Z. B. Dong

Harbin Institute of Technology | HIT · School of Materials Science and Engineering

TiAl alloy is sensitive to welding cracks and exhibits brittle nature at room temperatures. The formation of the α2-Ti3Al phase coupled with high welding residual stress has been proved to be the key factor triggering the cracking of the joint. To improve the microstructure of the weld, a zipper shape joint is designed to decrease the cooling rate...

A favorable microstructure is a perquisite for ensuring the quality of welding joints, but grain coarsing inevitably occurs in the heat‐affected zone (HAZ). Controlling the reduction of deterioration as much as possible is a key problem in welding engineering. Based on the welding experiment, a finite element model considering the contact heat tran...

In view of the excellent soft magnetic properties, 1J85 permalloy was deposited on molybdenum substrate by electron beam freeform fabrication to achieve magnetic shielding effect for molybdenum substrate. The magnetization of molybdenum substrate was increased from 0.04 emu/g to 8.96 emu/g after depositing permalloy layer, corresponding to the decr...

The inhibitory effect of the second phase on dislocation movement has long been deemed as a great contribution to the strengthening of alloys. We investigate the electronic behavior at the α-Al matrix/second phase interface to explore its inhibitory effect on dislocation movement. This work focuses on the difficulty in dislocation movement on the i...

High-entropic weld was acquired by adding high-entropy alloy interlayer into molybdenum/Kovar alloy electron beam welded joint to optimize the mechanical properties. The tensile strength of joint was up to 358 MPa when the high-entropy alloy interlayer was 1.0 mm thick, corresponding to the increase of 87% compared to the only 191 MPa of the joint...

The nanocrystalline metal material has been an investigation hotspot due to its excellent mechanical property. The high content of grain boundaries (GBs) in microstructure is the key factor affecting its fracture behavior during service. Therefore, it is essential to investigate the effect mechanism of nanoscale GB on crack propagation. In this stu...

In this work, laser metal deposition (LMD) technique was applied to fabricate SiCp/AlSi10Mg composites. Innovatively, the effect of SiCp of different scale (micron, submicron and nano scale) on the microstructure and mechanical properties was studied. With the decrease of SiCp size, the reaction between SiC and aluminum matrix was more intense, and...

A R T I C L E I N F O Keywords: In situ heat treatment 1 J85 permalloy Soft magnetic properties Electron beam welding Local misorientation A B S T R A C T Considering the deterioration of the soft magnetic properties of permalloy welded joints, a method of electron beam welding with in-situ heat treatment was investigated which provided improved so...

Electron beam freeform fabrication Magnetic shielding effect Residual stress A B S T R A C T In view of the excellent soft magnetic properties, 1J85 permalloy was deposited on molybdenum substrate by electron beam freeform fabrication to achieve magnetic shielding effect for molybdenum substrate. The magnetization of molybdenum substrate was increa...

Firstly, by analyzing the response of Charpy V-notch specimen impacted by pendulum, the relationship between specimen geometry, material properties, and impact energy is established and simplified, and the mathematical model for evaluating impact energy of specimens with different sizes is established. Then, the effectiveness of the model through a...

Evaluating the welding residual stress and deformation in a reasonable and reliable way is the perquisite of ensuring the quality of weldments. Therefore, in this paper, an artificial neural network model is developed for the prediction of welding residual stress and deformation produced in Electro-gas welding using C++ language. The plate thicknes...

In this paper, we present an improved multi-order parameter model for multi-component model of polycrystalline solidification. We introduce an interpolation function in the phase field dynamical equation to obtain controllable grain boundary energy at large undercooling. The same interpolation function is also employed in the kinetics coefficient t...

The partial weak bonding phenomenon induced by unsuitable welding parameter often occurs at the joint interface of Al/Cu dissimilar friction stir welding (FSW). Diffusion time, temperature and pressure are the main factors that affect the diffusion behavior at interface. Therefore, molecular dynamics (MD) simulation is used to investigate the influ...

The metal-thermoplastic hybrid structure has been widely employed in aviation and aerospace industry. In this work, we developed a feasible way of laser surface texturing to address the poor adhesion between PEEK and 6061-T6 aluminum alloy. With the laser surface modification on 6061-T6 aluminum alloy, the PEEK/6061-T6 friction lap joining strength...

Introduction As an important advanced functional material, the memory effect of nitinol shape memory alloy (SMA) is the focus of research. According to the current research, the memory function of the alloy decreases after welding, and there is no sufficient explanation for the phenomenon. Objectives For the problem, this research is to explore th...

This work aimed to design an undermatched lap joint that has an equal load-carrying capacity (ELCC) with a traditional equalmatched joint under out-of-plane bending. A weld strength calculation method was proposed based on the similarity of a lap joint and a T joint, as shown using linear elastic finite element (FE) analysis, and then applied in th...

