Mechanical Properties Of Joints Research Articles

Effect of Ag interlayer on friction torque, mechanical properties and microstructure of large diameter aluminum/steel joints by continuous drive friction welding

The large diameter aluminum/steel continuous driven friction welding component is prone to overload of the main motor due to high friction torque in the welding process. Therefore, multistage friction is used in industrial production to avoid overloading the main motors. However, multistage friction usually increases the heat input in the welding process and leads to the formation of thick and heterogeneous FeAl intermetallic compounds at the welding interface, which degrades the mechanical properties of the joints. Adding an Ag interlayer to the aluminum/steel interface can reduce the friction torque in the welding process, inhibit the interdiffusion of FeAl elements and reduce the thickness of FeAl intermetallic compounds. In this study, Q235 low-carbon steel rods (Diameter of weld end = 120 mm) with/without Ag interlayer and 1060 pure aluminum rods (Diameter of weld end = 90 mm) were welded by continuous drive friction welding. Voltage and Current of Major Motor (VCMM) in the welding process were processed and analyzed. The effects of the Ag interlayer on friction torque, mechanical properties of the post-weld joint and microstructure at the welding interface were analyzed. The research shows that the Ag interlayer can effectively reduce the initial peak torque and joint temperature in the welding process. The mechanical properties and intermetallic compound thickness of the post-weld joint still exhibit heterogeneity along the radial direction. The strength and toughness are significantly improved in the region of 0.5– 0.8R from the center, which is because the Ag2Al and Ag3Al phases with better toughness are formed in this region due to the change of the flow form of the interfacial viscoplastic metal by the Ag interlayer.

Investigation on clinch riveting process with different material combinations

Clinch riveting is a new joining process originating from clinching. The presence of rivets greatly enhances the shearing load of joints. However, conventional rivet is deformable, which may increase technological intricacy consequently. In this article, clinch riveting with rigid rivets was proposed, and the effects of sheet material combinations on the mechanical properties of joints were researched. Four sheet material combinations, involving two kinds of aluminum alloy (AA5052 and AA1060), were utilized to produce the clinch riveted joints. The joining quality was evaluated in four aspects: tensile load, shearing load, failure mode, and absorbed energy in shearing tests. Tensile and shearing tests were implemented to obtain the static load of joints. Results showed that both sheet materials and the geometrical parameters of joints were key factors determining the mechanical properties of joints. During the joining of different materials, the joint with a high-strength sheet on the top exhibited greater static load and absorbed energy than the joint with a low-strength sheet on the top. Neck fracture, button separation, and mixed failure could be observed in tensile tests. In shearing tests, all joints failed at the neck parts.

Microstructure evolution and interfacial bonding mechanisms of ultrasonically soldered sapphire/Al dissimilar joints using Sn-based solders

Sapphire and 5A06 Al were ultrasonically soldered with Sn9Zn, SAC305 alloy solders and NiCu alloy foam added Sn-based composite solders, respectively. The microstructure and mechanical properties of joints were investigated and the interfacial bonding mechanism was analyzed. Cracks were observed at the sapphire/Sn matrix interface in joints soldered with alloy solders, which were disappeared in the joints soldered with composite solders. In the joint using NiCu–Sn9Zn composite solder, the solder seam was uneven and Al3Ni intermetallic compound (IMC) layer was formed on the surface of NiCu alloy skeletons. While in the joint using NiCu-SAC305 composite solder, fine particles of (Ni,Zn)3Sn4 were largely formed and homogeneously distributed in the solder seam. An amorphous Al2O3 transition layer was formed at the sapphire/Sn matrix interface, and Zn enrichment was found at the Sn matrix/amorphous Al2O3 interface. The action mechanism of Zn was analyzed by first-principles calculation. The joints soldered with NiCu-SAC305 composite solder exhibited the highest shear strength of 74.42 MPa, the shearing failure mainly happened in the soldering seam.

