Properties Of Welds Research Articles

Microstructure and properties of laser welding Ni-based alloy/austenitic stainless steel with filler wire for nuclear reactor pump can end sealing

The current study investigates the microstructure and properties of laser welding involving Hastelloy C-276 and 304 stainless steel with filler wire, which is closely related to nuclear reactor pump can end sealing. The experimental results indicate the presence of an unmixed zone (UZ) and a small amount of Mo-rich secondary phase in weld seam, and microstructure of UZ is composed of austenite and ferrite phases. Laser welding enhances the ratio of low-angle misorientation and the uniformity of elements macro-distribution. The end sealing property of nuclear reactor pump can is characterized by anti-peel property of weld joints. The welded joint has local fracture and through fracture in the test of anti-peel property. The weld with local fracture exhibits superior anti-peel property. The joint crack starts at the bottom of the UZ. The anti-peel property of the welded joint is 239.6 ± 4.7 N/mm and mainly related to the weld penetration. The corrosion property of welded joints is determined by the elements of the weld, and the welded joints showcasing a better integral corrosion property than that of 304 base metals. Laser welding Ni-based alloy/austenitic stainless steel with filler wire has significant technical advantages for end sealing of nuclear reactor pump can.

Improving bonding strength of medium-thick Al-Cu dissimilar joint by a novel splat cooling assisted double side friction stir welding

To obtain a high-strength medium-thick Al-Cu dissimilar joint, a novel splat cooling assisted double side friction stir welding (SDS-FSW) is proposed. The microstructure and tensile properties of conventional double-side friction stir welding (DS-FSW) and the novel SDS-FSW joints under optimal welding parameters are systematically compared, it shows that the utilization of in-process splat cooling significantly reduces the welding peak temperature and the high-temperature dwell time. The in-process splat cooling causes significant grain refinement in the welding nugget zone (WNZ) of the Al-Cu dissimilar SDS-FSWed joint, it exists the lower recrystallization fraction and the higher KAM value. Although both DS-FSW and SDS-FSW joints fracture at the Al-Cu interface, the DS-FSW joint represents a brittle fracture characteristic, while the SDS-FSW joint represents a mixed ductile-brittle fracture mode. Under the drive of the mechanical stirring of the tool and the welding thermal cycle, the aluminium atoms and copper atoms diffuse to the copper base material and aluminium base material, respectively. Since copper diffuses in aluminium at a higher diffusion rate than aluminium diffuses in copper, and the solubility of copper in aluminium is much smaller than that of aluminium in copper, thus the Al2Cu becomes the first phase with the nucleation and growth. As the welding temperature and time continue to increase, Al2Cu reaches the supersaturation state, and the Al4Cu9 phase is produced between the Cu (Al) and the Al2Cu phase. In the end, the interface forms the stable double-layer IMCs structure (Al2Cu/Al4Cu9). The optimal tensile strength of the SDS-FSWed joint is 159 MPa, which is increased by 42% compared to the DS-FSWed joint at the same welding parameter. This was mainly because in-process splat cooling contributed to forming a thinner IMCs layer at the A-Al-Cu interface. It reveals that the application of in-process splat cooling is a versatile method to thin the IMCs layer at the Al-Cu medium-thick DS-FSW process.

Effect of welding speed on mechanical properties of dissimilar friction stir lap-joint welding between AA6061 and C1100 copper

Nowadays, renewable energy such as wind and solar energy can be employed for marine application to enhance clean and green technology. So, using battery is necessary to apply power for ship activities. To contribute sustainable development, optimizing structure in electric transmission such as bimetal connector Cu-Al is necessary to improve joint quality. This study focused the influence of welding parameters on the quality of the lap-joint between AA6061 aluminum alloy and C1100 copper. Experimental results indicate that the welding interface was sensitive to welding speed. Some welding defect was found in the joint such as tunnel and hook defects. The highest tensile strength produced by the welding speed of 200 mm/min was approximately 1100 N. In all experimental regimes, the weld zone structure, hardness distribution, tensile strength, fracture location, and local deformation were analyzed and discussed in detail. Keywords: Friction stir welding, microstructure, mechanical properties, hardness

Investigation of The Weldability of PLA Plus Sheets with Different Infill Ratios by Friction Stir Welding

