Microhardness Of Weld Metal Research Articles

Effect of heat treatments on microstructure and mechanical behavior of laser welded LPBF AlSi10Mg alloys

In this work, heat treatments were performed on autogenously laser welding of laser powder bed fusion (LPBF) AlSi10Mg alloys to improve mechanical properties of welded joints. After welding, the welded joint was heat treated by direct aging (DA) and solution heat treatment and artificial aging (T6) treatment. The porosity, microstructure and mechanical performance of the welded joints after DA and T6 treatments were investigated and compared with the as-welded joint. Results show that the microhardness of weld metal (WM) has been increased to over 93.5 HV0.1 after DA treatment, while the microhardness in the T6 welded joint is reduced to 77.0 HV0.1, from 82.0 HV0.1 in the as-welded joint. The ultimate tensile strength (UTS) of the DA treated joint reaches 276.5 MPa, showing an increase of 43.0% compared with as-welded joint. The DA heat treatment of the LPBF AlSi10Mg welded joints effectively improves the hardness and the UTS, which can be mainly attributable to the reduction of the hydrogen pores, the enhancing effect of solid solution strengthening coming from the Si element in the Al matrix and the dispersion strengthening of Si precipitation.

Effect of SAW electrode wire preheating current on its melting rate and weldment properties of HSLA steel joint

ABSTRACT Weld strength and quality are mostly affected by process parameters, which, in turn, influence the mechanical properties of weld metal and heat affected zone. In this research work, effect of electrode wire preheating on different responses including electrode wire melting rate, wire and plate melting efficiency, width of heat affected zone, microhardness, and corrosion rate of weld metal was studied. The experiments were carried out to accumulate the response data using the optimisation techniques. Then, the quadratic mathematical models were developed and checked the significance using the tests such as ANOVA, F-test and lack of fit. The preheat current is found to be the most contributing parameter, which efficiently enhanced the wire melting rate, wire melting efficiency and microhardness of weld metal whereas reduced the plate melting efficiency, heat affected zone (HAZ) width and corrosion rate. In addition, micrographs and micro-hardness results also confirmed the significant influence of preheat current.

Comparative study of SAW and ASAW process on ASTM A709 Grade 36 steel welds

Welding is a versatile fabrication process used in manufacturing industries for joining structural components. The welded structure's capacity to carrying loads is affected by bead characteristics and process parameters. In this research work, the influnce of the Submerged Arc Welding and Advanced Submerged Arc Welding process on heat input, area of penetration, reinforcement, and heat affected zone, electrode melting rate, electrode and plate melting efficiencies, flux consumption, metal deposition rate, the microhardness of weld metal and HAZ, the microstructure of weld metal zone and power consumption have been studied. The experiments were carried out with the bead on plate (BOP) technique in ASTM A709 Grade 36 steel. The Advanced Submerged Arc Welding process reduces the heat input and area of heat affected zone. At the same time, it increases the area of reinforcement height, electrode melting rate, electrode melting efficiency, metal deposition rate and flux consumption. The microhardness of both zones of the Advanced Submerged Arc Welding process is higher than the Submerged Arc Welding process. Moreover, the microhardness of the heat affected zone is higher than the weld metal zone. The microstructures show the ferritic structure with columnar grains, whereas the column size reduces in the Advanced Submerged Arc Welding process. The Advanced Submerged Arc Welding process reduces the power consumption by 20.59% compared to the Submerged Arc Welding process.

Follow-up ultrasonic vibration assisted laser welding dissimilar metals for nuclear reactor pump can end sealing

A novel follow-up ultrasonic vibration assisted welding process was proposed to reduce the common defects in laser welding of dissimilar metals for nuclear reactor pump can end sealing, such as unmixed zone, precipitated phase, and uneven element distribution. The influences of ultrasonic vibration on morphology, microstructure and property of C-276/304 laser-welded joint was analyzed. The results indicated that, the most significant ultrasonic vibration at welding position was achieved at parameters of 25 N pressing force and 13 mm distance from ultrasonic action point to welding position. By the application of follow-up ultrasonic vibration, the width of unmixed zone was reduced and the macro element distribution was homogenized due to the enhancement of molten convection. The average grain radius was refined from 1.03 μm to 0.55 μm because acoustic pressure in the molten pool reduced critical nucleus size rk and caused grain fragmentation. The higher diffusion coefficient and cooling rate caused by ultrasonic vibration suppressed element segregation, and thus the amount of precipitated phase decreased from 2.15% to 0.62%, which finally improved the intergranular corrosion resistance of weld metal. The load capacity of weld joint was improved by 12.6%, and the micro-hardness of weld metal was also increased, attributing to the grain refinement strengthening. The follow-up ultrasonic vibration process proposed in this paper provided an efficient, convenient and widely applicable process for laser seal welding of dissimilar metals for nuclear reactor pump can end sealing with higher qualities.

