Joint Formation Mechanism Research Articles

Joint Formation Mechanism of Rotary Friction Welding Characterized by Seaming Ratio

Joint Formation Mechanism of Rotary Friction Welding Characterized by Seaming Ratio

Laser-induced exothermic bonding of carbon fiber/Al composites and TiAl alloys

In this paper, a highly-efficient method for bonding Carbon Fiber (Cf)/Al composites and TiAl alloys was developed by means of laser-induced exothermic reaction of a Ni-Al-Ti interlayer. To examine the interlayer exothermic performance, the adiabatic temperature was calculated and the reaction temperatures were measured. Based on SEM, XRD and TEM, the interfacial reactions between carbon fiber and interlayer products were investigated. Results show that the addition of Ti enhanced the interfacial reactions between carbon fibers and interlayer products. The resulting formation of a 300–400nm thin Ti-C layer at the NiAl3/carbon fiber interface was identified as a key player in improving the joining quality on the Cf/Al side. The typical interfacial structure of the joint is (Cf/Al)/Ti-C/NiAl3/Ni2Al3/(NiAl+Al3NiTi2)/Al3NiTi2/TiAl. The joint formation mechanism was discussed. In addition, the effect of Ti content on the microstructure and mechanical properties of joints were investigated in detail. The optimum value of Ti content was found to be 5wt.%, leading to a defect-free joint and a maximum shear strength of 45.8MPa.

Adhesion of Steel and PMMA by Means of Laser Radiation

As the utilization of plastics is growing in our devices, their joining with other structural materials, like metals is more and more necessary. A novel method for joining polymeric materials and metals is the laser assisted metal plastic joining. The method is in focus of several researches. However, the mechanism of joint formation is not described sufficiently yet. In this study, the adhesion between structural steel and PMMA plastic and the phenomena of bubble formation is investigated. Scanning electron microscopy (SEM), thermogravimetry and mass spectrometry (TG-MS) were used to analyze joining interfaces and changes in the plastic material. Results show good adhesion between the mentioned materials and the important role of bubbles in the evolution of joining force.

Ultrasonic-promoted rapid TLP bonding of fine-grained 7034 high strength aluminum alloys

High strength aluminum alloys are extremely sensitive to the thermal cycle of welding. An ultrasonic-promoted rapid TLP bonding with an interlayer of pure Zn was developed to join fine-grained 7034 aluminum alloys at the temperature of lower 400°C. The oxide film could be successfully removed with the ultrasonic vibration, and the Al-Zn eutectic liquid phase generated once Al and Zn contacted with each other. Longer ultrasonic time can promote the diffusion of Zn into the base metal, which would shorten the holding time to complete isothermal solidification. The joints with the full solid solution of α-Al can be realized with the ultrasonic action time of 60s and holding time of only 3min at 400°C, and the shear strength of joints could reach 223MPa. The joint formation mechanism and effects of ultrasounds were discussed in details.

Microstructure and Mechanical Properties of Overcast 6101–6101 Wrought Al Alloy Joint by Squeeze Casting

The wrought Al alloy–wrought Al alloy overcast joint was fabricated by casting liquid 6101 Al alloy onto 6101 Al extrusion bars and solidifying under applied pressure. The joint interfacial microstructure was investigated; the effect of applied pressure on the microstructure and mechanical properties was evaluated. The mechanism of joint formation and mechanical behaviors of both squeeze cast 6101 and 6101–6101 overcast joint material were analyzed. The results show that with the application of pressure during solidification process, wrought Al alloy 6101 could be cast directly into shape successfully. Excellent metallurgical bonding was then formed in the overcast joint by electro-plating 6101 solid insert with a layer of zinc coating, and a transition zone formed in the joint region. During the tensile test, the fracture occurs in the 6101 solid insert part with the ultimate tensile strength (UTS) of 200 MPa, indicating that the strength of the overcast joint is higher than 200 MPa, and the tensile strength of overcast joint material is independent on the magnitude of applied pressure. For Al–Al overcast joint material, if a clean and high strength joint is formed, the UTS and yield strength (YS) are determined by the material with the lower value, while for EL, the value is determined by the length proportion and the stress–strain behavior of both components.