Although the joining processes of plastics are typically carried out through welding, adhesive bonding, or mechanical fastening elements, the production of complex and large parts often requires welding technology. In this study, the effect of part infill ratio (20%, 40%, 60%, 80%, and 100%) on the welding strength of 3D printed PLA Plus parts was evaluated through friction stir welding (FSW). Tensile tests and temperature measurements were carried out to examine the effects of friction stir welding process parameters (feed rate: 50 and 100 mm/min and rotational speed: 1000 and 1500 rpm) on the structure and mechanical properties of friction stir welding. Moreover, visual inspections were performed to detect defects in the weld zone. Compared to the PLA Plus samples given as reference according to the infill ratios, the highest welding strengths were obtained at 80%, 60% and 100% infill ratios (29.4 MPa, 17.47 MPa and 41.12 MPa and 112.38%, 97.48%, 87.04% efficiency, respectively). As a result, it was determined that at low infill ratios (20% and 40%), the weld quality was negatively affected, and a surface tunnel defect occurred in the weld zone. It has been determined that the weld quality in FSW is significantly affected by the temperature occurring during the process. The study has shown that parts printed at different infill ratios, especially on a 3D printer, can be combined with friction stir welding and that the efficiency of the welding process can be increased by optimizing the infill ratios.

Investigation on the formation mechanism of collapse defects, microstructural evolution and mechanical properties in full penetration laser welding of thick-section steel

In this paper, we described full penetration laser welding (FPLW), a process capable of achieving single-pass welding of thick-section steel. This work summarized a welding process window encompassing various typical formations, including those well-formed and collapse defects. Furthermore, collapse defects were categorized as “collapse formation with backside humping” and “collapse formation with underfill”. High-speed camera (HSC) images reveal that the formation mechanisms of these two defects are attributed to the accumulation of liquid metal at the rear edge of the bottom molten pool and the ejection of a large amount of liquid metal from the weld in a spatter form, respectively. A computational fluid dynamics (CFD) numerical simulation model well-aligned with the experimental results has been established. The analysis of the molten pool flow behavior and keyhole evolution revealed that during well-formed welding, the keyhole status in the welding process exhibits a periodic closure-collapse mode. This periodic mode can instantaneously release the pressure at the bottom of the keyhole, inhibiting the excessive accumulation of liquid metal at the bottom of the weld and thus inhibiting the formation of collapse defects. The cooling rate in the upper part of the weld exceeds that in the middle and lower parts, primarily resulting in the formation of fine acicular ferrite and martensite. The increased tensile strength exhibited by the welded joint relative to the base material predominantly emanates from the mechanisms of grain boundary reinforcement and dislocation strengthening, precisely caused by the refined microstructure.

Ultrasonic complex vibration source equipped with a step horn with a welding tip and its welding characteristics

We have developed a different type of ultrasonic complex vibration source that can generate planar vibrations. The ultrasonic complex vibration source is equipped with a step horn with a hollow part that incorporates a welding chip to improve practicality for industrial applications. The hollow portion in the step horn attached to the ultrasonic complex vibration source enables the adjustment of the longitudinal and torsional vibration amplitude. In this work, we performed finite element method analysis to develop the ultrasonic complex vibration source equipped with a step horn containing a hollow part and a welding tip. The ultrasonic complex vibration source was manufactured and the vibration characteristics and welding properties were measured. The same welding strength was obtained under similar experimental conditions to conventional ultrasonic complex vibration sources. Our results demonstrate that ultrasonic complex vibration sources can be miniaturized and are practically useful.

Effects of beam oscillation on porosity and microstructure of laser welded TC11 titanium alloy

Oscillating beam was used for laser welding of TC11 titanium alloys. The porosity, microstructure, and mechanical properties of welds with different parameters were studied. It was found that increasing the oscillation frequency could effectively suppress porosity. When the oscillation amplitude was less than or equal to 1 mm, the laser power was about 3 kW, and the welding speed was less than 15 mm/s, porosity could be effectively suppressed. Both oscillation frequency and amplitude could increase the number of α′-phase. The oscillation frequency promoted the cross distribution of α′-phase and α″-phase in the columnar crystal. The oscillation amplitude promotes the uniform distribution of α′-phase in the columnar crystal. Increasing the oscillation frequency and the oscillation amplitude was beneficial to increase the tensile strength. In the case of low defect rates, the tensile strength of the weld could reach more than 90% of the base metal, and the maximum elongation was 7.5%.

Microstructure and Mechanical Properties of Powder Metallurgy Superalloy Joints Welded by Inertia Friction Welding.

