Li Qun li Li

Harbin Institute of Technology | HIT · State Key Lab. of Advanced Welding and Joining Technology

The in-service behavior of low-pressure rotor components can potentially be impacted by the residual stress distribution of cladding layers. To predict the evolution of residual stress in a multi-pass multi-layer cladding, a thermal-metallurgical-mechanical model that incorporates the effect of solid-state phase transformation (SSPT) is proposed. I...

In order to reduce porosity and improve welding quality during laser welding with narrow gap of 5A06 aluminum alloy, a laser oscillation method was applied in this study. By comparing the welds with different scan paths, it was found that the laser oscillation with cycloid path could restrain the formation of pore defects, improve the surface appea...

Microcracks initiated and propagated behaviors in Al/steel interface determined interfacial bonding strength and this was observed by in situ scanning electron microscopy (SEM) technology. Interface without or with discontinuous intermetallic compound (IMC) had low bonding strength owing to insufficient metallurgical bonding. When interface was joi...

This study investigated the dynamic behavior of a keyhole and molten pool under circular and zig-zag oscillating paths for laser welding on galvanized steel. A large variation in the length of the keyhole and a bulge in the molten pool resulted in more spatters in the case of a circular oscillating path, whereas a little spatter was observed in the...

The porosity with chain-like shape is found in high power laser welding of thick steel plate, which are periodically distributed at the lower and middle parts of the weld and parallel to bottom fusion line. A 3D numerical model is developed to reveal the effect of laser energy absorption and transfer, keyhole fluctuation, molten pool flow and solid...

In the narrow-gap multi-layer welding of thick Ti-6Al-4V titanium alloy sheets, reducing the number of filling layers can effectively improve the welding efficiency and reduce the possibility of interlayer defects. In order to explore the changes in the microstructure and properties of the weld after reducing the number of filling layers, Ti-6Al-4V...

The effect of inhomogeneous composition of Cr and Fe on morphology and formation mechanism of passive film was investigated. A bi-layer structure passive film with a Cr2O3 inner layer and a Fe2O3 outer layer obtained on EHLA coating. The passive film is heterogeneous (thickness, compactness) between inter-dendrite and dendrite core due to the eleme...

In this research, satisfactory Al/steel butt joint was obtained by the dual spot laser welding-brazing technology with various spot configurations (+45o biased to steel side, in-line, -45o biased to Al side). The results showed that the interfacial IMC (Intermetallic compound) were composed of η–Fe2(Al,Si)5 and θ–Fe(Al,Si)3 for three joints. The in...

In this paper, a computational fluid dynamics model considering zinc evaporation was innovatively established to investigate the interaction between zinc vapor and laser keyhole in both zero-gap and small-gap conditions. Under the zero-gap condition, it was observed by a high-speed camera that the entrance of zinc vapor gas into the keyhole had the...

Chemical-etched surface texturing is of great potential for processing technologies involving solid/liquid wetting due to its simplicity, efficiency, and applicability. In this study, the wetting behaviors of 4043 aluminum alloys on different 301 L stainless steels in the as-received and two chemical-etched textured states were investigated by the...

An in-situ VC reinforced composite coating was fabricated on a mild steel substrate by using extreme high-speed laser cladding (EHLA) for the first time. The composite coating was defect-free and metallurgically bonded to the substrate. The composite coating reaped the benefits, that small-sized in-situ VC (<2 μm) was densely and uniformly distribu...

Due to the difference in heating time, temperature distribution and environment, it is insufficient to explain the interfacial behavior under non-isothermal conditions relying on the isothermal wetting mechanism. In this study, the laser-induced dynamic wetting process of stainless steel by Al alloy was investigated. The wetting behavior was record...

Dual-phase steel DP590 and carbon fibre reinforced polymer (CFRP) were successfully joined by laser welding. Experiments and numerical simulations were performed to clarify the influence of laser power on the joint characteristic, bonding mechanism and fracture behavior. The results indicate that the melting width and depth of CFRP increased with t...

The present work investigates dissimilar fiber laser joints between QP1180 and TRIP780 steels. The scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD) characterizations were conducted to study the detailed microstructures of each region of the joints. The result showed that a large volume fraction of tempered martensit...

Compared with isothermal wetting, laser-induced wetting behavior exhibited a significant contrast within the spreading mechanism owing to the short thermal cycle and migration driven by the thermal gradient. In this study, laser-induced wetting behavior of AlSi5 alloy on Ti6Al4V substrate was investigated. The process was captured by a self-built d...

