Nugget Area Research Articles

Effect of Welding Conditions of Spot Welded Zone on the Tensile Strength about Aluminum Alloy (A6061)

It is considered to be available in reducing the weight of automobiles that the aluminum alloy is applied to manufacture them. The spot welding of aluminum alloys is difficult because of high welding current and small electrical resistance. It is necessary to clarify the relation between the nugget formation and the welding conditions. In this study, the relation between the spot welding conditions and the nugget form was investigated, and the joint strength and the fracture mode were investigated. As a result, the nugget area and micro cracks in the HAZ were increased with increase of the welding current. It is found that in case of aluminum alloys the formation of micro cracks was a main factor of reduction of maximum tensile load of the welded zone.

Mechanical Properties Investigation of Multi-Lap Stainless Steel Sheets

The mechanical testing and microstructers for austenititc stainless steel have been carried out to indicate the effect of the localized heating on the spot welds. The results indicated that the increasing of the heating will increase the tensile shear strength rapidly up to the expulsion point. Therefore, the hardness increases with the increasing of the weld nugget area. Hence, the fracturing tendencies have been observed inside the nugget. Nevertheless, the outer surface cracking is developed by adding a thin layer of pure metals between the two stainless steel 304L sheets. It was shown that the addition of pure metals, 3-lap sheets decreases the joint strength as compared with the 2-lap joints for the same parameters. The effect of micro cracking and the intensive brittleness decreases the joint strength. The excessive cracking was observed in 3-lap as compared with the 2-lap joint.

Parameters optimization in FSW of polypropylene based on RSM

Purpose – The purpose of this paper is to weld polypropylene (PP) material by friction stir welding (FSW) process. The input process parameters considered were: tool pin profile, feed rate and tool rotational speed and the process output characteristics were tensile strength, Shore-D hardness, Rockwell hardness, Izod strength, Charpy strength and nugget area. Design/methodology/approach – Optimization of process parameters were carried out based on response surface methodology (RSM) and significant parameters were obtained by performing analysis of variance (ANOVA). Findings – The optimized results were the threaded pin profile for feed of 60 mm/min and tool rotational speed of 1,500 rpm. A confirmation test was carried out to verify the optimized results. Originality/value – In this paper, the process parameters were optimized based on RSM. This is newly adopted optimization techniques in the FSW process of PP materials and also it gives better results.

Microstructure and mechanical properties of dissimilar Al–Cu joints by friction stir welding

Dissimilar friction stir welding between 1060 aluminum alloy and annealed pure copper sheet with a thickness of 3 mm was investigated. Sound weld was obtained at a rotational speed of 1050 r/min and a welding speed of 30 mm/min. Intercalation structure formed at the crown and Cu/weld nugget (WN) area promotes interfacial diffusion and metallurgical bonding of aluminum and copper. However, corrosion morphology reveals the weak bonding mechanism of internal interface, which causes the joint failing across the interface with a brittle–ductile mixed fracture mode. The tensile strength of the joint is 148 MPa, which is higher than that of the aluminum matrix. Crystal defects and grain refinement by severely plastic deformation during friction stir welding facilitate short circuit diffusion and thus accelerate the formation of Al4Cu9 and Al2Cu intermetallic compounds (IMCs). XRD results show that Al4Cu9 is mainly in Cu/WN transition zone. The high dislocation density and formation of dislocation loops are the major reasons of hardness increase in the WN.

Effect of tool pin eccentricity on microstructure and mechanical properties in friction stir welded 7075 aluminum alloy thick plate

Four different tools with the pin eccentricity of 0.1mm, 0.2mm, 0.3mm and 0.4mm were designed to friction stir weld 10mm thick AA7075-O plate. The effect of pin eccentricity on microstructure, secondary phase particles transformation and mechanical properties of the joints was investigated. The results show that the nugget area (ANZ) increases firstly and then decreases with increasing the pin eccentricity. When the pin with 0.2mm eccentricity is applied, the ANZ is the largest; meanwhile the grains size is the smallest which is about 3μm and secondary phase particles are the most dispersive in nugget zone compared with other tools. While the grains are coarsened to 7–11μm as the eccentricity is more than 0.4mm, some coarse hardening particles get to cluster in the thermo-mechanically affected zone. The joints produced by the pin with 0.2mm eccentricity perform the highest tensile strength and elongation, which is attributed to better interfaces, finer grains and more dispersive secondary phase particles.