First assessment on the microstructure and mechanical properties of gtaw-gmaw hybrid welding of 6061-t6 AA

Abstract Plates of 6061-T6 aluminum alloy of 6.35 mm thick were welded by using the hybrid gas tungsten arc - gas metal arc welding process (GTAW-GMAW) and compare with the conventional gas metal arc welding (GMAW). An ER-5356 filler wire of 1.2 mm in diameter and argon of high purity as protective gas were used in both processes. The aim of the experiments was to assess the effects that yield the GTAW-GMAW welding process on the microstructure and the mechanical properties of the welded joints in the as weld and after artificial aging condition. Heat inputs were set up between ∼ 0.9 kJ/mm and ∼ 1.1 kJ/mm. Plots of the grain size and porosity ratio showed that GTAW-GMAW promoted a grain structure refinement and a reduction of porosity in weld metal. In addition, GTAW-GMAW indicate a reduction on the degradation in the heat affected zone in the as weld condition and a 40 % increase in welding speed. There was observed a major losing of magnesium in weld metal in the conventional GMAW process, this effect reflects on the final mechanical strength and microhardness of weld metal after artificial aging, as less Mg is available to get in solid solution.

Study of Microstructure 304L Austenitic Stainless Steel Weld Deposited by GTAW for Root Pass and SMAW for Filler Passes

In the present experimentation, a 10mm thick austenitic stainless steel plate type 304L is welded using single V-joint configuration and approaching the joint from one side. Back purging has been employed to protect the rear side of the root pass weld metal against oxidation. The root pass has been deposited by gas tungsten arc welding (GTAW) process. The filler passes are deposited by shielding metal arc welding (SMAW) process at 90A and 120A welding currents giving heat inputs of the order of 0.679 and 0.933 kJ/mm respectively while the speed of weld deposition was kept practically constant. The results of experimentation show that the micro-hardness of weld metal and heat affected zone (HAZ) of weldments produced at lower heat input is higher whereas impact toughness value of weld metal and HAZ is lower than that of joints produced at higher heat input. The microstructure of weld metal and heat affected zone developed at lower weld heat input has been observed finer in comparison to that resulted at higher heat input. This has primarily happened due to a higher rate of cooling at low heat input.

Investigation on microstructure and properties of narrow-gap laser welding on reduced activation ferritic/martensitic steel CLF-1 with a thickness of 35 mm

Reduced activation ferritic martensitic (RAFM) steel is chosen as a structural material for test blanket modules (TBMs) to be constructed in International Thermonuclear Experimental Reactor (ITER) and China Fusion Engineering Test Reactor (CFETR). Chinese specific RAFM steel named with CLF-1 has been developed for CFETR. In this paper, a narrow-gap groove laser multi-pass welding of CLF-1 steel with thickness of 35 mm is conduced by YLS-15000 fiber laser. Further, the microstructures of different regions in the weld joint were characterized, and tensile impact and micro-hardness tests were carried out for evaluating the mecharical properties. The results show that the butt weld joint of CLF-1 steel with a thickness of 35 mm was well-formed using the optimal narrow-gap laser filler wire welding and no obvious defects was found such as incomplete fusion cracks and pores. The microstructures of backing layer is dominated by lath martensites and the Heat-Affected Zone (HAZ) was mainly filled with two-phase hybrid structures of secondary-tempering sorbites and martensites. The filler layer is similar to the backing layer in microstructures. In tensile tests, the tensile samples from different parts of the joint all fractured at base metal (BM). The micro-hardness of weld metal (WM) was found to be higher than that of BM and the Heat-Affected Zone (HAZ) exhibited no obvious softening. After post weld heat treatment (PWHT), it can be observed that the fusion zone of the autogenous welding bead and the upper filling beads mainly consist of lath martensites which caused the lower impact absorbing energy. The HAZ mainly included two-phase hybrid structures of secondary-tempering sorbites and martensites and exhibited favorable impact toughness.

