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Effect of beam wobbling on laser welding of aluminum and magnesium alloy with nickel interlayer
摘要： The influence of conventional laser keyhole welding and beam wobbling was evaluated at two weld travel speeds and power settings. Fracture in linear lap welds would occur during specimen preparation due to the presence of Al-rich brittle fusion zone, unless one utilizes a circular laser wobbling path (at 1000 Hz). Wobbling provided better integrity due to the presence of a Mg-rich ductile fusion zone and a larger bonded width. It can be concluded that laser beam wobbling enhances joint quality by widening the joint area and mitigating formation of brittle secondary phases at the joint fusion zone.
关键词： Aluminum,Magnesium,Interlayer,Laser welding,Beam wobbling,Microstructure
更新于2025-11-28 14:24:20
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Mechanism study on the effects of power modulation on energy coupling efficiency in infrared laser welding of highly-reflective materials
摘要： High-reflectivity of materials, such as magnesium, copper and aluminum, results in low thermal efficiency of their infrared laser welding processes. AZ31 magnesium alloy was selected to study the effects of power modulation on energy coupling efficiency in laser welding of highly-reflective materials. A model for the relationship between energy coupling efficiency and modulation parameters was obtained. The energy coupling efficiency in optimized modulated-power laser welding was about 1.58 times that in constant-power welding. The mechanism was explored by analyzing keyhole evolution and the resulted pressure distribution along keyhole wall during welding. The keyhole evolutions in laser continuous welding of common material (Q345 steel, reflectivity of 65%) and highly-reflective material (AZ31, reflectivity of 85%) were observed through high-speed imaging by utilizing a half sandwich method. The results indicated that the secret of improving energy coupling efficiency of laser welding process of highly-reflective materials through power modulation was the formation of a deep keyhole and its long life. When instantaneous power decreased from the peak, there was still enough recoil pressure at the bottom of keyhole to resist surface tension and hydrostatic pressure of liquid metal, which was the fundamental reason for the long time existence of keyhole with a large depth.
关键词： laser welding,magnesium alloy,recoil pressure,keyhole,highly-reflective materials,power modulation
更新于2025-11-28 14:24:20
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Laser welding of AZ31B magnesium alloy with beam oscillation
摘要： Circular beam oscillation was introduced to laser welding of 2 mm-thick AZ31 magnesium alloy. The appearance, microstructure and tensile properties of the welds were investigated. It was found that the low frequency about 50 Hz and the small radius about 0.5 mm are more beneficial to improve the weld appearance, under the given parameters of laser power 2 kW, welding speed 2 m/min and beam oscillating diameter 0.35 mm. The undercut defect and even the totally collapse of the weld appear when employing the frequency higher than 75 Hz or the radius larger than 1.5 mm. The microstructure evolution mainly reflects in the variation of the proportions of the equiaxed zone (PEZ) and the average grain size (SG). The PEZ decreases from 85% to 42% with the beam oscillating frequency increasing from 25 Hz to 100 Hz, while the SG reaches the maximum of 37.5 μm at 75 Hz. The PEZ decreases and the SG increases with the increase of beam oscillating radius. The results showed that the tensile strength and elongation are closely related to the PEZ, the SG and the twins. According to the experimental results, the relationship of oscillating parameters, microstructure, and tensile properties was established.
关键词： Laser oscillating welding,Magnesium alloy,Microstructure,Tensile properties
更新于2025-11-28 14:24:20
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Microstructural Characteristics of Laser Metal Deposited Magnesium Alloy AZ31
摘要： Up to now, only a limited amount of metallic materials is investigated for laser additive manufacturing (LAM). However, the demand to widen the application possibilities by enlarging the range of materials for LAM is growing fast. By now, titanium and aluminium alloys are in the focus of research. In contrast, magnesium alloys are rarely used in the field of additive manufacturing, although they possess a low density in combination with a high specific strength. Currently, magnesium structures are mainly produced by casting but during the last years, the use of wrought alloys also increased. A reason for the rare use of magnesium alloys for LAM technologies might be the high flammability of magnesium powders. This difficulty can be avoided by using magnesium wire for laser metal deposition (LMD). In the present study, the microstructural characteristics of a LMD processed AZ31 magnesium alloy are investigated. For this purpose, optical microscopy and scanning electron microscopy were used. With the help of EDX and EBSD analysis, a change of the chemical composition and micro texture with structure height was identified. The relationship of microstructure and local mechanical properties was investigated with the help of Vickers micro hardness testing. Based on the obtained results it can be concluded that the microstructural characteristics of laser additive manufactured magnesium alloys differ from those of titanium and aluminium alloys. Thus, a wider application spectrum of LMD and magnesium alloys can be opened up.