Joint formation and mechanical properties of ultrasonic-assisted transient liquid bonding of dissimilar Al/Mg with a Zn interlayer in air

In this work, ultrasonic-assisted transient liquid bonding (UATLP) was used to rapidly join dissimilar Al/Mg alloys in the air. The pure Zn interlayer was chosen to prevent Al–Mg intermetallic compounds (IMCs). The effects of the bonding time on the microstructure and mechanical properties of the joints were studied. The joint formation mechanism was analyzed. Results show that the Al–Mg IMCs can be avoided when the ultrasonic time was shorter than 3 s. The oxide layer on the Al substrate was incompletely removed when the ultrasonic time was shorter than 2 s, and the joint was characterized by Mg–Zn eutectic, MgZn, and MgZn2 from the Mg side to the Al side. The joint had a shear strength of 16 MPa and failed through the MgZn2/Al interface under such condition. The oxide layer on the Al substrate was removed when the ultrasonic time was increased to 3 s. The joint had a shear strength of 24 MPa, and it failed through the MgZn2 layer and the Mg–Zn eutectic. The entire Zn foil interacted with the Mg and Al substrate at a prolonged ultrasonic time of 6 s. Al–Mg IMCs of Al3Mg2 and Al12Mg17 appeared because a large amount of Al and Mg atoms diffused into the joint. The joint strength decreased to 11 MPa and failed through the Al3Mg2 layer.

Current Research Developments of Electromagnetic Joining Technology in China-A Review

: With the increasing applications of multi-material structures in lightweight vehicle, traditional joining techniques are highly challenged in joining dissimilar materials. To meet the multimaterial structures requirements of lightweight design, electromagnetic joining (EMJ) technology, including electromagnetic riveting (EMR) and magnetic pulse welding (MPW), developed rapidly in recent years, which can achieve good connection performance for complex-shaped structures and dissimilar materials. This paper presents a comprehensive review of the research progress of the EMJ technology in China. Moreover, this review aims at providing a guideline for researchers engaged in electromagnetic joining technology and other connecting processes to further improve the level of lightweight vehicle design and manufacture. Firstly, the development history and status of EMJ were presented. Then the basic joining principles and characteristics of EMR and MPW were analyzed in detail. Subsequently, the investigation of joints formation mechanism, mechanical properties of joints and equipment development of EMR and MPW techniques were reviewed and analyzed. Specially, the operating principle is described along with various factors affecting the mechanical and microcosmic properties of joints. Finally, the future development trend of the EMJ technology based on the current research progress is highlighted.

Joining by forming technologies: current solutions and future trends

The progressively more demanding needs of emissions and costs reduction in the transportation industry are pushing engineers towards the use of increasingly lightweight structures. This goal can be achieved only if dissimilar and/or new materials, including polymers and composites, are joined together to create complex structures. Conventional fusion welding processes have often been proven inadequate to this task because of the high heat input reducing the joint mechanical properties or even making the joining process impossible. Joining by forming technologies take advantage on the plastic deformation to create sound joints out of even very dissimilar materials. Over the last 25 years, several new processes, with increasing potential in effectively joining virtually every structural material, have been invented and developed. In the paper, a comprehensive overview of the most utilized joining by forming processes is given. For each process, an analysis of the current research trends and hot topics is provided, highlighting strengths and weaknesses for industrial applications.

Effects of ageing frequency on the interfacial failure and tensile properties of adhesively bonded Arcan joints exposed to cyclic ageing environments

The strength and durability of adhesive joints are significantly influenced by environmental conditions. When working in a humid environment, the adhesive tends to absorb moisture and this phenomenon can drastically reduce the mechanical performance of the adhesive joints. In practise, joints are usually subjected to cyclic ageing due to moisture absorption and desorption. Accordingly, it is necessary to study the ageing behaviour of the adhesives when they are exposed to environments with cyclic humidity conditions. Accordingly, the current study investigates the mechanical properties of adhesive joints with an epoxy-based adhesive subjected to cyclic ageing conditions using Arcan joint specimens. To this aim, static tensile tests were performed for both cyclic aged, dried, and unaged Arcan joints. The effect of cyclic ageing and drying conditions, such as absorption and desorption mechanisms, on the mechanical properties of the joints were studied. In the numerical part, an experimentally obtained diffusion coefficient (D) was used to simulate the water diffusion in Arcan joint. The results showed that key mechanical properties, such as tensile strength and displacement of the joints are reduced by the number of ageing cycles. The maximum strength degradation of the aged joints compared to the unaged condition was 94% for the third ageing cycle. For the dried condition, the strength of the joints was recovered although it was not fully returned to the initial stage. It was also found that the recovery ratio increases with the ageing cycles. It is shown that a short drying process can significantly recover the mechanical response of the cyclically aged adhesive joints, especially at higher ageing cycles.

