Microhardness Of Welded Joints Research Articles

Optimization and Improvement of the Projection Welding of Nut Based on Regression Analysis

Since it has the advantages of high production efficiency, no shunting effects, and the ability to arrange solder joints on narrow locations without the limitation of point distance, projection welding of nut has been widely used in the automotive industry. This paper presents a new welding quality prediction and analysis framework by using regression analysis techniques. The relationship between the welding parameters (welding time, welding current and electrode force) and the Pull-out load of the M6 welded square nut and the 1.5 mm thick pickled hot-rolled steel was obtained by multiple nonlinear regression analysis. The influence and interaction of welding parameters on the Pull-out load are discussed. Using this regression model, a better combination of process parameters can be obtained. The mechanical properties, microstructure and microhardness of welded joints were also investigated.

Influence of the heating force in rotational friction welding on mechanical properties and tensile fracture mechanism of dissimilar welded joints of 30KhGSA and 40KhMFA steels

This article presents the results of evaluating the effect of heating force, as one of the parameters of rotational friction welding, on the mechanical properties and mechanism of tensile failure of dissimilar welded joints of medium-carbon steels 30KhGSA and 40KhMFA. The results of studies of the microstructure and microhardness of welded joints are presented. The fracture mechanism of welded specimens during tensile testing was evaluated on the basis of strain distribution maps obtained by the digital image correlation method and the results of fractographic analysis. The features of the development of deformation and failure of welded joints obtained at different heating forces are shown. From the point of view of the equal strength of the structure with a welded joint the optimal values of this parameter of rotary friction welding for joining steels 30KhGSA and 40KhMFA are recommended.The reported study was funded by RFBR according to the research project № 20-38-90032.When conducting mechanical tensile tests and studying the distribution of deformation fields, equipment was used that is part of the Plastometriya collective centre of the IES named after E. S. Gorkunova of the Ural branch of the RAS

Optimization of friction stir welding process parameters using MCDM method

Friction Stir Welding (FSW) is categorized into a solid-state welding process which is preferred to join aluminum-based materials effectively. Generally, aluminum-based materials are welded using solid state welding than fusion-based welding due to the chance of hot cracking, loss of elements and porosity. Process parameters and its selection in FSW process are important and it leads to efficient of weld quality. Taguchi concept is a standard optimization procedure but it has a limitation of not capable to solve multi objective problems simultaneously. Multi Criteria Decision Making (MCDM) method can be used for solving multiple objectives simultaneous effectively. Al-6061 T6 alloy is used as workpiece and carbon steel, H13 tool steel and high carbon high chromium steel is used as tool materials. The important process parameters considered are rotational speed of tool and welding speed. Response parameters selected are tensile strength and microhardness of welded joints. Process parameters are optimized using MCDM method and the optimum values obtained are rotational speed of 700 rpm and welding speed of 35 mm/min. It is understood that better tensile strength and microhardness of FSW joints at optimized condition due to adequate material flow, fine grain size and pulsating action. MCDM method has simple calculation procedure and easier solving methodology for machining parameters optimization.

Effect of CMT Welding Heat Input on Microstructure and Properties of 2A14 Aluminum Alloy Joint

Cold metal transfer (CMT) welding is an attractive welding technology for thin sheet aluminum alloys because of its low heat input, arc stability and spatter-free behavior during the welding process. The present research is mainly concerned with the effect of different heat input on microstructure and mechanical properties of CMT welding 2A14 aluminum alloy in 3 mm thickness. The results indicate that a welded joint with good quality can be achieved when the welding current is 105 A and welding speed is 8 mm/s. The weld width and porosity gradually increase along with the constantly increasing welding heat input. The center of the welded joint consists of a large number of fine equiaxed dendrites, and the gray matrix is uniformly distributed accompanied by a large number of dots and blocks as a white second phase, corresponding to the composition of the Al2Cu phase. The microhardness of welded joints under different welding heat input maintains relative stability and presents a certain softening degree; the base material is the highest, followed by the heat-affected zone.

