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Cylinders made of tantalum (Ta) and tubes made of 304 stainless steel (304SS) were successfully joined by laser welding under different offsets. The experimental results indicated that satisfactory weld formations were obtained. The fusion zone (FZ) was found to consist of the Fe-Cr solution and the Fe2Ta phase. In addition, the intermetallic compounds (IMCs) layer was generated at Ta/FZ interface. When the laser beam offset was -0.2 mm (0.2 mm laser beam offset on the 304 stainless steel side), the interfacial IMC consisted of Fe2Ta. Thicker IMC with the compositions of Fe2Ta+FeTa was generated at offsets of 0 mm (center) and +0.2 mm (0.2 mm laser beam offset on the Ta side). Numerical simulation results showed that the interfacial peak temperature would be increased when the laser beam offset from 304 stainless steel side to Ta side, which led to the thicker IMC and new generation of FeTa. The microhardness in the FZ also fluctuated since the FZ was composed of hard Fe2Ta and soft Fe-Cr solution. Tensile test results indicated that the highest value of 308.3 MPa was obtained under the laser beam offset of -0.2 mm.

The instability of rock mass induced by the deterioration and failure of rock bridge is often encountered in hard rock engineering. Under engineering disturbance, a steep and gentle stepped sliding surface is prone to forming along the rock bridges between the intermittent rock joints, which directly controls the rock mass instability modes. In order to reveal the influence of fissure angle on the fatigue deterioration and energy evolution mechanism of stepped double-flawed hard rock, the multilevel cyclic loading mechanical test were carried out on flawed marble samples with fissure angle of 10°, 30°, 50°, and 70° angles. The testing shows that rock strength, fatigue lifetime, peak strain and dissipated energy increase with increasing fissure angle and the increase rate of them becomes sharply in the high cyclic level. In addition, the increase of dissipated energy accelerates with the increase of cyclic loading level, and shows a sudden increase trend in the last cyclic loading stage. When the joint fissure angle is 10°, the dissipated energy is the smallest and the dissipated energy is the largest at 70°. Moreover, a damage evolution model based on dissipated energy is established to describe the characteristics of damage accumulation. The model is in good agreement with the experimental data and reflects the nonlinear characteristics of damage accumulation.

To improve the aging resistance of bioasphalt and explore the impact of organic nano calcium carbonate (CaCO3) on the aging resistance of bioasphalt, the thin-film oven test (TFOT), basic property test, rheological test, four components test, and infrared spectrum test were used to study the bioasphalt with different organic nano-CaCO3 contents. The results show that the addition of organic nano-CaCO3 increases the residual penetration, residual ductility, and residual softening point of bioasphalt. Within the range of test dosage, the greater the dosage, the more significant the effect is. With the increase of organic nano-CaCO3 content, the complex modulus aging index (GAI) of bioasphalt gradually decreases, and the colloidal instability index (IC) gradually decreases. When the content is 6%, the GAI of organic nano-CaCO3 modified bioasphalt is less than that of matrix asphalt. The nanoscale super large specific surface area of organic nano-CaCO3 has an adsorption effect on the light components in bioasphalt, which slows down the volatilization loss of light components and the oxidation process of asphalt. The addition of organic nano-CaCO3 helps to reduce the change rate of the carbonyl index and sulfoxide index.

Here, in order to develop the metallic materials with excellent relationship between strength and toughness for application, the FeCoCrNi + FeCoCrNiAl-laminated high-entropy alloys (HEAs) had been fabricated by laser melting deposition (LMD) additive manufacturing technique. The process parameter databases for FeCoCrNi and FeCoCrNiAl HEAs were built by orthogonal experiments and statistics method, which helped to select the optimised process parameters for the two HEAs. Then, the differences in the forming process, phase structure, and grain morphology of FeCoCrNi and FeCoCrNiAl HEAs were systematically investigated during the fabrication of the FeCoCrNi + FeCoCrNiAl-laminated HEAs. The results show that variations in surface tension, wettability, and other physical properties between the two HEAs led to significant differences in their LMD processes. Al not only influenced the fabrication process of both HEAs, but also promoted the phase transition from FCC (FeCoCrNi) to BCC (FeCoCrNiAl). In addition, Al also acted as a strong limiting factor to inhibit the effect of supercooling on the grain morphology, which transformed from coarse columnar grains to fine equiaxed grains. The columnar grains, with a preferred orientation in the FeCoCrNi-deposited wall, promoted the suppression of the inhibitive effects of the phase structure and strong limiting factor, led to the growth of the columnar grains in the FeCoCrNiAl-deposited wall, and helped achieve long-distance continuous growth of columnar grains across the interface in the subsequently deposited wall. The methodology used in this study could be meaningful for the exploration of process parameters of LMD, and the discoveries of grain characteristic help to understand the microstructure transition in laminated heterogeneous HEAs fabricated by laser additive manufacturing.