Experimental investigation of high impact polystyrene/metal self‐piercing riveted joint

AbstractSelf‐piercing riveting was adopted to join high impact polystyrene (HIPS) and metal sheets which had huge difference in material properties. Three kinds of metal sheet (AA1060, AA5052, and HC340LA) were joined to HIPS sheet. The effect of polymer sheet thickness on mechanical properties of joints was investigated. The static loads of joints were measured in tensile and shearing tests. The failure modes of joints were analyzed. The cross sections of joints were observed by metallographic microscope. Results showed that self‐piercing riveting could effectively join HIPS and metal sheets when polymer sheet was placed as top sheet. All joints failed in the manner of polymer fracture in both tensile and shearing tests. For joints with different sheet material combinations, though the cross sections and geometrical parameters of joints had great difference, the static loads and absorbed energy values of joints were nearly the same. When AA5052 sheets were joined to HIPS sheets with different thickness values, with the increase of polymer sheet thickness, the flaring degree of rivet decreased, while static loads and absorbed energy values of joints increased. This was because the strength of interlock structure was higher than that of polymer sheet and the strength of joint was determined by the strength of polymer sheet.

Effect of process temperatures on material flow and weld quality in the friction stir welding of high density polyethylene

The material flow in the weld zone of friction stir welded bi-modal high density polyethylene (HDPE) was investigated under different in-process temperatures. The in-process temperatures were controlled by changing the tool rotation speed, welding speed and the material initial temperature. Boundary temperature measurements were recorded on the top and bottom surfaces of the welded plates and the temperature distribution in the workpiece was determined numerically using an iterative inverse heat conduction method. Material flow patterns were observed by welding two different colors of the polymer blanks, white on the advancing side and black on the retreating side. Joint quality was assessed using optical microscopy, and joint strength and elongation were measured by tensile testing. It was found that process temperatures greatly affect the extent of material flow in the weld zone, which in turn affects the tendency to form defects and the overall joint mechanical properties. It was also found that proper fusion across the interfaces occurs when the material in the welding zone was maintained at temperatures in excess of 100 °C across the thickness. The high temperature conditions instigated proper fusion of the material, which in turn resulted in large weld efficiencies and elongations in excess of 100%.

Analysis and control of axial pressure in high-speed friction stir welding of alloy sheet

Aiming at the high-speed friction stir welding deformation and thickness reduction of 1 mm 6061-T6 aluminum alloy sheet, the characteristics of the axial pressure of the welding process and its influence on the joint structure and mechanical properties were analyzed in this paper. Experiments were performed to optimize process parameters. A fuzzy controller with axial pressure error and its change rate as input and welding speed as output had been designed to realize axial pressure control during friction stir welding. The welding axial pressure fluctuates slightly around the target value, and the system was stable with the controller. Besides, the microstructure of the corresponding weld nugget area was uniform, dense, and the transition area was uniform without obvious welding defects. The joint hardness distribution was stable with the classic “W” shape distribution. The mechanical properties of the joint were excellent, and the tensile strength reaches 195 MPa, which was about 70% of the base material (290 MPa).

Electron beam offset welding to ameliorate metallurgical compatibility and mechanical performance of refractory metal/Ni-base superalloy dissimilar alloys: Nb/GH3128

Electron beam welding of Nb/GH3128 dissimilar alloys was conducted to obtain crack-free joints. The beam offset process contributed to the improvement of microstructure, and segregation behavior of alloying elements, as well as the elevation of mechanical properties of joints. Cracked joints were obtained as electron beam shift to GH3128 superalloy with 0.5 mm. Brittle Ni6Nb7/Laves reaction layer combined with a great number of brittle Laves phase and γ/Laves eutectic in fusion zone acted as the intrinsic factors for cracking. Relative low segregation propensity of alloying elements helped to the promotion of generation of γ/Laves eutectic. As the beam offset value increased from 0.5 mm to 0.9 mm, the tendency of alloying elements to segregate was intensified, promoting the Laves phase and γ/Laves eutectic to be replaced by γ phase, and the hardness of the joints was gradually decreased from 594 HV to 340 HV correspondingly. High hardness is detected in the reaction layer between Nb and the fusion zone, which triggered the brittle fracture of all joints. The joint obtained with a beam offset value of 0.8 mm possess the highest tensile strength 163 MPa, 65% of Nb base metal.