Investigation on shearing strength of resistance spot-welded joints of dissimilar steel plates with varying welding current and time

The present research investigated the effects of welding current and welding time on the shearing strength of resistance spot-welded joints of low carbon steel and stainless steel plates. The macro characteristics, microstructure and micro-hardness of welded joints were also examined. It was found that the welded joints produced with a welding current of 10 kA and welding time of 80 ms showed the highest shearing strength. The diameter of welded joints and nuggets increased with increasing welding current and welding time. For evaluation of the microstructure, different regions including the nugget, coarse heat-affected zone, fine heat-affected zone and base materials were observed within the welded joints. Also, the nugget and coarse heat-affected zone showed higher hardness than the fine heat-affected zone and base materials due to the presence of martensite. The findings obtained in this research are applicable in the development of resistance spot welding processes for joining dissimilar steel plates.

Mechanical behaviors of electron beam welded titanium alloy up to very high cycle fatigue under different process conditions

The mechanical behavior of electron beam welded joints for titanium alloy has been investigated in static and cyclic loading up to very high cycle fatigue. It can be concluded that a higher welding voltage parameter and optimal heat treatment condition in combination will produce higher static and cyclic properties of titanium alloy welded joints. The metastable martensite α′ structures in the β grains of the fusion and heat-affected zones are wholly decomposed into small lamellar α phases, forming α + β phases through the post-weld heat treatment (PWHT). Hence, the welded joints by PWHT could transform the “concave” shape microhardness distribution into “convex” shape distribution. The fatigue cracks are initiated from the internal pores of the material in very high cycle fatigue regime. The higher voltage parameter applied to the welding process could reduce the density of pores in the material, which is in favour of the fatigue life of the welded joints. • A higher voltage and optimal heat treatment in combination produce higher mechanical properties of welded joints. • Microstructure and microhardness of welded joints were analyzed before and after heat treatment. • The higher voltage reduced the pores density in the welded joints, which improved fatigue life.

Microstructure and alloy element distribution near the fusion line of aluminum alloy 6061 in laser wire-filling welding

Aluminum alloy 6061(AA6061) sheets of 4 mm in thickness are joined by laser wire-filling welding (LWFW) using the ER4047 welding wire. Microstructure and alloy element distributions near the fusion line are characterized and are investigated by optical microscope, scanning electron microscope, energy dispersive spectrometer. The results showed that the well-formed welded joints are obtained with a few thermal cracks near the fusion line. The coarse grain and a reduction in the weight ratio of magnesium to silicon can be observed, when the welding speed decreases under constant laser power. The thermal crack is caused by the decrease of the weight fraction of magnesium and the proportion of silicon content has an effect on the microhardness of welded joints. By properly controlling the welding speed, the various properties of AA6061 LWFW joints can be balanced.

Welding condition & microstructure of friction stir welded AA 6061-T6 and AZ31B

Dissimilar friction stir welding between 6061-T6 Al alloys to AZ31B Mg alloys with a plate thickness of 6 mm was investigated. Defect-free welds were obtained at a different rotational speed ranging from 400 to 700 rpm with welding speed of 0.5–0.8 mm/sec, respectively. The influence of welding speed and rotational speed was investigated to reveal the microstructure growth and microhardness of weld joint that displays tortuous interface as well as intermetallic compounds. Irregular distribution of microhardness was found due to complex microstructure. Intermetallic compound Al3Mg2 and Al12Mg17 were revealed by energy dispersive spectroscope (EDS) analysis. Compared to the base metal value of maximum microhardness was double in the stir zone.

Multi-response optimization of friction stir spot welded joint with grey relational analysis

This study presents Taguchi grey based optimization of process parameters such as tool tilt angle, tool rotational speed, dwell time and tool pin profile and their effect on lap shear strength and microhardness of AA6082-T6 and AA6061-T6 friction stir spot welded joint. Taguchi's L27 orthogonal array design is used for maximizing both responses. Analysis of variance was performed to find the effect on individual parameter on both responses. The joints were metallurgically characterized through scanning electron microscopy, optical microscopy and X ray diffraction. Microstructures and residual stresses at weld region were analyzed. An optimum combination of parameters was determined as tool tilt angle at level 3 (20), tool rotational speed at level 3 (2125 rpm), dwell time at level 3 (15 s) and tool pin profile at level 1 (Cylindrical Threaded). Finer and uniform grain structure at stir zone improves the tensile shear strength and microhardness of welded joints.