The immunological role of exosomes in autoimmune encephalitis (AE) remains uncharacterized and not examined. In this study we ought to determine whether exosomes are generated in AE and to define the presence of cell surface neuronal autoantigens (autoAgs) in the cargo. Exosomes were isolated from cerebrospinal fluid (CSF) from 12 patients with anti-N-methyl-d-aspartate (NMDA) receptor encephalitis, 8 patients with anti-gamma-aminobutyric acid-B (GABAB) receptor encephalitis, 8 patients with anti-leucine-rich glioma-inactivated 1 (LGI1) encephalitis, 8 patients with anti-contactin-associated protein-like 2 (CASPR2) encephalitis, 10 patients with anti-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid 1,2 (AMPA) receptor encephalitis and 30 control individuals negative of antibodies against neuronal autoAgs. Western blot demonstrated that CSF or sera derived exosomes from AE contained specific neuronal autoAgs in protein aggregates, however, control subjects had no detectable levels of these neuronal autoAgs. In addition, development of antibodies against NMDAR, GABABR, LGI1, CASPR2, and AMPAR were detected in the sera after 30 days immunization of C57BL/6 J mice with exosomes isolated from antibody positive AE patients; Enzyme-linked immunospot (ELISpot) assay demonstrated increased frequency of neuronal autoAgs-specific IL-17 and IFN-γ in splenocytes from AE derived exosomes immunized mice. We concluded that exosomes expressing neuronal autoAgs were present in CSF from antibody positive AE patients, and we propose these exosomes carrying neuronal autoAgs would play an important role in the immune pathogenesis of autoimmune encephalitis.

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 temperature gradients. And the shallowest keyhole with the highest stability and the lowest temperature is produced under this condition, which has the effect of reducing and homogenizing the distribution of the fluid velocity. The most complicated vortices are obtained when the cycloid scan path is used. Porosity ratios of 5.5, 4.9, and 0.59 are obtained when the scan paths are straight, sine, and cycloid, respectively. The large and stable molten pool, the shallow keyhole, as well as the low and highly homogeneous melt flow velocity and the complicated vortices, contribute to reduction in porosity formation.

The role of secreted exosomes during dopaminergic (DA) neuron differentiation is still unknown. To investigate the roles of exosomes in DA neuron fate specification, we profiled exosomal microRNAs ...

Oscillating laser welding of 2-mm-thick 6061-T6 aluminum alloy and AISI304 steel in overlap configuration was performed under various oscillation amplitudes of 0, 3, and 5 mm. The experimental results indicated that the welding window of Al/steel dissimilar joints was improved with increasing oscillation amplitudes. The beam oscillation broadened weld width and interfacial bonding width while reducing weld depth. In the joint produced under 0-mm oscillation, a multi intermetallic compound (IMC) layer formed with a thickness of about 90 μm. In the joint produced under 3-mm oscillation, the IMC layer with the compositions of η-Fe2Al5+block-shaped θ-Fe4Al13) was obtained and its corresponding thickness reduced to 20 μm. When the oscillation amplitude further increased to 5 mm, only a η-Fe2Al5+little θ-Fe4Al13 layer with a thickness of 5 μm generated. Simulation results for the temperature history indicated that an oscillating laser beam would disperse laser energy, restraining the steel penetrating. Besides, dispersed heat energy depressed the melting of lower aluminum sheets and interfacial element diffusion. Thus, the formation of IMCs was suppressed. The limited IMCs and increased bonding width led to an improvement in the tensile–shear properties. The maximum fracture load of the joint under 5-mm oscillation was 185 N/mm, which was twice higher than that of joints welded without beam oscillation. Less Al atoms dissolved into the fusion zone under beam oscillation, resulting in lower microhardness and better toughness. Fracture locations changed from the fusion zone to the interface due to weakened steel penetration and improved toughness.