A brittle reaction interface in molybdenum/Kovar joint acquired by electron beam welding-brazing, which consisted of three zones, was concretely analyzed with respect to microstructure evolution. Zone A was composed of α-Mo and σ (FeMo) intermetallic that was the origin of brittleness. The eutectoid structure in zone B was identified as α-Fe + μ (F...

Casting defects in the ZL210 aluminum alloys were repaired via a solid-state welding method named active-passive filling friction stir repairing (A-PFFSR). Effects of plunge speed on microstructures and mechanical properties of repaired joints were investigated based on a six-spiral-groove pinless tool. Casting defects were firstly machined into a...

The phenomenon of joint softening often occurs in the fusion welding process of Al–Cu–Mg alloy, which predominately derives from the grain coarsening within the joint. But in this paper, it is pointed out that the decrease in the number and proportion of strengthening phases caused by element burning is also one of the causes. The mechanism of perf...

As a light-weight and high-strength structural material, aluminum alloy has become an irreplaceable metal material in the aerospace field. In this paper, 25 mm thick Al-Cu alloy (2A12) was welded by electron beam. The welded joints softened leading to the hardness and tensile strength of the joint decreased. In view of the decrease of mechanical pr...

To eliminate the casting defects in the ZL210 aluminum alloys, the active–passive filling friction stir repairing (A-PFFSR) was used. Shoulder morphologies on the surfaces of the pinless tools were designed and optimized to improve the mechanical properties of the repairing joints. The detailed microstructures, interface behaviors, microhardness, a...

In this work, T23 steel was treated by two thermal cycles, to simulate the second heating process in coarse grained heated affected zone (CGHAZ) of weld. Meantime, the effect of microstructure evolution on reheat cracking sensitivity was investigated by using strain-to-fracture (STF) tests. It was found that the second thermal cycle procedure could...

Metal matrix composites have been developed to overcome the urgent demand of light-weight design. High entropy alloys (HEAs) are newly emerged as a new kind of potential reinforcement for metals due to their outstanding physical and mechanical properties. Here, a kind of novel Al matrix composite reinforced by Al0.8CoCrFeNi HEA particles was fabric...

Friction rivet joining was proposed to replace toxic aldehyde-based adhesives for the joining of wood-metal hybrid structures towards high mechanical performances. Polymer rivets were utilized for superior mechanical performances. Three biphasic interfaces among woods, metals, and polymers were achieved reliably with mechanical interlocking and che...

Interest in aluminum matrix composites has grown with their potential applications as engineering materials due to its high specific strength. However, there are several major obstacles remaining in the fabrication: High production costs, non-uniform distribution of reinforcements, grain coarsening of matrices, and poor interfacial reaction. In thi...

The diffusion bonding of Ti and Zr has been realised at an ultra-low temperature of 650 °C by nanocrystallising the substrate surfaces. The bonding temperature is about 100 °C lower than the standard diffusion bonding approach. The achieved joint shows a shear strength 112.9% higher than the joint with raw substrates.

In order to reduce the weld size of weld joints designed based on equal load carrying capacity (ELCC) further, the shape of under-matching butt joints is designed with the parameter of plastic limit loads. The realization condition of ELCC is that the plastic limit loads of the weld equals to that of the base metal. Through analysing the tensile/be...

Active-passive filling friction stir repairing (A-PFFSR) was employed to eliminate the casting defects in the ZL210 aluminum alloys. Based on a six-spiral-grooves pinless tool, effects of rotating velocity on microstructures and mechanical properties of the repaired joints were investigated. The casting defects were firstly drilled into taper holes...

A thermoplastic ABS and an aluminium alloy 6061-T6 were joined using friction lap welding (FLW). The joint characteristics were evaluated to investigate the effects of 6061-T6 surface and the welding parameters on the joint properties. ABS and 6061-T6 were joined via an interfacial MgO layer. The voids generated by thermal decomposition would affec...

Friction stir processing (FSP) was utilized to fabricate high strength and ductility Mg–6Zn alloys via the co-alloying of 1.0 Y and 0.5 Zr elements. The effect of co-alloying on microstructure and mechanical properties of the as-casted and FSPed Mg alloys were evaluated. Grain refinement and second-phase increase via co-alloying were obtained. The...

In this work, 0.8-mm-thick 2024 aluminum alloy was friction stir lap welded with the assistance of a stationary shoulder system. The joint surface formation, microstructure and mechanical properties of the welded joints were studied. The results showed that sound joints without defect could be obtained at a wide parameter range because stationary s...