Characterization of Mechanical Properties in Processed Friction Stir Welded High-strength Aluminum Alloy Blanks

Within this investigation mechanical properties of friction stir welded high strength aluminum blanks are determined. The recrystallization behavior of base material and weld nugget material are analyzed regarding prestraining in a cold upsetting and rolling process. Finally the properties of natural and artificial aged specimen are compared in uniaxial tensile tests. It can be shown that the prestraining has a significant effect on the resulting grain size after solution heat treatment in the weld nugget. Recrystallization and the evolution of a coarse grain structure in the nugget leads to a reduced strength and ductility for both ageing conditions. For the process design of manufacturing tailored aluminum blanks the prestrain dependent recrystallization and part property evolution has to be considered especially for the weld nugget area.

Comparison of microstructure and mechanical properties of conventional and refilled friction stir spot welds in AA 6061-T6 using filler plate

Friction stir spot welding with refilling by friction forming process (FSSW-FFP) was successfully modified using filler plate. Both of this new refilling technique and conventional friction stir spot welding (FSSW) process were used to weld Al 6061-T6 lap shear specimens and the results were compared. Effects of tool rotational speeds on mechanical and metallurgical properties in both the cases were studied. Static shear strength of refilled weld samples was found to be better than those welded by conventional FSSW process at all tool rotational speeds. This is explained in terms of effective increase in cross-sectional area of weld nugget due to addition of more material from filler plate, thereby eliminating the probe hole. Failure mechanisms were discussed and fracture surfaces were analyzed through scanning electron microscopy (SEM). The hardness profile of the welds exhibited a W-shaped appearance in both the processes and the minimum hardness was measured in the HAZ.

광원 펄스와 위상잠금 적외선 열화상을 이용한 점용접부의 건전성 평가 연구

The non-destructive testing using infrared thermography is extended to a variety of industries and non-destructive testing of welds using infrared thermography is also in progress in various ways. Currently, a non-destructive testing of electrical resistance spot welds which is mainly used is Radiography Testing. This study detected area of spot welds nugget using optical-infrared thermography. In the results, it is possible for detecting defects of nugget in a short period of time using pulse-infrared thermography.

Microstructure and Mechanical Properties of Refilled Friction Stir Spot Welding of Commercial Pure Aluminium

Aluminium and magnesium alloys are expected to make considerable contributions in reducing the weight of automobiles as they are increasingly used as an alternative to steel; improving fuel economy and vehicle performance while simultaneously reducing emissions. Higher electrical and thermal conductivities of these materials make them difficult to weld using existing resistance spot welding leading to high energy consumption. Friction stir spot welding has proven to be a better alternative to weld these materials. But a probe hole left behind is the main problem in conventional Friction Stir Spot welding (FSSW). In the present work a new method has been developed to refill the probe hole using an additional filler plate known as Refill Friction Stir Spot welding (RFSSW). This new refilling technique and the conventional FSSW process were both used to weld commercially pure aluminium lap shear specimens and the results were compared. The effect of tool rotational speed on mechanical and metallurgical properties were studied in both cases. Static shear strength of RFSSW weld samples was found to be better than conventional FSSW process at higher tool rotational speed. This is explained in terms of effective increase in cross sectional area of weld nugget due addition of more material from the filler plate thereby eliminating the probe hole.

Finite Element Analysis for Mechanical Characteristics of Resistance Spot Welding Process with Three Sheets Assemblies

This project is focused on the finite element (FE) analysis for mechanical characteristics of resistance spot welding (RSW) process with three sheets stack up instead of conventional two sheets assemblies because of its wide application in automobile industry. It is proved that the protuberances region localized in the nugget area induced in the welding process are more inclined to have fatigue failure such as cracks and fracture. Local stress and strain distributions for three sheets stack up under quasi-static tension load are investigated by both experiments and FE analysis with commercial software code ANSYS and NASTRAN. The high stress/strain value is concentrated at the edges of nugget instead of nugget center from cross section view and stress/strain distribution at the center region of the weld nugget is relatively low. The FE analysis has effectively verification with the experiments results.

The Influence of Process Parameters on Microstructure and Mechanical Properties of Friction Stir Welded Al 5083 alloy Lap joint

Recently the aircraft and military industries widely have been using aluminum alloys particularly because of their fine strength to weight ratio. However in compare with steels they represent welding difficulties and also lower ductility. In last years it has been observed that Friction Stir Welding (FSW) method represents better microstructure and mechanical properties than conventional methods in welding aluminum alloys. In this study experiments were performed to investigate the effects of FSW process parameters including rotational and welding speed on the microstructure and mechanical properties of aluminum 5083 alloy in lap joint welding and different joint defects were analyzed. It was observed that the nugget area had the best grain size and also higher hardness in compare with the other welding areas. Also the best joint properties were achieved at the rotational speed of 825rpm and welding speed of 32mm/min.