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 enhance the total fusion volume but also improve the wettability of molten filler. Interfacial microstructure observations showed that addition of CO2 in the shielding gas would thicken the interfacial IMC. Continuous layered η–Fe2(Al,Si)5 and serration shaped θ–Fe(Al,Si)3+τ5–Fe1.8Al7.2Si was newly formed. In addition, higher peak temperatures were produced with the increase of CO2 volumes, which was proven by numerical simulation results. Higher laser energy absorption for CO2, alternation of melt flow pattern and smaller thermal conductivity of CO2 were responsible for these changes. Highest average tensile–shear strength of 163MPa was obtained under the shielding gas content of 50 %Ar+50 %CO2 when laser power was 2000W.

Carbon fiber-reinforced composites are widely used in automobile, aerospace and military lightweight manufacturing due to their excellent mechanical properties such as light weight, excellent fracture resistance, corrosion resistance and wear resistance, etc. However, because of their high hardness, anisotropy and low interlayer strength characteristics, there are many problems with machine carbon fiber-reinforced composites with traditional methods. As a non-contact processing technology, laser machining technology has lots of advantages in carbon fiber-reinforced composites processing. However, there are also some defects produced in laser machining process such the heat affected zone, delamination and fiber extraction due to the great difference of physical properties between the carbon fibers and the resin matrix. To improve the quality of carbon fiber-reinforced composites laser machining, lots of works have been carried out. In this paper, the research progress of carbon fiber-reinforced composites laser machining parameters optimization and numerical simulation was summarized, the characteristics of laser cutting carbon fiber-reinforced composites and cutting quality influence factors were discussed, and the developing trend of the carbon fiber-reinforced composites laser cutting was prospected.

AMS-02 has been measured with unprecedented precision data for the positron flux. These data show that there is an excess of cosmic positrons detected for energies above 10 GeV with respect to the well known secondary production which is due to the collision of cosmic rays with the atoms of the interstellar medium. In this paper we have investigated the possibility that the positron excess is due to the acceleration of positrons and electrons from pulsar wind nebulae. We have first made the assumption that only one pulsar, Geminga, dominates the production of positrons detected at Earth. We find that a spectral index for the injection spectrum of e + is needed to fit the data but an efficiency for the conversion of pulsar energy into positron of about 100% is required. This is unphysical since also electrons should be accelerated with the same amount. We have done the more realistic case where all the pulsars reported in the ATNF catalogue produce positrons. We have demonstrated that this case fits well the data with efficiency values of the order of 10-20%. These results imply that pulsar wind nebulae in the Galaxy are likely the main contributors to the positron excess.

Joining dissimilar metals, such as Al to steel, in butt configuration was successfully realized by laser powder deposition. Satisfactory weld appearances were produced when the laser powers were 1800 W and 2200 W. No obvious interfacial reaction layer was generated when the laser power was 1200 W, and only τ5-Fe1.8Al7.2Si phase (1–3 μm) was produced when the laser power was 1500 W. A 3-μm-thick τ5-Fe1.8Al7.2Si phase, 5-μm-thick mixed intermetallic compound (IMC) (θ-Fe(Al,Si)3 + τ5-Fe1.8Al7.2Si phases) and 1-μm-thick τ5-Fe1.8Al7.2Si phase were produced, respectively, at the top, middle and bottom regions when the laser power became 1800 W. Additionally, 8-μm-thick and 10-μm-thick mixed IMC (η-Fe2(Al,Si)5 + θ-Fe(Al,Si)3 + τ5-Fe1.8Al7.2Si) phases were produced, respectively, in the top and middle regions while only a 5-μm-thick θ-Fe(Al,Si)3 + τ5-Fe1.8Al7.2Si phase was produced in the bottom region when the laser power increased to 2200 W. Numerical results showed that the highest peak temperature in the middle region led to the thickest IMC in this region. Highest tensile strength (194 MPa) and largest fracture displacement (0.35 mm) were both obtained in the joint produced when the laser power was 1800 W. Poor weld formation, a lack of an IMC layer at the interface and a newly formed η-Fe2(Al,Si)5 phase were all harmful for the tensile properties of the joint.