Influence of Post-Weld Heat Treatments on Microstructure and Mechanical Properties of Laser Beam Welded 2060-T3/2099-T3Al-Li T-Joints

The durable structure and robustness of T-joints in the panel materials for civil aircraft are a crucial matter of importance. In this work, the impact of the post-weld heat treatments (PWHTs) on the microstructure and mechanical properties of laser beam welded T-joints of 2060-T3/2099-T3 Al-Li alloy was analyzed. Heat-treatment of the laser beam welded T-joints was carried out in two different ways, namely, solution treatment and artificial aging (STAA) at varied duration and only artificial aging (AA) at varied duration. The microstructure and mechanical properties of the heat-treated joints were investigated using metallographic and scanning electron microscopic images, micro-hardness test, and tensile test, respectively. The results showed that, in cases of STAA, the eutectic structures on the grain boundary were partially dissolved via solution treatment (ST), and increased dispersed precipitation of the second phase in matrix resulted in significant dispersion strengthening, as well as enhanced strength and plasticity. In contrast, in the AA process, alloy elements in the matrix continued to segregate towards the grain boundary, resulting in significant grain boundary strengthening, enhanced strength, and decreased plasticity. Additionally, joint fractures were micro-porous aggregation transgranular ones in the fusion zone (FZ). The joints treated by STAA exhibited excellent plasticity compared with those treated by AA. Furthermore, the micro-hardness of welded joints treated by AA was higher than that of those treated by STAA. Indeed, the tensile strength of joints treated by STAA and AA ranged from 405 to 475 MPa, which was 81–95% of the base metal 2060-T8, though the elongation of joints treated by STAA was superior to the counterpart AA.

Influence of post-weld heat treatment on microstructure and mechanical properties of laser beam welded 2195 Al–Li alloy

2195 Al–Li alloy is welded by using laser beam welding (LBW). Subsequently, the welded joints are treated by solution treatment at 520 °C for 1 h, then aging treatments with different procedures. The influence of post-weld heat treatment (PWHT) on microstructure and mechanical properties of the welded joint is systematically investigated. Optical microscope (OM), scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), and x-ray diffractometer (XRD) are used to characterize the microstructure of joints respectively. The tensile strength and microhardness of welded joints before and after PWHT are evaluated respectively. Results show that, after post-weld double aging treatment (HT3), the tensile strength of welded joint is 485.2 MPa, which is 89.03% of that of base metal. Microstructural analysis indicates that the fine equiaxed grain zone (EQZ) near fusion line disappears after HT3. The precipitation of strengthening phases such as T1(Al2CuLi) phase is promoted by PWHT both near grain boundaries and in Al matrix. Moreover, the microstructure of weldment is refined after HT3, thus the ductility of welded joint is improved to a certain extent.

Effect of molybdenum addition on microstructure and mechanical properties of plain carbon steel weld

The present investigation has two main objectives; first is optimization of welding process parameters of submerged arc welding (SAW) using Taguchi philosophy and second is to improve the mechanical properties such as strength and microhardness of weld joint by alloying with varying amounts of molybdenum. For optimization of welding process, parameters Taguchi philosophy have been applied on a mild steel plate (AISI C- 1020) of 10 mm thickness with 60o groove angle with arc voltage and welding speed as variables and bead width as output variables. A mathematical relationship between bead width, arc voltage and welding speed has also been found using multiple regression analysis for the present base metal plate geometry. After optimizing welding parameters, molybdenum has been added individually to the welding area in varying percentages. The properties of alloyed and unalloyed weld metal bead are compared. The mechanical characterization of weld has been done in terms of microhardness, tensile strength, whereas microstructural characterization has been performed using optical microscopy, XRD and EDS. The presence of molybdenum resulted in bainite structure in weld bead having a refined grain structure, enhancement in tensile strength and microhardness. The XRD results showed the formation of molybdenum carbides justifying the increase in microhardness value.