Due to the shorter heating time and strongly nonisothermal nature of laser-heating, laser-induced wetting behavior exhibits a huge difference when compared to isothermal wetting. In this study, the laser-induced wetting behavior of AlSi5 alloys on Ti6Al4V substrates with various microtextures was investigated. The role of microtexture in wetting wa...

Scaling up commercial hydrogen production by water electrolysis requires efficient oxygen evolution reaction (OER) electrodes that can deliver large current densities (more than 500 mA cm−2) at low overpotentials. Here, a highly active and conductive shell‐based cellular (Shellular) electrode is developed through a strategy of embedding nanocrystal...

A 3D model was established to accurately simulate the internal and external powder stream characteristics of the coaxial discrete three-beam nozzle for laser metal deposition. A k-ε turbulence model was applied in the gas flow phase, and powder flow was coupled to the gas flow by a Euler-Lagrange approach as a discrete phase model. The simulated po...

The inhomogeneous microstructure and fatigue crack propagation of 30 mm thick-section high strength steel welded joint by double-sided hybrid fiber laser-arc welding were investigated in detail. The results indicated that the average effective grain size of the laser zone was only 1/2 of that of the arc zone, due to the faster cooling rate of the l...

Dissimilar weld joints of QP980 and TRIP800 were fabricated by a fibre laser. The microstructure and mechanical properties of dissimilar weld joints were studied. The tensile properties of weld joints were not influenced by the narrow softening zone with a less reduction in hardness of ∼25 HV from the QP980, which contributed to fracture in TRIP800...

The new generation pillow plate heat exchanger (PPHX) is a type of PHXs with a complex wavy structure with desirable thermal-hydraulic characteristics. For the main structure of PPHX, edge welding joints are usually a common and economical design. However, the stress concentration and presence of corrosive media often lead to premature failure of w...

Numerical simulations and experiments are conducted to investigate the influence of three different scan paths, namely straight, sine, and cycloid, on the flow dynamics and weld formation during the laser welding of 5A06 aluminum alloys. The cycloid scan path produced molten pools with the largest dimensions, most regular morphology, and lowest tem...

The correlation between plasma plume and laser energy transmission during vacuum laser welding of aluminum alloy was discussed in this study. The electron temperature and density of the plasma plume were calculated by spectroscopic analysis. The refraction and attenuation of laser energy were studied with a probe laser. The scattering effect of nan...

The design of metastable retained austenite is the key issue to obtain nano bainitic steel with high strength and toughness. In this study, nanostructured Fe-based bainitic coatings were fabricated using laser cladding and following isothermal heat treatment. The microstructures and mechanical properties of the laser cladded coating were investigat...

In order to explore the synergetic effect on the process combination of pulsed laser and pulsed MIG hybrid welding, two kinds of coupling modes were performed by modulating the laser power to synchronize the arc current. The results showed that under the in-phase coupling mode, the addition of a high power laser during the peak period of the arc cu...

Laser welded–brazed Al/steel lapped joint was successfully obtained under various shielding gas contents (pure Ar, CO2+Ar and pure CO2) with laser power of 2000W. Influence of shielding gas contents on weld formation, interfacial microstructure and tensile–shear strength was investigated. The addition of CO2 in the shielding gas would not only enha...

The corrosion resistance of 431 stainless coatings produced by a novel surface modification technology (EHLA) was analyzed. As the cladding speed increased, the dendrites became more refined and the composition distribution was more uniform. Corrosion tests showed that better corrosion resistance was achieved with a higher cladding speed. The unifo...

Al/steel butt joints were successfully obtained using a dual–spot laser welding–brazing process with different R (R = EFe:EAl = 4:6, 5:5, and 6:4; EFe and EAl represented the energy ratios of the laser near steel and Al, respectively). The molten filler metals wet and spread well along the front and back surfaces of the steel when R was 5:5 and 6:4...

The stress corrosion resistance of 30 mm-thick narrow-gap rotating laser welding (NG-RLW) 5A06 aluminum (Al) joint was investigated by slow strain rate testing (SSRT). The results show that the average ultimate tensile strength (UTS) of the joints in 3.5% NaCl solution is about 11% lower than that in air, and its elongation is only half of that in...

The morphology and crystallography of the lath martensite in the weld metal of high strength steel by double-sided hybrid fiber laser-arc welding were investigated. The lath martensite was found to have Kurdjumov-Sachs orientation relationship. The amount of the lath martensite in the block was affected by the cooling direction of the weld pool. Al...