Monodisperse semiconductor single-crystal spheres hold great potential for building photonic crystals owing to their higher refractive index and smoother surface than their corresponding polycrystalline ones. However, the difficulty in obtaining isotropic growth with a slower rate of nucleation and growth makes it challenging to synthesize highly uniform single-crystal spheres with sizes of several hundred nanometers. Herein, we designed a room temperature two-step reductive approach in the presence of both sodium citrate and PVP as capping ligands in a H2O/ethylene glycol (EG) mixed solvent. By this method, real monodisperse single-crystal solid Cu2O spheres were obtained. The key functions of EG, sodium citrate and PVP in the formation of single-crystal Cu2O spheres were investigated. The mechanism of isotropic growth of the monodisperse single-crystal solid Cu2O spheres is discussed in detail. The results indicate that copper citrate complex, PVP, hydrogen bonding and appropriate viscosity are all indispensable for isotropic growth. The diameter of the as-prepared single-crystal solid Cu2O spheres could be tuned from 168 nm to 265 nm by varying the amount of sodium citrate. The SEM and TEM images revealed that the prepared Cu2O spheres had a narrow size distribution and are single-crystal solid spheres. Using Cu2O spheres with different diameters as building blocks, amorphous photonic structures with vivid brown-red, green and pink colors were fabricated by a spray-coating method. Our results provide a method for preparing single-crystal solid semiconductor spheres, unveiling the possibility of using single-crystal spheres as building blocks for creating structural color.

Detection of methanol is a significant segment for body health and work safety in the production of chemical industry. However, there hardly exists highly selective methanol detection system with green environment for vapor or liquid adaptability, as well as large linear relationship. A facile wearable vapor/liquid amphibious electrochemical sensor for monitoring methanol has been carried out for the first time in this Article. This wearable methanol sensor was fabricated by using a simple screen-printing technology for accomplishing a microdevice platform, showing good linear relationship, high selectivity (multiple volatile chemical compounds), reliable repeatability, good stability, and excellent stretching and bending performance (nitrile glove-based sensor) without pretreatment or adding any polymers into inks. Owing to its good environmental adaptability of vapor or liquid and various sensing behaviors (high sensitivity and wide linear range) by being modified with different content of platinum catalyst, this methanol sensor would have tremendous potential application for environmental monitoring on smart wearable devices when employed based on various platforms (such as PET, cotton, and nitrile gloves).

Dissimilar lap joining of magnesium alloy to titanium alloy was performed using Ni coating by laser welding-brazing process. The influence of different Ni-coating thicknesses on microstructure and mechanical properties were investigated. In laser irradiation region, Ti3Al phase formed at fusion zone/Ti interface. In middle region, Ti3Al phase still existed at fusion zone/Ti interface, while Mg-Al-Ni ternary IMC generated at fusion zone. In weld toe region, Ti-Ni binary IMC were observed at the interface of fusion zone/Ti. The particles of Mg-Al-Ni ternary compound grew bigger and thickness of Ti-Ni compound layer increased with the increase of Ni-coating thickness. TiNi IMC transformed into (TiNi + Ti2Ni) mixtures when the Ni-coating thickness exceeded 5.8 μm. Interfacial microstructure evolution was clarified according to thermodynamic calculation results of formation enthalpy and chemical potential. The fracture load first increased and then decreased slightly with increasing coating thickness, the maximum fracture load (2430 N/cm) represented 90% joint efficiency in relation to the Mg base metal. The fracture mode changed from interfacial failure into fusion zone fracture when the Ni-coating thickness was greater than 4.0 μm. The interfacial bonding were relatively low, while the performance of fusion zone fracture was relatively high. Further increase of coating thickness has little effect on the performance deterioration. The bonding mechanism of Mg to Ni-coated Ti were illuminated.

The purpose of this study was to examine the role of cerebrospinal fluid (CSF) exosomes from patients with paraneoplastic and autoimmune encephalitis (AE).Towards this, microRNA profiling in the exosomes which were isolated from cerebrospinal fluid of 12 patients with anti-N-methyl-d-aspartate (NMDA) receptor encephalitis, 12 patients with anti-gamma-aminobutyric acid-B (GABAThere were ten miRNAs higher expressed in AE patients with anti-NMDAR encephalitis compared to those in healthy controls. Further, eight miRNAs were found to be lower expressed in anti-NMDAR encephalitis CSF derived exosomes. In addition, Endometrial cancer, p53 signaling pathway, Non-small cell lung cancer, Small cell lung cancer, Transcriptional misregulation in cancer, Basal cell carcinoma, Acute myeloid leukemia, Renal cell carcinoma, Colorectal cancer, Choline metabolism in cancer, Melanoma, Pancreatic cancer, Prostate cancer, Ras signaling pathway, Glioma, Pathways in cancer, and Proteoglycans in cancer (all p 0.01) were significantly enriched in differentially expressed miRNAs.Exosomes expressing specific miRNAs in antibody positive AE may participate as a feedback regulation in cancer development.