Strength and Phase Identification of Autogenous Laser Brazed Dissimilar Metal Microjoints

The continued advancement of implantable medical devices has resulted in the need to join a variety of dissimilar, biocompatible metal pairs to enable selective use of their unique properties. Typical materials used in implantable medical devices include stainless steel (SS), titanium, platinum (Pt), as well as shape memory materials such as NiTi. Joining these dissimilar metal pairs, however, often results in excessive formation of brittle intermetallics, which significantly reduce the strength of the joints. The use of filler materials to combat the formation of intermetallics, however, results in reduced biocompatibility. Autogenous laser brazing is a novel process that is able to form thin, localized joints between dissimilar metal pairs without filler materials. In this study, the formation of autogenous laser brazed joints between NiTi and SS wires is investigated through experiments and numerical simulations. The strength, composition, microstructure, and phase formation of the resultant joints are investigated as a function of processing parameters and thermal, fluid flow, and phase prediction simulations are used to aid in understanding the joint formation mechanism.

Joining of dissimilar materials

Emerging trends in manufacturing such as light weighting, increased performance and functionality increases the use of multi-material, hybrid structures and thus the need for joining of dissimilar materials. The properties of the different materials are jointly utilised to achieve product performance. The joining processes can, on the other hand be challenging due to the same different properties. This paper reviews and summarizes state of the art research in joining dissimilar materials. Current and emerging joining technologies are reviewed according to the mechanisms of joint formation, i.e.; mechanical, chemical, thermal, or hybrid processes. Methods for process selection are described and future challenges for research on joining dissimilar materials are summarized.

Local Phenomena During Riveting Process

Abstract The paper presents experimental and numerical study of the local phenomena during the riveting process. It is commonly accepted that technological factors of the riveting process has a strong influence on the fatigue life of riveted joints. The authors analysed the papers concerned the experimental researches of the riveting force influence on fatigue life. The magnitude of the life increase caused by the riveting force increase suggests the authors that this is not only the result of beneficial stress system but the change of the joint formation mechanism has taken place. This was an inspiration to undertake more detailed researches of the riveting process. The strain progress during the riveting process has been experimentally investigated for four types of aluminium rivets used in airframes. Measurements confirm very high strains near the driven head. For some types of rivets the reversal strain signal has been recorded. Several FE model has been use to investigate the riveting process. The axisymmetric and solid models were used. The agreement of experimental and numerical results in some cases were good, in other cases the numerical models demand further development. In any calculations, the reversal strain effect has not been obtained, This suggest that it is result of the phenomenon which has not been taken into account in numerical modelling. The working hypothesis has been assumed that during the riveting process adhesive joints (called cold welding) were formed and destroyed during the process, what was the reason of the observed reversal strain signal. The authors are going to continue this investigation.

Effect of Interlayer Thickness on Joint Formation Between Ti-6Al-4V and Mg-AZ31 Alloys

The joining of a Ti-6Al-4V alloy to a Mg-AZ31 alloy was performed using Ni electroplated coatings during the TLP bonding process. In this work, different coating thicknesses were used ranging from 1 to 20 μm. The effect of the coat thickness on microstructural developments and mechanical properties was studied. The bonded specimens were examined by metallographic examination, scanning electron microscopy, and X-ray diffraction analysis. It was observed that as the coat thickness increased from 1 to 12 μm, the joint shear strength increased from 9 to 47 MPa. A further increase in coat thickness had a detrimental effect on the bond strength, and a lower value of 11 MPa was recorded. The mechanism of joint formation includes three stages: solid-state diffusion, eutectic formation, and isothermal solidification.

