteristic performances of friction stir welding of high-density polyethylene in order to predict failure modes in weld nugget and interfacial zones. Three replicates of a face central composite design are employed to estimate the effects of parameters process, on the transversal flow stress and strain of the seam and to understand root causes, which may lead to structural defects such as the onset of cracks and the seam-base metal rupture. The study findings disclose that maximum responses are obtained when the tool rotation speed is set middle and both the feed rate and the plunged surface are set high. The transversal flow stress of the welded seam is found highly sensitive to the plunged surfaces and at a lesser degree to the rotation speed, whereas, the transversal flow strain of the welded seam is mostly sensitive to the rotation speed and at a lesser degree to the plunged surfaces. For the microscopic analysis, it is shown that at low rotation speed, there exist four structural layers in the transition zone between the seam and the base material giving rise to the formation of a continuous line of cracks that can initiate structure failure.

Microstructure and mechanical integrity relationship of PDC weld joints involving dissimilar marine grade alloys

The fillers ER80S-Ni3 and ER2553 were deployed to obtain 10 mm thick joints of super-duplex stainless steel (SDSS) and high strength low alloy (HSLA) steel using pulsed direct current (PDC) welding approach. Laths of martensite/bainite with retained austenite were observed in the weld seam microstructure of ER80S-Ni3 joints; whereas austeno-ferrite microstructure was seen in ER2553 joints. Considerable changes in the ferrite percentage was noticed in the fusion region of ER2553 joints. Repeated thermal cycles resulted in austenite reformation and thus a lower ferrite percentage was ascertained in the root pass of ER2553 joints. The tensile ruptures were occurred on the base metal region of HSLA for both the cases. Notch tensile studies demonstrated that the weld seams employing ER80SNi-3 filler imparted better strength and failure occurred in the base metal of HSLA. A decrease of 19 % and 76 % in the impact toughness was observed for ER2553 and ER80S-Ni3 joints when operated in room temperature (RT). The impact toughness of the weld seams was drastically deteriorated while operating at −196 °C, reasoned to the ductile to brittle transition.

Effect of solid state phase transformation on the residual stress in multi-pass weld plates of S355J2W steel

The coupling model of temperature-phase transformation-mechanics is constructed in this paper. The effect of solid state phase transformation and different hardening models on the residual stress distribution of S355J2W welded joints have been studied with finite element method (FEM) simulation. The microstructure, micro hardness and residual stress of welded joints are also studied. It has been shown that the microstructure of weld seam is composed of bainite structure with little martensite, while the base metal is ferrites and pearlites. The simulation results by FEM were in good accordance with the X-ray results. The maximum tensile residual stress is 463 MPa in the weld. The tensile residual stress was decreased with the larger distance to the weld.

Effect of Microstructure of Welded Joints HG785D on Impact Toughness

The microstructure and impact toughness of joints of HG785D high strength steel welded by metal active gas shielded arc welding (80%Ar+20%CO2) was observed and analyzed. The result showed that the microstructure of weld seam was mainly composed of acicular ferrite, the impact energy of which was better. While the microstructure of HAZ with large size bainite and M-A island. Using the method of EBSD, it's also found that the effective grain size of weld seam was similar with fine grain HAZ. However the proportion of high-angle grain boundary in weld seam was much larger than that of HAZ. As a result, it could arrest propagating cracks and enhance the toughness.

Microstructure of Welding Seam and its Effect on Propagation of Microcracks in Nulear Gade Z3CN20-09M Sainless Seel

The microstructure of welding seam was characterized by optical microscope and SEM,and then of which the effect on crack propagation was studied by means of situ tensile test in SEM and EBSD technique for a nuclear grade stainless Z3CN20-09 M.The results show that the weld seam composes of lath- shaped and island- like microstructures and different microstructures exhibited different resistance to crack propagation.Island-like microstructure has a strong resistance to the crack propagation,which can induce a deflection of the path way of crack propagation; while lath-shaped structure showed little effect on crack propagation,and the crack passed though the lath- shaped microstructure quickly without any deflection.

Study on Formability of Tailor Welded Blanks Based on Numerical Simulation

The strength ratio, thickness ration of blanks and the microstructure of weld seam play important role in the formability of tailor welded blanks (TWB). With numeric simulation technology in different conditions such as different thickness and different strength combination of TWB’s materials, the forming limit depth (FLD) of tailor welded blanks is analyzed. The affect of the thickness ratio and strength ratio on forming limit depth is investigated, the laws influencing the formability of TWB square box are summarized, and approaches are presented to increase the FLD. The results of simulation and practice indicate that reducing the difference of the thickness ratio, choosing lower strength material for thicker blank, and adopting right heat treatment can improve the forming limit depth. Keywords: Tailor Welded Blanks; Forming Limit Depth; Thickness Ratio; Strength Ratio

Experimental study of electron beam welding of magnesium alloys

The joints of AZ31 magnesium alloys welded by the electron beam welding with different parameters were studied. The relationship between the processing parameters and the microstructure and mechanical properties was investigated. The microstructure, mechanical properties and fracture pattern of the welding joints were investigated by the metallographic microscope, the universal tensile testing machine and the scanning electronic microscope (SEM). The results show that the penetration has a certain ratio relationship with the electron beam current while it is insensitive to the welding speed. The weld shape is good when appropriate parameters are applied. The weld seam microstructure consists of fine equal-axed grains. The tensile strength of the welding joints is about 55 % of the base metal. The joints fracture pattern is a mixed one of the brittle fracture and ductile fracture.