Objective: To explore the diagnostic value of transcranial doppler (TCD) combined with carotid ultrasound (CU) in cerebral ischemic stroke (CIS). Methods: A total of 68 patients with CIS who were treated in our hospital from September 2018 to September 2020 were selected as the research group, and another 68 patients with non-CIS admitted during the same period were selected as the reference group. Both groups underwent TCD and CU examinations to compare their diagnostic values. Results: There were no distinct differences concerning clinical data such as gender ratio, age, BMI value, smoking history, residence, and complications between the two groups (P > 0.05). The carotid artery intima-media thickening was reported at a markedly higher rate in the research group compared to the reference group (P < 0.001). It was indicated by the CU examination that the degree of carotid artery stenosis in the research group was more severe compared with the reference group (P < 0.05). The patients in the research group experienced more severe intracranial artery stenosis relative to the reference group by the TCD examination (P < 0.05). The plaque morphology of the research group was predominantly irregular, and the internal echoes were predominantly hypoechoic. The plaque morphology in the reference group was predominantly regular, and the internal echoes were predominantly isoechoic. There was remarkably higher incidence of the research group (78%) with ulcer as compared to the reference group (P < 0.05), and no marked difference was observed in the incidence of calcification (P > 0.05). The combined diagnostic approach was superior to TCD and CUS alone in the terms of accuracy, sensitivity and specificity (P < 0.001). Conclusion: TCD combined with CU can greatly improve the diagnostic efficiency of CIS, and provide more evidence for clinical therapy. It deserves promotion and use.

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 dynamic data acquisition device and interfacial microstructure evolution was explored. The mechanism for spreading was evaluated by finite element simulation, spreading dynamic and thermodynamic analysis. The wetting process was controlled by reaction product at the early stage and dominated by adsorption of elements at a later stage. The wettability was promoted with increasing irradiation time until 1.4 s. After prolonged irradiation, IMC composed of TiAl3 phase evolved from granular to rod-shape. Continue to irradiate, multiple Ti-Al phases and Ti5Si3 precipitates were produced. At central zone, Al atoms were more likely adsorbed onto Ti substrate, which facilitated the growth of Ti-Al phases. At front zone, the adsorption rate of Si atoms onto Ti substrates was accelerated and the decomposition of Si-rich phase further promoted the spreading. The elucidated relationship between wetting and microstructure could provide a reliable guide for obtaining relatively good wetting without generating over-thick compounds.

The role of secreted exosomes during dopaminergic (DA) neuron differentiation is still unknown. To investigate the roles of exosomes in DA neuron fate specification, we profiled exosomal microRNAs (miRNAs) during DA neuron differentiation of epiblast-derived stem cells (EpiSCs). There were 26 miRNAs differentially expressed (relative fold2

Photoluminescence intensity of the perovskite QDs coupled with TiO

Nanosecond pulsed laser welding of 316L stainless steel and 6063 aluminum alloy thin sheets was performed. The influence of scan line spacing on the joining process was clarified. Large explosive hole and hot cracking defects including radial cracks and arc-shaped cracks occurred in the joint caused by excessive heat accumulation when the line spacing was 0.02 mm. The joints without oxidation were obtained. The thermal-induced penetration increment (TIPI) decreased with the increase of line spacing and reached the maximum value of about 162.24% with the line spacing of 0.02 mm. Fe2Al5 and FeAl phases probably were produced at all the line spacings. However, FeAl and α-Fe phases in the form of banding structures were possibly generated only with the line spacing of no less than 0.06 mm. The shear force test results indicated that the maximum shear load of 158.8 N was achieved at the line spacing of 0.06 mm due to the large bonding area and fewer defects. Three fracture paths, namely, button pullout failure (BPF), interfacial failure (IF) and mixed fracture (MF) mode of BPF and IF were produced. The heat affected zone was the origin of BPF mode. Local deformation, pores and Fe-Al brittle phases led to the fracture paths of IF and MF.