Joining Processes by Plastic Deformation

As the scale and complexity of products such as aircraft and cars increase, demand for new functional processes to join mechanical parts grows. The use of plastic deformation for joining parts potentially offers improved accuracy, reliability and environmental safety as well as creating opportunities to design new products through joining dissimilar materials. This paper aims to provide an overview of the state of the art in such joining processes, including cold welding, friction stir welding, joining by forming, self-pierce riveting and mechanical clinching. The paper includes description of the mechanism of joint formation, joint strength and applicability.

Transient liquid phase (TLP) brazing of Mg–AZ31 and Ti–6Al–4V using Ni and Cu sandwich foils

Transient liquid phase (TLP) brazing of Mg–AZ31 alloy and Ti–6Al–4V alloy was performed using double Ni and Cu sandwich foils. Two configurations were tested; first, Mg–AZ31/Cu–Ni/Ti–6Al–4V and second, Mg–AZ31/Ni–Cu/Ti–6Al–4V. The effect of set-up configuration of the foils on microstructural developments, mechanical properties and mechanism of joint formation was examined. The results showed that different reaction layers formed inside the joint region depending on the configuration chosen. The formation of ϵ phase (Mg), ρ (CuMg2), δ (Mg2Ni) and Mg3AlNi2 was observed in both configurations. Maximum shear strength obtained was 57 MPa for Mg–AZ31/Ni–Cu/Ti–6Al–4V configuration and in both configurations, the increase in bonding time resulted in a decrease in joint strength to 13 MPa. The mechanism of joint formation includes three stages; solid state diffusion, dissolution and widening of the joint, and isothermal solidification.

Research of Fluxless Soldering of High-Purity Aluminium with Solders Type Zn-Al

The aim of work consists in the study of interactions on solder/substrate boundary in fluxless soldering of Al with 4N purity by ultrasound activation. The ZnAg6Al6 and ZnAl4 solders were used in experiments. The soldering parameters were as follows: soldering temperature from 400 oC to 420 oC, acting time of ultrasonic vibrations 5 to 20 s, ultrasound frequency 40 kHz. Soldered joints were assessed by optical light microscopy, EDXmicroanalysis and XRD analysis. It was found out that the ZnAg6Al6 solder is composed of αAl, βZn solid solutions and AgZn3phase. The ZnAl4solder consists of βZn primary solid solution and a lamellar eutectic Zn-Al structure. The main mechanism of joint formation between the solders type Zn-Al and Al substrate during soldering consists in eutectic reaction between the liquid Zn and solid Al. An eutectic βZn-αAl mixture was observed on the joint boundary in case of both solders. In case of Al/ZnAg6Al6 joint also AgZn3intermetallic compound was observed in the transition zone.

Diffusion Vacuum Brazing of TiAl48Cr2Nb2 Casting Alloys Based on TiAl (<i>γ</i>) Intermetallic Compound Using Ag-Cu-Ti Braze Alloy

Fast-developing such advanced industries as aviation, automotive and power-generation are increasing demand for new engineering materials which could resists such extreme operation conditions as high operating temperature, considerable stresses or operation in fume-affected environment. Highly desirable properties of such materials should include high hardness and strength, corrosion resistance (also when exposed to aggressive fumes) but also, first of all, low density. However such materials also requirements engineering methods to ensure obtain of good sound joints. Results in growing interest in modern engineering materials characterised by increasingly better operational parameters combined with a necessity to obtain joints of such materials representing good operation properties create important research and technological problems of today. These issues include also titanium joints or joints of titanium alloys based on intermetallic compounds. Brazing is one of the basic and sometimes even the only available welding method used for joining the aforesaid materials in production of various systems, heat exchangers and, in case of titanium alloys based on intermetallic compounds, turbine elements and space shuttle plating etc. This article presents the basic physical and chemical properties as well as the brazability of alloys based on intermetallic compounds. The work also describes the principle and mechanisms of diffusion-brazed joint formation as well as reveals the results of metallographic and strength tests involving diffusion-welded joints of TiAl48Cr2Nb2 casting alloy based on TiAl (γ) phase with the use of sandwich-type layers of silver-copper-titanium based filler metal (Ag-63%; Cu-35,5%; Ti-2%). Structural examination was performed by means of light microscopy. Furthermore, the article reveals the results of shear strength tests involving the aforementioned joints. Obtained mechanical test results of TiAl48Cr2Nb2 joints brazed with usage of three/different filler metal alloys ware compared.