In recent years, for the structural characteristics and design requirements of the integral rotor and disc shaft of the integrated engine, the welding quality and mechanical properties of superalloy weldments have received increasing attention. In this paper, inertia friction welding (IFW) of FGH96 alloy was carried out using different welding parameters, and the homogeneous connection of FGH96 alloy hollow bars was successfully realized. The microstructure evolution, mechanical properties and fracture failure of the welded joints at room and high temperatures were investigated. The FGH96 alloy IFW joints were divided into the weld nugget zone (WNZ), the thermo-mechanically affected zone (TMAZ), the heat-affected zone (HAZ) and the base metal (BM), and there were significant differences in grain structure and distribution of the γ' phase in each of the characteristic zones. The microhardness and tensile properties of the IFW joints were investigated, and the results showed an "M"-shaped curve in the microhardness distribution, with the lowest point of hardness observed in the HAZ. The tensile test results indicated that the fracture position moved from the BM to the WNZ with the increase in temperature, the microstructure at the fracture changed significantly and the tensile strength decreased from 1512.0 MPa at room temperature to 1201.3 MPa at 750 °C. The difference in the mechanical properties of the joints was mainly attributed to the changes in the dissolution and precipitation of the γ' phase.

Rotary friction welding properties of AA5083-H112/AA7075-T6 joints: Parameter and low temperature effect

This study presents experimental findings from rotary friction welding of AA5083-H112 and AA7075-T6, conducted at consistent 1700 rpm rotational speed with four time intervals. The focus was on exploring the welding parameters influence on joint properties, assessed through mechanical testing, metallography and hardness tests. Prolonged welding led to elevated temperatures, expanding the heat-affected zone, grain growth and microhardness at the interface. The temperatures effect on joint toughness was evaluated through Charpy impact testing at different temperatures, showing lower impact strength at −192 °C. Fracture surfaces exhibited increased micro voids and dimples as the temperatures decreased. The study highlighted a positive link between extended welding times and improved cryogenic impact strength and mechanical properties.

Effect of Welding Process Parameters on the Mechanical Properties of TIG and MIG Welds in HSS X65 Pipe-A Review

The study focused on the importance of the different welding parameters on the mechanical behavior of High Strength Steel (HSS) X65 steel pipes by reviewing the advantages of parameter optimization for the Tungsten Inert Gas (TIG) - Metal Inert Gas (MIG) welding processes. The parameters considered in the study include welding speed, welding current, welding voltage and gas flowrate of the welding. The effects of improper selection and parameter optimizations were highlighted and illustrated using different metallurgical and mechanical instances. The outcome of the study indicates that adequate parameter optimization aids in obtaining good weld quality with adequate mechanical and microstructural properties. Furthermore, it helps in the determination of variation in hardness in the heat affected zone as well as the base metal. Thus, this study provides insight to welding engineers on the importance of parameter optimization in the welding of steel pipe.

Influence of reduced pressure on arc and weld pool properties in TIG welding

In this article, transient transport phenomena in the arc and weld pool for different ambient pressures during tungsten inert gas welding were reported. Arc plasma and weld pool behaviour vary with ambient pressure because of changes in arc thermophysical properties. The maximum arc temperature decreases with decreasing ambient pressure because of reduced plasma electrical conductivity. Decreased arc mass density results in a lower maximum weld pool surface temperature and a decrease in maximum metal vapour content as ambient pressure decreases. Arc pressure decreases with decrease in ambient pressure, resulting in shallower penetration. Calculated arc temperature distribution and weld cross-section are compared with experiments to validate the modeling method for simulating heat and mass transfer phenomena in low ambient pressure welding.

Microstructure evolution and enhanced cryogenic toughness of laser welded dissimilar SA645/AISI304L joints via intercritical tempering

In this study, we explored the impact of intercritical tempering on the microstructural evolution and mechanical properties of dissimilar welds formed through laser welding between 5%Ni steel (SA645) and austenitic stainless steel (AISI304L). Upon tempering at 500 °C, reversed austenite manifested within the weld metal. The volume proportion of reversed austenite in weld metal at room temperature increased first, exhibiting a maximum (∼10%) at ∼600 °C, and then decreased with increasing tempering temperature, which was associated with the diminished stability of austenite. Due to the change in tempering temperatures, two distinct types of reversed austenite were present, with one being located at the high-angle grain boundaries and the other within the martensite blocks. As the tempering temperature increased, the weld metal hardness decreased, reaching a minimum of ∼306 HV at 600 °C, and then increased. The dislocation density within the martensite matrix and the quantity of reversed austenite are the crucial factors to determine the hardness of weld metal. The cryogenic impact toughness of weld metal increased at first and then decreased as the tempering temperature increased. The maximum of ∼40 J for the cryogenic impact toughness was obtained when tempering at 600 °C. The low-temperature impact toughness of the weld metal was determined by the synergy of the TRIP effect of reversed austenite, the compatible deformation capability of dual-phase structure, and the crack propagation behavior.