Dissimilar AZ31B-Mg and Ni-coated Q235A-steel alloys were joined in a lap configuration using a laser welding-brazing process. The effects of the Ni coating thickness on the joint appearance, interfacial reactions and mechanical properties were investigated with the assistance of thermodynamic calculations. In the direct irradiation region, Ni atoms diffused and were accumulated near the interface due to the driving force of the chemical potential. Al atoms from the filler were attracted by the concentrated Ni atoms, which resulted in the formation of the FeAl phase. In the middle region and weld toe region, a Fe(Ni) solid solution formed at the interface. Heterogeneous reaction products were produced at the seam near the interface, varying from only the AlNi phase to the AlNi+(α-Mg+Mg2Ni) eutectic with the increase of the coating thickness. Additionally, a bulky Mg2Ni phase also formed in the matrix of Mg-Ni eutectic with a coating thickness of 40 μm. Strong mutual attraction occurred between the Al and Ni atoms at the seam, resulting in a higher driving force for generating the AlNi phase than for generating the Mg-Ni phase. All joints were finally fractured at the seam. The maximum value of the tensile-shear fracture load approached 230 N/mm with a Ni coating thickness of 20 μm, reaching an 88.5% joint efficiency relative to the Mg base metal.

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 of δ–FeZn10 phase. Scattered δ–FeZn10 phase among layered η–Fe2Al5Zn0.4 matrix was found in all joints while continuous δ–phase adjacent to steel substrate appeared in joint obtained with Zn–Al2 and Zn–Al15 fillers and disappeared in the case of Zn–Al22 filler. Thermodynamics calculation showed that Zn element preferentially diffused to the Fe–Al interface and steel substrate, and reacted with generated Fe–Al IMC and residual Fe elements, leading to the presence of Zn element in η–Fe2Al5Zn0.4 phase and the formation of δ–FeZn10 phase. The increasing Al addition in filler metals induced a more sufficient Fe–Al reaction, causing a thicker Fe–Al IMC layer and insufficient residual Fe elements at the interface. It would be harder for the Zn elements to diffuse through the η–Fe2Al5Zn0.4 layer with larger thickness. A higher Gibbs free energy of δ–FeZn10 phase compared with η–Fe2Al5Zn0.4 phase, insufficient Fe and Zn elements at the interface were all responsible for the disappearance of continuous δ–FeZn10phase. Joint with the highest tensile strength was produced with Zn–Al22 filler owing to the disappearance of continuous δ–FeZn10 phase and crack–inhibitation effect of scattered δ–FeZn10 phase among layered Fe2Al5Zn0.4 matrix.

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 result of the higher heat input compared to the normal joint. The transverse plastic strain is much larger than the longitudinal plastic strain for both joints. An interruption is observed at the bottom surface of the mismatch joint owing to the discontinuity of the weld profile. The calculated inherent deformation, based on the plastic strain, is much larger along the transverse direction than along the longitudinal direction and it is also the dominating welding deformation. The deformation of a pipe assembled with a longitudinal welding line is predicted from the calculated inherent deformation parameters. A smaller roundness (ΔR) and deflection (ΔZ) are produced in the mismatch joint due to its smaller inherent bending deformation compared to the normal joint.

6061-T6 aluminum alloy and DP590 steel were joined successfully by a laser welding–brazing process with pure Al, AlSi5, and AlSi12 filler metals. Interfacial microstructure of the joints with highest tensile strength (under laser powers of 2000 W, 2000 W and 2500 W for joints obtained with pure Al, AlSi5 and AlSi12 filler metals, respectively) were selected for comparison. The interface produced with the pure Al filler metal consisted of a thick layer of η-Fe2Al5 with scattered rod-shaped θ-FeAl3, with average thicknesses of 10.1 μm in the bottom region and 16.7 μm in the top region. When 5 wt.% Si was added to the filler metal, the interfacial intermetallic compound (IMC) components remained similar, whereas the interface thickness decreased to 3.8 μm in the bottom region and 7.5 μm in the top region. On further increasing the Si addition to 12 wt%, the interfacial IMC acquired 1.2 μm-thick τ5-Fe2Al8Si in the bottom region with 5.6-μm-thick θ-Fe(Al,Si)3 and τ5-Fe2Al8Si in the top region. The chemical potential of Si in the Fe-Al-Si ternary system was lower at the Fe-Al side comparing with weld seam and steel substrate, which led to a preferentially diffusion of Si to the Fe/Al interface and finally caused the aggregation of Si in the Fe/Al interface. Si addition improved the joint strength and reduced the required laser power for a suitable joint. The joint produced with the AlSi5 filler metal had the highest tensile strength and largest fracture displacement.