Study on microstructure and mechanical behavior relationship for laser-welded dissimilar joint of P92 martensitic and 304L austenitic steel

A dissimilar laser beam welded joint of ferritic/martensitic P92 steel, and 304L austenitic stainless steel (ASS) has been examined in as-weld and post-weld heat treatment (PWHT) at 760 °C for 120 min for microstructure feature and mechanical aspects. The microstructure of the weld metal, interface, and heat-affected zone (HAZ) was characterized in detail, and it was observed that a great level of inhomogeneity exists in a dissimilar joint. In addition, the effect of the inhomogeneity in microstructure on mechanical properties, microhardness, and impact strength of the welded joint was discussed. The welded joint's mechanical properties met the USC boiler requirement for both as-weld and PWHT situations. The welded joint showed a decent combination of tensile strength and impact strength for both as-weld and PWHT conditions. The tensile results showed the failure from the 304L SS base metal, which ensured the acceptable strength of the weld metal for the laser welded joints. The part of the welded joint with relatively poor impact strength was the weld metal. Though, the Charpy impact toughness of the weld metal (89 J) was measured higher than the ASME standard value (>41 J) and EN 1599:1997 standard value (>47 J) in the as-weld situation. The impact strength of the weld fusion zone was 138 J in PWHT condition.

Microstructural Characterization and Mechanical Properties of AA5083 Aluminum to AISI 1018 Steel Welds by Electro Spark Microwelding

ABSTRACT Welding of aluminium alloys to steels has been always challengeable. There are a certain number of methods to join these dissimilar metals all have their advantages and disadvantages. Advancement of any aluminium to steel welding strategies is an approach to control the size and nature of the intermetallic compound layer. A new method of electro spark microwelding has been developed for dissimilar welding of an aluminium alloy to steel to improve the joint mechanical properties. The microstructure of the welds are investigated by scanning transmission electron microscopy. The maximum tensile strength reached 206 MPa representing 65% of the tensile strength of the parent aluminium alloy with a ductile fracture locating at the fusion zone. The excellent bonding of the aluminium alloy and steel was based on the combined effects of the formation of about 4 μm thick nanoscale Fe rich intermetallic compound layer and complex mechanical inter-locking. The current research confirmed that aluminium could be successfully welded to steel via electro spark microwelding process.

The Influence of Friction Time on the Joint Interface and Mechanical Properties in Dissimilar Friction Welds

The welding of dissimilar materials is one of the challenging issues in thefabrication industry to obtain required quality welds using fusion weldingmethods. However, some processes recently improved interface bondingwith low joint strength. Unfortunately, the major intermetallic compoundscould not alleviate from the joint interface. Alternatively, solid-statewelding methods revealed fewer intermetallics at the joint interface fordissimilar material welds. Among them, friction welding was chosen to joinincompatible materials with the necessary properties successfully. Frictiontime is a critical parameter for obtaining strong welds through frictionwelding, apart from friction pressure, forging pressure, forging time, androtational speed. Variability of friction time can change the strength offriction by changing mechanical properties such as tensile strength. Thischange of tensile strength is typically influenced by the intermixing region,dependent on friction time. In this experiment, carbon steel and stainlesssteel have been friction welded to test the impact of friction time on thejoint interface where the substrate’s faying surface meets. This interfaceconsists of the intermixing region of the two materials on which the frictionwelding is performed. The results showed an interesting variation in tensilestrength, with varying friction time. The width of the intermixing zoneincreased gradually with friction time until and decreased with the furtherincreasing. The strength of the welds obtained was the highest of 730 MPaat a friction time of 4 s and fell as friction time’s increased value after 4 s.