The strengthening role of post-welded cryogenic treatment on the performance and microstructure of 304 austenitic stainless steel weldments

The metallurgical changes and micro defects after welding can influence the mechanical property, corrosion resistance and dimensional stability of the stainless steel wielding joints. It is necessary to explore an effective post-welded method to improve the service performance for stainless steel welding joints. Furthermore, the essential mechanism between microstructure changes and macro-property variation during this process needs deep reveal. Therefore, this paper aims at investigating the effects of different post-weld treatments including naturally aging, artificial aging and cryogenic treatment on the residual stress and mechanical properties of 304 stainless steel weldments. The microstructure evolution was also studied to reveal and establish the microstructure-performance relationship. The results showed that the distribution of residual stress was most uniform with lowest magnitude (decreased by up to 49%) after cryogenic treatment. At room temperature, weldments subjected to the three post treatments showed similar mechanical properties. At cryogenic temperature, cryogenic treatment exhibited an outstanding role on maintaining the mechanical properties of weldments. By contrast, the mechanical properties were obviously reduced by artificial aging. The transformation of δ-ferrite and the carbide precipitation in grain boundaries are the main reasons for the decrease of mechanical properties after artificially aging. Welding process was able to cause the transfer of the alloying elements and decrease the stability of austenite. Consequently, martensitic transformation can be induced during cryogenic treatment. The new formed martensite resulted in the refined microstructure and high mechanical properties of weldments, and also the release of residual stress after welding.

Characterization of Mechanical Properties of Welds of Q355D Steel by DSI Technique

Characterization of Mechanical Properties of Welds of Q355D Steel by DSI Technique

The effect of heat input on tensile strength, Vickers hardness, and microstructure on DMW of AISI 1015 and 304L SS through the GMAW process

This experiment was to evaluate the effect of heat input on tensile strength, Vickers hardness, and microstructural observations.The materials welded are AISI 1015 and 304L SS, and the joining process is Gas Metal Arc Welding (GMAW). The filler electrode used is ER70S-6 with a diameter of 1.2 mm, and the workpiece size is 300 x 125 x 3 mm with a butt-joint connection. The variations in welding current applied are 120, 130, and 140 A. Meanwhile, the voltage and welding speed in the experiment were kept constant.The maximum tensile test index was 380.08 MPa, and the Vickers hardness index was 376.85 HV, with the maximum heat input being 0.5943 kJ/mm. The macro- and microstructure, as well as structural inspection of the welded joints, were observed in the experiment. The best heat input effect for the DMW technique between 304L SS and AISI 1015 is 0.5943 kJ/mm at a plate thickness of 3 mm.Dissimilar Metal Welding (DMW) is widely applied in the power generation industry. Materials generally joined using the DMW technique are austenitic stainless steel (304L SS) and low carbon steel (AISI 1015).Using the proposed heat input approach is important for the dissimilar welding industry application to obtain the right product for its expected use.This paper presents the differences in heat input to reveal the weld properties by dissimilar welding processes, where the properties will be adapted for a particular use. Particularly in the application of dissimilar joints between 304L SS and AISI 1015 with a thickness of 3 mm, which requires an average tensile strength of around 380.08 MPa and an average yield strength of about 320.16 MPa, the heat input parameter can be recommended as 0.5943 kJ/mm.

Polypropylene for material extrusion: Evidence that flow-enhanced crystallization restricts welding

We present a comprehensive investigation into the effect that both the crystallization kinetics and the molecular weight of polypropylene feedstock have on the welding properties in material extrusion 3D-printing (MatEx). As sufficient welding at the interfaces between printed layers may be restricted by the onset of crystallization, there is a delicate balance between polymer interdiffusion and the development of spherulites within the weld region. We monitor these processes during a cooling cycle using a well-established theoretical model that requires full characterisation of the rheology and crystallization. The model shows that the largest effect of increasing molecular weight is a reduction in interdiffusion; this mechanism leads to a reduction in the weld strength as demonstrated by mechanical testing. For the highest molecular weight feedstock, we find that the fracture pattern changes from plastic deformation to brittle mode. Furthermore, we observe that the spherulites within the weld are about an order of magnitude smaller than in other samples. These observations cannot be described by the quiescent crystallization kinetics alone. Our findings suggest that it is a flow-enhanced crystallization mechanism that accelerates nucleation leading to smaller spherulites developing in the weld earlier in the cooling process. This significantly restricts interdiffusion at the welds.