Interfacial stress singularities have a great effect on the strength, stiffness, and fracture behavior of dissimilar joints. Commonly used stress singularity assessment methods are based on the two-dimensional theory of elasticity, which is too complicated for design purposes. Three-dimensional (3-D) finite element analysis results show that the tr...

The trend of light-weight structures leads to the wide application of high strength steels in engineering structures. When welding high strength steels, under-matched consumables could reduce the cold-cracking tendency, simplifying the preheating process. However, under-matched welds would sometimes make the high strength base metal pointless due t...

To construct reliable heterojunctions between metals and polymer matrix composites, friction self-riveting welding (FSRW) was proposed, characterized by multi-scale mechanical interlocking and adhesive bonding, to improve mechanical properties. Holes and porous oxide structures were pre-fabricated on the metal sheet. High-quality heterogeneous join...

A method to improve the brazing between YSZ and Ti6Al4V by femtosecond laser surface machining is introduced. The highest strength of ~150 MPa (which is 95.2% higher than that of the flat YSZ/Ti6Al4V joint) is achieved when the processing speed is 200 μm/s. To understand the strengthen mechanism of the surface machining on the joint strength, image...

The residual stress distributions as a function of depth in three different graphite/copper brazing joints: with no interlayer, with a copper interlayer and with a niobium interlayer are measured via X-ray diffraction by transmission geometry. The residual stress in all the joints is found to be generally compressive and increasing from the surface...

Refill friction stir spot welding (RFSSW) was successfully used to join dissimilar Al/Mg in this work. The effect of joining time on the microstructure and mechanical properties of the welded joints was studied. The results showed Al/Mg alloys were joined through the liquid eutectic phase caused by the stirring of tool. An obvious intermetallic com...

In this work, refill friction stir spot welding (RFSSW) was used to join 5083 Al and AZ31. The effect of rotation speed on joint formation, intermetallic compounds (IMCs), and failure load of the welded joints was mainly studied. The results showed that dissimilar Al/Mg alloys could be successfully joined by RFSSW, and defect-free joints were obtai...

Under-matched welds could minimize the tendency of cold cracking and reduce the preheating operations when high strength steels are welded. However, its low load-carrying capacity might make the high strength parent metal meaningless. With the aim of improving the fatigue limit of under-matched butt-welded joints, this work establishes a nominal st...

The residual stress distribution as a function of depth in a sapphire/Ti6Al4V brazing joint is non-destructively measured using Raman Spectra for the first time. A modified method that is suitable for brazing joints is developed to deconvolute the actual residual stress value in each depth from the measured averaged stress value. The measured in-pl...

This study was mainly concerned with the long fatigue crack growth rate (FCGR) of a new generation Ni-Cr-Mo-V high strength steel and its welded joints used in modern marine environment. Several major factors, including stress ratio, microstructure, welding residual stresses (WRSs) and specimen thickness were investigated. Results showed that the w...

Based on nominal stress, this paper proposed a fatigue life estimation method of V-shaped butt welded joints. Then, the fatigue bearing capacity of the base metal under the same fatigue load was used as design goal of the V-shaped butt welded joints and an equal fatigue bearing capacity (EFBC) design method for V-shaped butt welds was thus formed....

This paper attempted to reveal the underlying mechanism of the relaxation of welding residual stresses (WRSs) under cyclic loading. Experimental and numerical investigations have been conducted on 7N01-T4 aluminum alloy welded joints. A novel experimental method to monitor the evolution of WRSs during loading was proposed. A series of numerical mod...

β to α solid phase transformation with crystallographic preferred orientation in TA15 alloy was simulated using virtual front tracking modified cellular automaton (CA) model. Transformation kinetics is resolved by coupling of interface moving and solute diffusion equations. Simulated phase transformation kinetics and microstructure exhibit desired...

A computationally efficient quantitative phase field formulation is used to investigate the sidebranching dynamics under different transient conditions in directional solidification for realistic parameters of a dilute alloy. The sidebranch growths where the pulling speed or temperature gradient increases with constant increasing rates are simulate...

A cellular automaton (CA) model coupled with Svoboda’s analytic solution of diffusional phase transformation was established to simulate β-α transition in titanium alloy. A numeric definition of diffusion, mixed and interface mode transformation is put forward and simulated by the newly developed CA model. To the best of our knowledge, this is the...

Dynamic evolution of initial instability is investigated by an analytic model obtained by modifying the theory of Warren and Langer [Phys. Rev. E 47, 2702 (1993)] and the quantitative phase-field model in directional solidification under transient conditions for realistic parameters of a dilute alloy. The evolutions of tip velocity and concentratio...

It is of great importance to study how the process parameters influence the continuum flow properties and mesomicrostructural features during friction stir welding (FSW) of titanium alloys. In the present paper, microstructure evolution of dynamic recrystallisation (DRX) was simulated by cellular automaton method based on metal plastic flow analysi...