High quality 431 steel coatings were prepared on a 27SiMn substrate by extreme-high-speed laser cladding (EHLA) and conventional laser cladding (CLA), respectively. The cladding speed of the EHLA process was 150 m/min, and the surface rate could reach up to 1.14 m²/h, which is four times higher than that of the CLA process. The microstructure of th...

Thin-walled specimens with more than 150 layers were deposited by laser metal deposition without cracks and concaving deformation. The microstructure in each layer could be divided into three zones according to the morphology. The homogeneity deteriorated with the rising of the input. The tensile strength dropped 29.7% when the porosity increased f...

Laser welding under subatmospheric pressures exhibits significant potential in the field of large-scale structure connections. In this study, a set of disk laser welding experiments are performed on 35-mm-thick 5A06 aluminium alloy under various ambient pressures. The influence of ambient pressures on weld formation, plasma plume behaviours, micros...

The design and development of highly efficient three-dimensional (3D) supports for electrocatalytic reactions at the boundary of gas-liquid-solid phases are vital in lowering their energy losses. However, 3D supports with geometrically-complex design are very difficult to prepare directly by conventional methods. Here we have demonstrated that high...

High roughness of metal structures made by selective laser melting restricted their extensive applications. A strategy of overpotential electrochemical polishing was developed for effectively smoothening three-dimensional (3D)-printed surfaces, particularly for removing sticking particles. Average surface roughness of 0.18 µm was achieved with a sm...

In order to explore ultra-high fber laser welding characteristics of 5A06 aluminum alloy, bead-on-plate welding was performed under atmospheric and subatmospheric pressure with the maximum laser power of 30 kW. The results showed that it was very difcult to carry out a defect-free weld joint with a satisfactory penetration depth under atmospheric p...

In order to meet the requirements of alignment capability, gap tolerance and welding track control, dual-beam laser welding has been put forward to weld tailored blanks with different thicknesses. The arrangement mode and power ratio of dual-beam laser determine the heat transfer and temperature field distribution, and then influence the weld profi...

Numerous studies have primarily focused on the corrosion mechanism of zirconium alloy base metal. However, the corrosion resistance of weld beads or seams is of vital importance in the degradation of structural components in the reactor. In the present work, the corrosion resistance of the fusion zone and base metal of laser welded zirconium alloy...

Electron beam melting (EBM) is an established powder-bed additive manufacturing process for small-to-medium-sized components of Ti-6Al-4V. For further employing EBM on fabricating large-scale components, an effort has been made by joining EBM-built Ti-6Al-4V plates to wrought counterparts using laser welding, and the welding angles between EBM buil...

TiC particle (TiCp) reinforced Ti6Al4V (TiCp/Ti6Al4V) titanium matrix composites with coated powders (TiC: <10 μm) and small-sized (TiC: 25–45 μm), medium-sized (TiC: 45–75 μm) and large-sized (TiC: 75–100 μm) mixed powders were produced by laser melting deposition (LMD). The influence of TiC particle size on the microstructure and tensile properti...

Laser welding–brazing Al/steel with different Zn–Al filler metals was performed. Experiments and thermodynamics calculations were conducted to analyze microstructure evolution and elemental diffusion behavior, respectively. The interfacial intermetallic compounds (IMC) was composed of dominating layered η–Fe2Al5Zn0.4 phase and two different types o...

A reliable numerical model is developed to predict the deformation of mismatch and normal butt-welded joints after laser and gas metal arc hybrid welding (Laser-GMAW). A smaller deflection is produced in the mismatch joint as a result of a more uniform weld profile along the thickness direction, while a larger shrinkage deformation is obtained as a...

Powder-based laser deposition technology has widely used for parts coating, repairing and additive manufacturing. The quality and efficiency of laser deposition largely depends on the powder stream controlling. For some special laser deposition processing, such as ultra-high-speed laser cladding, inside laser cladding, FGM(Functionally Graded Mater...

A turbine component with 130 blades requests high dimensional precision to ensure the assembly requirements. The dimensional precision is significantly influenced by welding distortion. In this research work, welding distortion in the turbine component by electron beam welding was predicted through elastic finite element method based on inherent st...

The laser-arc hybrid welding of HG785D high-strength steels is performed and the effects of laser power and wire feeding speed on the hybrid welding process under different heat source orders are investigated. The dynamic behavior of plasma in the hybrid welding process is investigated. The electron temperature and electron density in plasma under...