Local mechanical properties of dissimilar metal TIG welded joints of CoCrFeMnNi high entropy alloy and AISI 304 austenitic steel

Multiple principal element alloys encompass the well-known high entropy alloys (HEA). The alloy system represents a new class of materials consisting of at least three alloying elements, each containing 5 to 35 at.%. Thus, this alloying concept differs fundamentally from conventional materials such as steel or nickel alloys. For this purpose, the alloying elements are specifically selected, the microstructures are adjusted in a single-phase and, in some cases, multi-phase manner. In particular, conflicting goals, such as the trade-off between strength and ductility in conventional steels, are overcome. However, in the last 20 years, the focus has been on material synthesis. With the increase in available material quantities, the focus is now on processing issues such as joining and welding processes. The weldability of HEAs has received very little attention so far. The experience with dissimilar metal welds is completely lacking but is essential for the application of these materials in combination with conventional materials. The present study presents comprehensive experimental results on the weldability of an equimolar CoCrFeMnNi-HEA in cold-rolled and heat-treated condition, which was joined by tungsten inert gas welding to an austenitic steel AISI 304. The mechanical properties of the dissimilar metal welds were characterized by cross-weld tensile samples, whereas the local deformation in the weld of the different welding zones was measured by digital image correlation. In accordance with the respective initial HEA condition (cold-rolled vs. heat-treated), the local strain behavior was divergent and influenced the global mechanical properties of both DMW types. Nonetheless, the experiments provided proof in principle of the weldability for dissimilar joints of the CoCrFeMnNi-HEA welded to conventional materials like austenitic stainless steels ensuring a corresponding capability for mechanical loading. This allows further considerations on the application of these innovative materials.

Alloying systems for modern flux-cored wires for mechanized welding in shielding gases of high-strength shipbuilding steels

An analysis of the domestic market for flux-cored wire used for welding low-alloy high-strength shipbuilding steels has been carried out. It has been established that to ensure a guaranteed value of the yield strength of the weld metal from 420 to 620 MPa, alloying systems such as Mn–Si, Mn–Si–Ni and Mn–Si–Ni–Mo are taken as a basis. The influence of alloying elements used in these systems on the formation of the microstructure and properties of welds was experimentally established.

Effect of ingredients proportions on mechanical properties in laser-coated WC-blend welds

Abstract In this study, we investigated ceramic-matrix composite coatings created by laser cladding on 45 steel using tungsten carbide (WC) powder with varying weight percentages of Co or Ni additives. Our analysis focused on the influence of Co additives in WC powders on the key properties of the coatings, including the microstructural evolution, hardness, wear, and residual stress behaviors. High residual stresses led to significant cracking in coatings comprising 100% WC. The addition of Co at a concentration of 20% to WC reduces the cracking activity. The microhardness of the coating exceeded that of the substrate by a factor of more than five. The microstructural evolution revealed a typical intergranular fracture in the molten zone, with cracks propagating through the interior of the unmelted WC at 100% WC. In addition, by adding Ni alloys, the composite coatings were extended to three mixtures: WC-Co, WC-Ni, and WC-Co-Ni. The relationship between the three-component mixtures and wear volume of the laser cladding was established, and the ratios of the three-component mixtures were optimized. A reduced quadratic model for three-component mixtures, which provided a better mixture ratio pattern, showed an excellent fit. Based on the experimental results, the developed three-component mixture with better mixture ratios can enhance anti-wear behavior. A satisfactory agreement was obtained between the predicted and experimental values of the wear volume of the laser-coated welds. Overall, our study accomplishes the optimization of the mixture ratio of the three components, which ensured a reduction in the wear of the welds, thereby improving the performance of laser-coated welds.

Measurement of Mechanical Properties of Friction Stir Welding of Al–Li alloy under different environmental conditions

Measurement of Mechanical Properties of Friction Stir Welding of Al–Li alloy under different environmental conditions