Characterization of microstructure and deformation behaviour of resistance spot welded AZ31 magnesium alloy

Resistance spot welds were prepared on 3 mm thick sheets of continuous cast and rolled AZ31 magnesium alloy. The microstructure and composition analysis of weld nugget, heat affected zone (HAZ) and base metal were examined using optical and scanning electron microscopy (HR-SEM and EDS/X). The resistance spot welded magnesium alloy joints consist mainly of weld nugget and HAZ. The nugget contains two different structures, i.e. the cellular-dendritic structure at the edge of the nugget and the equiaxed dendritic structure in the centre of the nugget. The structure transition is attributed to the changes of solidification conditions. In the HAZ, grain boundary melting occurred and grain boundaries became coarse. It has been shown that hardness reduction in the weld nugget and HAZ compared with base metal is evident due to dendritic microstructure and grain growth, respectively. The results showed that spot welded joints have failed in interfacial mode under torsion and tensile–shear loading conditions. Digital image correlation during tensile–shear testing showed that low surface strains occur in the interfacial failure mode, because fracture and deformation happened primarily in the nugget area.

Effect of heat input on weld bead geometry of submerged arc welded ASTM A709 Grade 50 steel joints

A series of measurements was carried out on specimens of submerged arc welded plates of ASTM A709 Grade 50 steel to determine how variation in heat input achieved using single and double wires affected bead reinforcement, bead width, penetration depth, contact angle, heat affected zone (HAZ) size, deposition area, penetration area and total molten area. The level of dilution and different melting efficiencies were calculated and their variation with heat input was analyzed based on the acquired measurements. The cooling time from 800 to 500°C was also related to various weld bead characteristics (e.g., total nugget area, heat transfer boundary lengths, bead width-to-depth ratio, and nugget parameter). The bead reinforcement, bead width, penetration depth, HAZ size, deposition area and penetration area increased with increasing heat input, but the bead contact angle decreased with it. The electrode melting efficiency increased initially and then decreased with increasing heat input, but the plate melting efficiency and percentage dilution changed only slightly with it. Cooling time exhibited a very good linear relationship with the total nugget area, heat transfer boundary length, and nugget parameter.

Non-Contact Measurement of Nugget Size of Spot Welding Using Focused Air-Coupled Ultrasound

Spot welding is widely used in the various fields of engineering and industries. Since the size, shape and mechanical properties of a nugget which is a zone melted and re-solidified during welding are closely related to the strength of the welded structure, quantitative evaluations of them are strongly required. In this work, an air-coupled ultrasound technique with focused transducers has been used for non-contact measurements of spot welds of steel plates. One-dimensional scanning in transmission configuration using a pair of focused air-coupled ultrasonic transducers operating with tone burst waves at 0.3 MHz is performed to obtain the amplitude profile of the transmitted ultrasound through the nugget area of a spot weld. A simple method for determining the nugget size from the profile of the transmitted ultrasound is proposed. To verify the validity of the method, calibration samples which imitate spot welds having different sizes of nuggets are prepared and used for demonstrating nugget size determinations. In addition, the proposed method has been applied to evaluate several spot welds fabricated with different electric currents (5 kA – 9 kA).

Numerical Analysis of Transport Phenomena in Resistance Spot Welding Process

Resistance spot welding (RSW) is a very complicated process involving electromagnetic, thermal, fluid flow, mechanical, and metallurgical variables. Since weld nugget area is closed and unobservable using experimental means, numerical methods are generally used to reveal the nugget formation mechanism. Traditional RSW models focus on the electrothermal behaviors in the nugget and do not have the ability to model mass transport caused by induced magnetic forces in the molten nugget. In this paper, a multiphysics model, which comprehensively considers the coupling of electric, magnetic, thermal, and flow fields during RSW, temperature-dependent physical properties, and phase transformation, is used to investigate the heat and mass transport laws in the weld nugget and to reveal the interaction of the heat and mass transports and their evolutions. Results showed that strong and complicated mass transport appears in the weld nugget and substantially changed the heat transport laws and, therefore, would be able to substantially affect the hardening, segregation, and residual stress of the weld. Compared with the traditional models which could not consider the mass transport, the multiphysics model proposed in this paper could simulate the RSW process with higher accuracy and more realities.

Corrosion Fatigue Behavior of Resistance Spot Welded Dissimilar Metal Welds between Carbon Steel and Austenitic Stainless Steel with Different Thickness

Corrosion fatigue behavior of resistance spot-welded dissimilar metals with significant difference in thickness between carbon steel and austenitic stainless steel has been studied. Carbon steel SS400 with thickness of 3.0mm and 1.0mm thick- austenitic stainless steel SUS304 were lap joined using resistance spot welding. The welding conditions used including weld current, weld time and electrode force were 4.7 kA, 20 cycles and 6kN respectively. Corrosion fatigue tests were carried out at a room temperature in seawater environment with the salinity of 34.5g/L and pH of 8.0. A sinusoidal wave input with a constant stress amplitude was selected whereas the stress ratio and frequency used were 0.1 and 8Hz respectively. Fatigue tests were also conducted in air as a comparison. Other experiments such as metallographical examination, microhardness measurement, electrochemical tests and nugget area evaluation using neutron radiography were performed for supporting analysis. Results show that corrosion fatigue strength of resistance spot welded in sea water is lower than that performed in the air. The endurance limit of fatigue conducted in air is 32.6MPa whereas corrosion fatigue samples at this stress fail at about 400,000 cycles. It seems that the hydrogen enhanced plasticity mechanism that tends to ease the generation of dislocations is the cause of corrosion fatigue strength weakening.