Improvement for Ti3SiC2/Cu joint brazed using composite fillers with abnormal expansion ceramic particulates

AbstractReducing the residual stresses and improving the mechanical strength of large‐scale ceramic/metal brazing joints is an important problem that must be solved for its practical engineering application. Using composite filler with solid‐state phase transformation ceramic particulates, it is theoretically feasible to relieve the residual stress and improve the mechanical properties of ceramic/metal brazed joints. In this study, Cu mesh, Ag–28Cu–2Ti (wt.%), and yttria‐stabilized zirconia (0.6 mol.% YSZ solid‐state phase transformation ceramic particulates) composite power fillers were used in the brazing of Ti3SiC2 ceramic and pure copper. The microstructure of joints and YSZ particulates in the interface was investigated and confirmed by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). In addition, the effect of YSZ particulates content on the mechanical properties of joints was investigated and evaluated by the shear strength. The results show that the interfacial phases were mainly Ti5Si3, TiC, TixCu, Ag (s, s), Cu (s, s), and YSZ particulates. Moreover, most of YSZ particulates undergo the solid‐state phase transformation from tetragonal zirconia (t‐ZrO2) to monoclinic zirconia (m‐ZrO2) during the cooling process of brazing. The abnormal volume expansion of the solid‐state phase transformation reduced the thermal mismatch between Ti3SiC2 ceramic and filler, thereby reducing the residual stress in the interface of joint. When using composite filler with 6 wt.% YSZ particulates, the shear strength of Ti3SiC2/Cu joint reached the maximum. The maximum average shear strength of the joints was 80.2 MPa, which was about 103.6% more than the joint without YSZ particulates.

Bolt insertion damage and mechanical behaviors investigation of CFRP/CFRP interference fit bolted joints

Interference fit has advantages in improving fatigue behaviors of composite bolted joints; however, interference fit bolt insertion tends to cause damages in laminates weakening joint mechanical properties. Therefore, an experimental study was conducted to investigate bolt insertion damages of Carbon Fiber Reinforced Polymer (CFRP)/CFRP interference fit bolted joints. Mechanical behaviors of joints were also evaluated experimentally under both quasi-static loads and cyclic loads. Scanning Electron Microscope (SEM) and high-resolution X-ray micro-CT scan were used to examine micro damages in laminates. Damage and failure behaviors of joints were characterized. The results demonstrated that the hole entrance in upper laminate and the laminate boundary near the hole wall were the most critical regions for damages during bolt insertions. However, the influence of those damages on quasi-static failure loads and fatigue failure modes of joints was minimal. Delamination and matrix cracking occurred first in laminates following fiber and matrix fracture in quasi-static tensile tests. Interference fit could improve the fatigue resistance of the laminate hole; however, the bolt seemed to suffer a more critical local fatigue loading condition. This paper can contribute to composite structure designs, especially in understanding damage and failure behaviors of composite bolted joints.

Effect of S-curve laser power for power distribution control on laser oscillating welding of 5A06 aluminum alloy

Laser oscillating welding of 5A06 aluminum alloy is widely used in industry. In order to improve the performance of Al-based welded joints and reduce welding defects, this paper details the effects of employing an S-curve laser power which is distributed along the laser oscillating path (sine wave) to improve the microstructure and mechanical properties of the joints. By applying the S-curve and an equal power condition to the 5A06 aluminum alloy, bottom butt sinusoidal path laser oscillating welding was performed. The welding appearance, microstructure and mechanical properties of the welded joints under two laser oscillating welding processes were investigated. Our results showed that laser oscillating welding using the S-curve power allows to obtain good joints when compared to the joints produced with constant power. When the linearly varying laser power of “high-low-high” applied periodically was employed, the grains in the joint structure showed the cyclic “growth-inhibition-growth” phenomenon. This growth mechanism not only refined the grain structure, but also narrowed the columnar region, and improved the mechanical properties of the joint. Compared with the laser oscillating process with constant power, the tensile strength of the joints using the S-curve power was increased by 35.3 %. Moreover, the tensile strength of the welded test coupons with S-curve power was 337 MPa, which is about 99.1% of the base metal (340 MPa). The welded joints using the S-curve power showed larger and deeper dimples, highlighting higher ductility and good plasticity. This paper provides a new approach for the research of laser oscillating welding and the control of laser power to improve the mechanical properties of welded joints.