In Situ Measurement of the Thermal Contact Resistance of an Al Lap Joint During Braze Processing

A technique was developed, using a laser flash thermal diffusivity apparatus, to measure the thermal contact resistance, Rc, of an Al lap joint during braze processing. The method required a determination of the temperature dependence of the thermal diffusivity of the individual Al braze sheets, as well as a two-layer lap joint made from these sheets, under identical conditions. A two-layer modeling method was then used to analyze the above data to determine Rc for the lap joint as a function of processing temperature. This in situ analysis of Rc for a developing joint during brazing was able to distinguish both solid-state and liquid-phase reactions occurring at the faying surfaces of the joint. Consequently, it represents a powerful, new experimental tool that can be used to investigate the mechanisms of braze joint formation and the thermal properties of a joint as a function of processing condition. In the particular case of this study, the technique demonstrates that the use of a Ni-based fluxless brazing process to join aluminum (Al) sheets, reduced the Rc of the lap joint by 100-folds from 1.3 × 10−4 m2 K/W before brazing to 1.35 × 10−6 m2 K/W after brazing.

Mechanisms of joint formation throughout semisolid stir welding of AZ91 magnesium alloy

Joining in the semisolid state is considered a possible method to join alloys to each other. The mechanisms taking part in semisolid stir welding of AZ91 alloys were investigated. Two 7.5 mm-thick AZ91 pieces and a 2 mm-thick Mg-25%Zn interlayer piece were placed in a heating plate. After holding for 3 min at a desired temperature, the weld seam was stirred by a rotational tool. The heating plate was travelled on a trolley at a constant speed of 4.6 cm/min. In addition, one sample was welded without interlayer. Evolution of welding as a function of stirring rate, tool shape and temperature was studied throughout this welding process with scanning electron and optical microscopes. Interlayer decreases the joining temperature and assists to investigate the possible semisolid stir welding mechanisms. Increasing temperature and stirring rate, and using round stirrer instead of grooved stirrer increase the stir zone width. The results show that some possible mechanisms are helpful to achieve a proper metallurgical bonding in the welding process, such as oxide layer disruption, liquid phase blending, globule joining, and liquid penetration to the base metal, merging a group of globule into stir zone from the base metal.

Characteristics and properties of Bi‐11Ag solder

PurposeThe purpose of this paper is to study Bi‐11Ag solder for higher application temperatures. The aim of the research work was to determine the soldering, thermal and mechanical properties of Bi‐11Ag solder.Design/methodology/approachTo determine the melting point interval of experimental Bi‐11Ag solder, DSC analysis was performed. The contact angles were studied on a copper, nickel and silver substrate by use of a sessile drop method. Wettability tests were realised at a temperature of 380°C in a shielding atmosphere (90% N2+10% H2). Based on experience achieved with wetting angle measurements, the specimens for measurement of shear strength of Cu, Ni and Ag/Bi‐11Ag joints were fabricated. EDX analysis was used for the study of the solder interaction with the surface of the three metallic substrates.FindingsThe best wettability at soldering in a shielding atmosphere was achieved with silver. The wetting angle at 30 min attained the value of 23°. The worst wettability was observed on copper, where at 30 min the wetting angle was 55°. Average shear strength varied from 31 to 45 MPa. The highest strength was obtained with the Cu substrate whereas the lowest was with the Ni substrate. The lowest strength achieved with the Ni substrate was caused by formation of brittle intermetallic phase NiBi3. Joint formation is realised by eutectic reaction at the contact of Bi with the surface of the copper substrate. Similar joint formation by eutectic reaction occurs also at Bi interaction with the surface of the Ag substrate. At Bi interaction with the nickel substrate a new intermetallic phase (NiBi3) is formed.Originality/valueWettability of Bi‐11Ag solder on Cu, Ag and Ni substrates was determined at application of a shielding atmosphere (90% N2+10% H2). Wettability was determined also at application of ZnCl2‐NH4Cl flux. The shear strength of Bi‐11Ag on different substrates was determined. The mechanism of joint formation was analysed.