The effect of constraint conditions on microstructure and properties of titanium alloy electron beam welding

In the actual production, when the structures are welded, the weld inevitably bears the constraint stress which changes the internal stress state of the weld, and the properties of welding in actual welding structure are different from those in welding sample, so the effect of constraint stress on the microstructure and properties of electron beam welded joint is revealed by the characterization of solidification microstructure of joint under constraint conditions. The results show that the constraint conditions have a great influence on the microstructure, microhardness and properties. The unevenness of the microstructure of the weld increases, the grain size difference increases, the martensite is smaller with a lot of dislocations, and the continuous grain boundary α phase appears. The fusion zone and the heat affected zone consist of fine acicular martensite and residual α with dislocation tangles. The microhardness distribution of the weld is saddle-shaped, and the microhardness of weld metal is the highest. The tensile strength of the constraint welds is 898 MPa, which is higher than conventional EBW joints, and the fracture position is located in the weld. Due to the existence of a large number of dislocations in the martensite under the constraint condition, the hardness and difficulty of slip deformation increase.

Improved microstructure and mechanical properties in gas tungsten arc welded aluminum joints by using graphene nanosheets/aluminum composite filler wires

In the present study, different amounts of graphene nanosheets (GNSs) were added to the 4043 aluminum alloy powders by using the mechanical alloying method to produce the composite filler wires. With each of the produced composite filler wires, one all-weld metal coupon was welded using the gas tungsten arc (GTA) welding process. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. As the amount of GNSs in the composition of filler wire is increased, the microstructure of weld metal was changed from the dendritic structure to fine equiaxed grains. Furthermore, the tensile strength and microhardness of weld metal was improved, and is attributed to the augmented nucleation and retarded growth. From the results, it was seen that the GNSs/Al composite filler wire can be used to improve the microstructure and mechanical properties of GTA weld metals of aluminum and its alloys.

Effect of laser beam position on mechanical properties of F82H/SUS316L butt-joint welded by fiber laser

A dissimilar butt-joint between reduced activation ferritic/martensitic steel F82H and SUS316L austenitic stainless steel was made by 4kW fiber laser and the influence of laser beam position on its mechanical properties before and after post-weld heat treatment (PWHT) was examined at room temperature. From the nano-indentation measurements and the microstructural observations, it is found that the micro hardness of weld metal partially decreases after PWHT by shifting beam position to SUS316L because its phase seems to move from only the martensitic phase to the mixture of austenitic and martensitic phases. In addition, Charpy impact test suggests that the impact energy slightly increases by shifting beam position before PWHT and obviously increases after PWHT due to the release of residual stress. Moreover, the tensile test indicates that the tensile strength of weld metal is higher than that of SUS316L and the fracture occurs at the base metal of SUS316L regardless of laser beam position.

Effect on LY12 Aluminum Alloy Welding Joint Microstructure and Properties with Electron Beam Welding Technical Parameters

LY12 aluminum alloy was welded with vacuum electron beam welding, the effect of welding speed and electron beam current on the weld microstructure and mechanical properties of welding joints were studied, the results were shown that with the increasing of welding speed or decreasing of electron beam current, the grains in weld metal were refined, so the joint strength were increased. When the electron beam current was 18mA, the welding speed was 1000mm/min, the grains of weld metal were the finest, and the tensile strength was 373.2MPa. In addition, the micro-hardness of weld metal was much lower than base metal and heat affected zone, and the heat affected zone had certain softening phenomenon. With the increasing of welding speed or decreasing of electron beam current, the micro-hardness of weld metal was increased respectively.

A new technique for the strengthening of aluminum tungsten inert gas weld metals: Using carbon nanotube/aluminum composite as a filler metal

The effect of multi-walled carbon nanotube (MWCNT) on the mechanical properties of aluminum multipass weld metal prepared by the tungsten inert gas (TIG) welding process was investigated. High energy ball milling was used to disperse MWCNT in the aluminum powder. Carbon nanotube/aluminum composite filler metal was fabricated for the first time by hot extrusion of ball-milled powders. After welding, the tensile strength, microhardness and MWCNT distribution in the weld metal were investigated. The test results showed that the tensile strength and microhardness of weld metal was greatly increased when using the filler metal containing 1.5wt.% MWCNT. Therefore, according to the results presented in this paper, it can be concluded that the filler metal containing MWCNT can serve as a super filler metal to improve the mechanical properties of TIG welds of Al and its alloys.