Stationary shoulder friction stir welding of Al–Cu dissimilar materials and its mechanism for improving the microstructures and mechanical properties of joint

The fundamental reasons for the poor mechanical properties of the Al–Cu conventional friction stir welding (CFSW) joints are serious material mixing and excessively thick intermetallic compounds (IMCs). In this study, stationary shoulder friction stir welding (SSFSW) was innovatively applied to join the Al–Cu dissimilar materials. The results indicated that the material mixing and the IMCs growth were successfully suppressed. Compared with the CFSW, the grains in the SZ of the SSFSW joint were refined and the plastic deformation in the SZ was enhanced. This was attributed to the frictional driving force of SSFSW was higher than that of CFSW. The mutual diffusion reaction of Al and Cu elements was inhibited owing to the lower heat input of the SSFSW. The mechanical properties of the joints were significantly improved by the SSFSW. The tensile strength of the optimal SSFSW joint was found to be 211.4 MPa which is 15.1% higher than that of the optimal CFSW joint. Moreover, the fracture occurred in the Al matrix. Reducing the stress concentration in the SZ caused by materials mixing was shown to be the main mechanism for SSFSW to improve the tensile performance of the joint.

Microstructural evolution and mechanical properties of the Al–Cu dissimilar joint enhanced by stationary-dynamic shoulder friction stir welding

Material mixing and intermetallic compounds (IMCs) are the key factors that affect the mechanical properties of dissimilar metal joints. In this paper, a feasible method of stationary-dynamic shoulder friction stir welding has been developed, which reduces the mixing of materials and inhibit the growth of IMCs during the Al-Cu welding process. The stationary-dynamic shoulder was composed of a stationary shoulder with a larger diameter and a rotational shoulder with a smaller diameter. While the stationary shoulder provided the upsetting force to guarantee the weld formation, the rotational shoulder served for material stirring and heat input. Compared with conventional friction stir welding, the mechanical properties of joints obtained by the new method were significantly improved. The maximum tensile strength was 243 MPa, which was equivalent to 90 % of Cu base metal and 54 % of Al base metal. Furthermore, the evolution of IMCs across the transition layer was analyzed in depth. The results indicated that, with an increase in the rotation speed, the IMCs layer gradually became thicker. However, when the thickness reached a certain level, it promoted the generation of micro-cracks on IMCs and reduced the strength of the joint. According to thermodynamic and kinetic analysis, IMCs were formed with respect to Al2Cu-Al4Cu9 sequence, which was consistent with transmission electron microscopy results.

Role of ultrasonic in synergistic strengthening of friction stir welded alloys by grain refinement and rapid nanoscale precipitation

The trade-off between welding and strength loss of metal materials has been a troublesome question for decades. Improving joint efficiency is of considerable importance for industries. In the present study, grain refinement and rapid nanoscale precipitation in Al–Li alloys welds are concurrently achieved by ultrasonic enhanced friction stir welding (UFSW), improving the mechanical properties of joints. The results indicated that microstructures in the stir zone (SZ) were refined by the ultrasonic due to the enhanced dynamic recrystallization (DRX). Moreover, prominent nanoscale precipitation was observed in the SZ during UFSW. Under the effect of the ultrasonic, T1 (Al2CuLi) phases can precipitate through heterogeneous nucleation mechanism on a pre-existing θ′ (Al2Cu) phase, instead of starting from a supersaturated solid solution as that in traditional heat treatments. Therefore, both the precipitation velocity and nucleation rate were accelerated in UFSW. Based on the experimental discovery of orientation relationships between the T1 and θ′ phases (0001)T1//(312)θ′ and (2-1-10)T1//(-112)θ′, a theoretical model for T1 precipitation via heterogeneous nucleation was established, which coincided well with the observation by selected area electron diffraction. Excess vacancies introduced by the ultrasonic contributed to the enhanced DRX and nanoscale precipitation via the heterogeneous nucleation mechanism.