A visco-elastic-plastic constitutive model for welding of A7N01-T6 aluminum alloy was established, considering the welding thermal temperature and deformation history. The model used elastic-mixed hardening plastic and creep equation to describe the strain hardening at low temperatures and strain softening at high temperatures, respectively. And it...

A virtual front tracking modified cellular automaton (CA) method is applied to simulate solid phase transformation with a specific crystallographic preferred orientation in a TA15 alloy, to eliminate the dependence of the traditional CA method on space meshing. Simulation results demonstrate the capabilities of the new model in growth anisotropy mo...

This paper has established a viscoelastic-plastic constitutive model for A7N01-T6 alloy welding, which is temperature and deformation history dependent. The model uses elastic mixed hardening plastic and creep equation to describe the strain hardening at low temperatures and strain softening at high temperatures, respectively. Then it is applied fo...

In order to understand the technological characteristics of dual laser-beam bilateral synchronous welding (DLBSW) and optimize the technological matching parameters, both finite element numerical simulation and experimental study were carried out for the T-joints which were composed of 6156 aluminum alloy bottom plates and 6056 aluminum alloy strin...

This paper presents a customized simulation system for analyzing welding temperature field, which is based on Finite elementary Analysis software MSC.Marc. The system has the functions of robustly hexahedral meshing, automated loading of dynamic heat source models for various welding methods and convenient post-processing for welding temperature fi...

Based on the estimation of the critical hydrogen pressure and concentrations required for hydrogen-induced delayed cracking in high-strength steel, the conclusion that welded joints are hydrogen pressure microcracks body can be drawn under certain conditions. Through the analysis of the relationship between the microstructure evolution of welded jo...

In this paper, cold bending properties of Q620-CF steel butt joints were analyzed based on the finite element method. Finite element analysis (FEA) results indicate that the flush under-matched butt joints have lower bending properties than the flush equal-matched butt joints, but under-matched butt joints with definite reinforcement shape can get...

The problem concerning the curve welding paths often exist in the analysis on both welding thermal process and stress deformation for complex structures. The modeling for the heat source of dynamic welding is difficut to be realized. In order to solve the above-mentioned problem, the automatic modeling method for the heat source of curve welding pa...

To accurately design the joint shape and amply reflect the load-carrying capacity of butt joint with defects, the influences of joint shape parameters on stress intensity factor (SIF) of butt joint with single-edge crack are provided with finite element method (FEM) in this study. SIF expressions for two typical butt joints with single-edge crack c...

In order to improve the fracture resistance of undermatched butt joint, the influence of joint shape parameters on the stress intensity factor (SIF) of undermatched butt joint with mode I centre crack was studied, and the solution of SIF was obtained by combining the analytical method with the finite element method as well. The results are useful t...

In this paper, the stress intensity factor (SIF) expression for center-cracked butt joint under tensile load was derived and the SIF differences with or without considering weld reinforcement were discussed. For the sake of discussion, the curve of weld reinforcement is regarded as circle, the reinforcement circle and the other two weld toe smooth...

TA15 airplane wall panels are used widely in aircraft manufacture, which consist of some reinforced ribs and a motherboard. Therefore, welding sequences of different reinforced ribs directly determine distortion and residual stress distributions of welding wall panels, and then affect the structure service performance. Therefore, it is important to...

Titanium-steel composite plate finds its application to constructing large pressure vessels normally used for storage and processing petrochemicals. The present study aims to calculate the stress-strain distributions in different types of welding joints possibly used in a pressure vessel which is built with a TA2/16MnR composite plate. A finite ele...

A new thinking was introduced that combine finite clement analysis(FEA) for welding process simulation with virtual manufacture(VM), it is significant research according to comparison of FEA for welding process and VM, parameters input by FEA pre-processor and by VR technology, FEA results cab be shown by FEA post-processor and by VR technology. Th...

The weldability of some material is analyzed with simple calculating program in this paper, and weldability testing data are shared through database system. The welding procedures are designed with help of expert systems, and the knowledge is shared among welding engineers. Not only the preparing progress of the welding documents is completed with...

Since loading complex and dynamic heat source is a difficult job during welding simulation process, methods are studied to add the load automatically. Firstly, an expert module for selecting welding heat source model is founded based on simulation knowledge and experiences. Secondly, a method named as "High order routine" is presented, which create...

A software package has been developed which can simulate and predict the weld solidification cracks with three dimensional FEM. It consists of pre-processing, post-processing and solidification cracks predicting subsystem. The post-data treatment of software package for three-dimensional simulation and prediction of the weld solidification cracks c...