Joining by plastic deformation

As the scale and complexity of products such as aircraft and cars increase, demand for new functional processes to join mechanical parts grows. The use of plastic deformation for joining parts potentially offers improved accuracy, reliability and environmental safety as well as creating opportunities to design new products through joining dissimilar materials. This paper aims to provide an overview of the state of the art in such joining processes, including cold welding, friction stir welding, self-pierce riveting, mechanical clinching and joining by forming. The paper includes description of the mechanism of joint formation, and analysis of joint performance and applicability.

Regeneration of Limb Joints in the Axolotl (Ambystoma mexicanum)

In spite of numerous investigations of regenerating salamander limbs, little attention has been paid to the details of how joints are reformed. An understanding of the process and mechanisms of joint regeneration in this model system for tetrapod limb regeneration would provide insights into developing novel therapies for inducing joint regeneration in humans. To this end, we have used the axolotl (Mexican Salamander) model of limb regeneration to describe the morphology and the expression patterns of marker genes during joint regeneration in response to limb amputation. These data are consistent with the hypothesis that the mechanisms of joint formation whether it be development or regeneration are conserved. We also have determined that defects in the epiphyseal region of both forelimbs and hind limbs in the axolotl are regenerated only when the defect is small. As is the case with defects in the diaphysis, there is a critical size above which the endogenous regenerative response is not sufficient to regenerate the joint. This non-regenerative response in an animal that has the ability to regenerate perfectly provides the opportunity to screen for the signaling pathways to induce regeneration of articular cartilage and joints.

Crossed-Wire Laser Microwelding of Pt-10 Pct Ir to 316 Low-Carbon Vacuum Melted Stainless Steel: Part I. Mechanism of Joint Formation

The excellent biocompatibility and corrosion properties of Pt alloys and 316 low-carbon vacuum melted (LVM) stainless steel (SS) make them attractive for biomedical applications. With the increasing complexity of medical devices and in order to lower costs, the challenge of joining dissimilar materials arises. In this study, laser microwelding (LMW) of crossed Pt-10 pct Ir to 316 LVM SS wires was performed and the weldability of these materials was determined. The joint geometry, joining mechanism, joint breaking force (JBF), and fracture modes were investigated using optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and microtensile testing. It was shown that the mechanisms of joint formation transitioned from (1) brazing, (2) a combination of brazing and fusion welding, and (3) fusion welding with increasing pulsed laser energy. The joints demonstrated various tensile failure modes including (1) interfacial failure below a peak power of 0.24 kW, (2) partial interfacial failure that propagated into the Pt-Ir wire, (3) failure in the Pt-Ir wire, and (4) failure in the SS wire due to porosity and severe undercutting caused by overwelding. During this study, the optimal laser peak power range was identified to produce joints with good joint geometry and 90 pct of the tensile strength of the Pt-10 pct Ir wire.

Resistance Microwelding of Au/Ni-Plated Phosphor Bronze Sheet to Insulated Cu Wire

Resistance microwelding of Au/Ni-plated phosphor bronze sheet to insulated Cu wire have been investigated using mechanical testing, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that mechanisms of joint formation involve solid-state bonding with Au and Cu atoms diffusion at low welding current, a combination of brazing and solid-state bonding at high welding current. Due to the hindrance of Ni plating which has a higher melting temperature and hardness, the joint breaking force is smaller than that without plating.