Visualization of Fluid Flow and Heat Transfer in Resistance Spot Weld Nugget

Resistance spot welding is a very complicated process involving electro-magnetic, thermal, fluid flow, mechanical and metallurgical variables. Since weld nugget area is close and unobservable with experimental means, numerical methods are mainly used to reveal the nugget formation mechanism. So far, heat transfer behaviors in the weld nugget have been systematically studied with traditional electro-thermal model, however, the model cannot model the fluid flow caused by induced magnetic field in the molten nugget. In this paper, a multi-physics model, which comprehensively considers the coupling of electric, magnetic, thermal and flow fields during RSW, is used to investigate the fluid flow and heat transfer laws in the weld nugget. Results show that molten metal in the nugget makes high speed rotation motion in four cores, moreover, the rotation motion significantly changes the profile of the nugget and the thermal field evolution, compared with the traditional electro-thermal model. Because the fluid flow and heat transfer jointly determines the crystallization process and final microstructure, as a result, when predicting crystal growth process, the effects of the fluid flow during resistance spot welding should be considered in order to obtain a more accurate prediction results.

Non-Contact Determination of Nugget Size of Spot-Welding Using Focused Air-Coupled Ultrasound

Since the size and shape of a nugget of a spot weld are closely related to the bonding strength of the weld, their quantitative evaluations are very important to improve the reliability of the welded structures. In this work, a focused air-coupled ultrasound technique has been used for non-contact measurements of spot welds of steel plates. One-dimensional scanning in transmission configuration using a pair of focused air-coupled ultrasonic transducers operating with tone burst waves at 0.3 MHz is performed to obtain the amplitude profile of the transmitted ultrasound through the nugget area of a spot weld. A simple method for determining the nugget size from the amplitude profile is proposed. The validity of the method is verified using a calibration sample which imitates a spot weld. The proposed method has then been applied to the evaluations of spot welds fabricated with different electric currents.

Mechanical Properties of Friction Stir Welded Mg/Mg‐ and Mg/Al‐Joints

AbstractIn a mobile world weight reduction is a predominant target of innovative products. In this context appropriate joining techniques are necessary for the integration of lightweight metals in complex mechanical components. Friction stir welding (FSW) is a newly established well suited process to realize high‐quality lightweight metal joints in solid state. In a research project of WKK the friction stir weldability of similar joints using die casted AZ91‐Mg‐alloy and MRI‐Mg‐alloys was investigated. Additionally the joining of hybrid joints between AZ91 and AA5454 aluminum alloy was performed. To describe and optimize the FSW‐process the welding temperatures and welding forces were recorded online during the process. The investigations of the monotonic properties of AZ91/AZ91‐joints and MRI/MRI‐joints yielded in tensile strength values at the level of the parent materials. For dissimilar joints an extreme increase of the nugget hardness was measured. By SEM investigations and EDX element mappings it could be proved that this is caused by intermetallic phases positioned as thin interlayers in the contact area between the Mg‐ and the Al‐alloy. As a consequence, in hybrid joints failures occur predominantly along these interlayers. Finally, for similar and dissimilar welds corrosion experiments in 5 mass% NaCl solution were carried out. The investigations showed that the nugget area was more susceptible to corrosion then the base material. To understand the corrosion behavior the affected areas were analyzed using SEM and EDX.

Process Parameters in Resistance Projection Welding for Optical Transmission Device Package

The effects of main process parameters and electrode materials on joint quality (charging voltage and operating force) were investigated using detailed metallurgical examination and the helium leak test. The electrode materials used for resistance projection welding were brass and Cr-Cu alloy. The TO-Can components (cap and header) were nickel-coated SPCC steel. The results indicated that when the operating pressure increased, the electrode displacement increased, causing expulsion and distortion of the welds. The nugget area increased with the increase of charging voltage; however, it decreased with the increase of operating pressure. Results from the optical microscopy analysis showed that a larger acceptable welding range was achieved by using Cr-Cu electrodes. TO-Can in the acceptable and expulsion range successfully passed the helium leak rate of less than 5 × 10−8 mbar L/s. For commercial purposes, where dimensions have to be exact and without deformation, the TO-Can components produced in the expulsion zone cannot be used.