Influence of Friction Stir Welding Parameters on the Mechanical Properties of EN AW-7075 Weld Joints

The paper deals with the friction stir welding (FSW) of the high strength EN AW 7075-T651 aluminium alloy with the aim to analyze the influence of welding parameters on the mechanical properties of Al-weld joints. FSW represents relatively novel solid-state technology of material joining which can be successfully applied for welding of several metallic alloys including the high-strength aluminium alloys that are hard to weld by conventional fusion welding processes. In cooperation with VÚZ - PI SR Bratislava, nine experimental weld joints of samples with dimensions of 300 × 150 × 10 mm were prepared using the welding machine of the FSW-LM-060 type and different parameters of welding – the welding speed from 60 to 120 mm/min and the tool rotation rate from 600 to 1000 rpm in clockwise direction. The quality of weld joints was evaluated by static tensile tests and micro-hardness measurements. According to obtained results of tensile testing, the average values of ultimate strength of weld joints are by 32.2 % lower comparing with the ultimate strength of the base material. On the other hand, the ductility increased by 7.2 %. The highest micro-hardness of weld joints at the level of 129 HV was measured in thermo-mechanically affected zone on the retreating side.

Diffusion Bonding between AZ31 Magnesium Alloy and 7075 Aluminum Alloy

A study on vacuum diffusion bonding between as-extruded AZ31 magnesium alloy and 7075 aluminum alloy was carried out according to atomic diffusion theory. Recrystallization annealing was used for grain refinement of AZ31 magnesium alloy and 7075 aluminum alloy before the diffusion welding. The quality of the bonding joints was checked by shear test, micro-hardness test and microstructure analysis. Experimental results showed that the welding temperature and holding time have a great effect on the joint shear strength. The maximum of shear strength was 38.41MPa under the temperature of 470°C and the holding time of 60min. The result of micro-hardness measurement showed that the micro-hardness of welded joints was maximum. Three kinds of intermetallic compounds, Mg2A13, MgAl and Mgl7Al12, formed at the interfacial transition zone at 470°C.

Microstructure and Properties of 0.2mm Thick Sheet Titanium Alloy by Micro-Laser Welding

0.2mm thick titanium alloy sheet was butt-welded using micro impulse laser, influnce of the different processing parameter on the surface and cross-section morphology of welded joint was studied , testing the mechanical properties of joints. The result show that argon as a shielding gas, 0.2mm thick titanium alloy to the laser as heat source can be successful butt welding with process parameters of the pulse power 8.8W, pulse width 2.9ms, pulse frequency 7.0HZ, and forming a good welded appearance, the tensile strength and microhardness of welded joints was higher than the base metal. By the needle-like martensite α 'phase composition of the basket-like structure located in the center of the weld.

Numerical Simulation on Temperature Field of Electron Beam Welding of Magnesium Alloy and Study on Properties and Microstructure of Joint

Magnesium alloys are being increasingly used in automotive and aerospace structures. In this study, welding of AZ61 magnesium alloy with 10 mm thickness was carried out using vacuum electron beam welding (EBW). By using the finite element model and the 3D moving double ellipsoid heat source model, numerical simulation method was employed to study the influence of the electron beam current on the temperature field of welding process and weld penetration. The microstructure and microhardness of weld joint obtained by the optimized vacuum EBW process had been investigated in detail. The results show that the numerical simulation result basically matches the experimental result. A favorable joint had been obtained by EBW for AZ61 magnesium alloy, in which heat affected zone was not evident, the fusion zone (FZ) consisted of fine-equiaxed grain. The weld hardness was greater than that of the base metal.

Cracking of Welded Joints of Cast and Deformed Titanium Alloy VT5

The macro- and microstructure and microhardness of welded joints of titanium alloy VT5 are investigated. Fracture surfaces are studied and fractional analysis of hydrogen in cast metals is performed. Suggestions are put forward as to the causes and mechanisms of formation of cracks in a weld joint of a forging and a casting from alloy VT5. Places of crack initiation and subcritical growth are determined.

Ultrasonic shock treatment of welded joints

We develop a method of ultrasonic shock treatment of welded joints. It is shown that ultrasonic shock treatment increases the yield stress and microhardness of welded joints and decreases the probability of fatigue fracture. We study the microstructure of welded joints after ultrasonic shock treatment and propose a theory of accumulation of strains in the process of treatment.