Double-sided laser beam welding of 2-mm-thick 2060-T8 and 2099-T83 aluminum-lithium alloys T-joint was performed with AlSi12 wire. Microstructure and nano-indentation hardness characteristics were studied especially in nondendritic equiaxed zone (EQZ). In comparison with the precipitates of LiAlSi, Mg2Si and Al2Cu in weld zone except for the EQZ, a...

Laser welding-brazing 2-mm-thick 6061-T6 aluminum alloy to DP590 dual phase steel in butted configuration was performed with AlSi12 filler metal. The influence of laser power on weld appearance, interfacial microstructure and tensile strength was studied. Thermal cycle at brazing interface was calculated by numerical simulation in order to clarify...

Laser welding–brazing of 6061-T6 aluminum alloy to DP590 dual-phase steel with Al-Si12 flux-cored filler wire was performed. The microstructure at the brazing interface was characterized. Fracture behavior was observed and analyzed by in situ scanning electron microscope. The microstructure of the brazing interface showed that inhomogeneous interme...

The aim of this study is to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the cap...

Transient thermo-mechanical simulation of stainless plate laser welding process was performed by a highly efficient and accurate approach-hybrid iterative substructure and adaptive mesh method. Especially, residual stress prediction was enhanced by considering various heat effects in the numerical model. The influence of laser welding heat input on...

In the present study, aluminum alloy T-joints were welded using the laser stake-welding process. In order to improve the welding quality of the T-joints, an external electric current was used to aid the laser stake-welding process. The effects of the process parameters on the weld morphology, mechanical properties, and microstructure of the welded...

A 10kW fiber laser was used to weld 10 mm thick Inconel 718 alloy, because of bad thermal conductivity and existence of high boiling point elements, a full penetration and smooth weld appearance of Inconel 718 was hard to obtain with single-pass laser welding under normal atmosphere, and there were undercut and spatters defects existed. In consider...

Laser melting deposition (LMD) technique was used to manufacture TiC particle (TiCp) reinforced Ti6Al4V (TiCp/Ti6Al4V) titanium matrix composites with TiC volume fraction ranging from 5% to 30%. The microstructure and tensile properties of as-deposited and heat-treated TiCp/Ti6Al4V composites were studied. Microstructure and tensile properties of T...

Defocused laser welding-brazing of 2-mm-thick 6061-T6 aluminum alloy and DP590 steel in butted configuration was performed with AlSi12 flux-cored filler metal. Three different groove shapes at steel side were made: square-shape, half Y-shape and half V-shape. The experimental results indicated that inhomogeneous intermetallics compounds (IMC) morph...

The aim of this study was to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the ca...

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool we...

Three different shielding gas nozzles were designed for the narrow-gap laser-MIG hybrid welding of thick-section steel. Different gas flow behaviors produced by the three nozzles exerted great effects on the welding characteristics. While using the straight-trapezium shielding gas nozzle, unstable droplet transfer behavior with spatters and welding...

Crack-free functionally graded TiC particle (TiCp) reinforced Ti6Al4V (TiCp/Ti6Al4V) composite was manufactured by laser melting deposition (LMD) technology with TiC volume fraction changing gradually from 0% to 50%. This research focuses on the relationship between the microstructure and mechanical properties (microhardness and tensile properties)...

2060 and 2099 aluminum‑lithium (Al-Li) alloys are both the candidate structural materials for Chinese C919 aircraft fuselage panels and their related welding characteristics are greatly different from those of aviation aluminum alloys and need to be studied. Double-sided laser beam welding of 2-mm-thick 2060-T8 and 2099-T83 Al-Li alloys T-joints we...

Thick aluminum alloy plate has been widely applied in various structural components. The rapid development of high-power and high-brightness lasers provides the potential for single pass autogenous laser welding of thick aluminum alloy plate. However, when the special physical factors of aluminum alloy, such as high reflectivity, high thermal condu...

In comparison with conventional laser beam welding, double-sided laser beam welding has two laser heat sources simultaneously and symmetrically loaded from both sides makes it to be a more complicated coupled heat transport and fluid flow process. In this work, in order to understand the heat transfer and fluid flow, a three-dimensional model was d...

Ti6Al4V alloy thin wall is prepared by using laser melting deposition, and the influences of process parameters on the size stability of molten pool and microstructure growth characteristics of deposited layers are studied. The temperature field of molten pool and cooling rate of melt under different process conditions are calculated based on finit...

Effect of energy ratio on weld formation and energy efficiency in the dual beam welding process was systematically studied. Molten pool behaviors under different energy ratios were observed in real time by the high speed video system. Influence mechanism of the energy ratio on dual beam laser welding characteristics was also revealed. Results show...