关键词： laser metal deposition,local mechanical properties,microstructure,magnesium alloy,wire,microtexture
更新于2025-11-28 14:24:20
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Wear and Corrosion Resistance of Al0.5CoCrCuFeNi High-Entropy Alloy Coating Deposited on AZ91D Magnesium Alloy by Laser Cladding
摘要： In order to improve the wear and corrosion resistance of an AZ91D magnesium alloy substrate, an Al0.5CoCrCuFeNi high-entropy alloy coating was successfully prepared on an AZ91D magnesium alloy surface by laser cladding using mixed elemental powders. Optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction were used to characterize the microstructure of the coating. The wear resistance and corrosion resistance of the coating were evaluated by dry sliding wear and potentiodynamic polarization curve test methods, respectively. The results show that the coating was composed of a simple FCC solid solution phase with a microhardness about 3.7 times higher than that of the AZ91D matrix and even higher than that of the same high-entropy alloy prepared by an arc melting method. The coating had better wear resistance than the AZ91D matrix, and the wear rate was about 2.5 times lower than that of the AZ91D matrix. Moreover, the main wear mechanisms of the coating and the AZ91D matrix were different. The former was abrasive wear and the latter was adhesive wear. The corrosion resistance of the coating was also better than that of the AZ91D matrix because the corrosion potential of the former was more positive and the corrosion current was smaller.
关键词： laser cladding,wear,AZ91D magnesium alloy,high-entropy alloy coating,corrosion
更新于2025-11-21 11:24:58
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Laser additive manufacturing of biodegradable magnesium alloy WE43: a detailed microstructure analysis
摘要： WE43, a magnesium alloy containing yttrium and neodymium as main alloying elements, has become a well-established bioresorbable implant material. Implants made of WE43 are often fabricated by powder extrusion and subsequent machining, but for more complex geometries laser powder bed fusion (LPBF) appears to be a promising alternative. However, the extremely high cooling rates and subsequent heat treatment after solidification of the melt pool involved in this process induce a drastic change in microstructure, which governs mechanical properties and degradation behaviour in a way that is still unclear. In this study we investigated the changes in the microstructure of WE43 induced by LPBF in comparison to that of cast WE43. We did this mainly by electron microscopy imaging, and chemical mapping based on energy-dispersive X-ray spectroscopy in conjunction with electron diffraction for the identification of the various phases. We identified different types of microstructure: an equiaxed grain zone in the center of the laser-induced melt pool, and a lamellar zone and a partially melted zone at its border. The lamellar zone presents dendritic lamellae lying on the Mg basal plane and separated by aligned Nd-rich nanometric intermetallic phases. They appear as globular particles made of Mg3Nd and as platelets made of Mg41Nd5 occurring on Mg prismatic planes. Yttrium is found in solid solution and in oxide particles stemming from the powder particles’ shell. Due to the heat influence on the lamellar zone during subsequent laser passes, a strong texture developed in the bulk material after substantial grain growth.
关键词： Rapid solidification,Microstructure,Bone scaffolds,Electron microscopy,Biodegradable implants,WE43,Laser powder bed fusion,Magnesium
更新于2025-11-21 11:20:48
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Magnesium tetrapyrazinoporphyrazines: tuning of the pKa of red-fluorescent pH indicators
摘要： Magnesium (II) tetrapyrazinoporphyrazines (TPyzPzs) are excellent red fluorophores (λF ~ 663 nm, ΦF ~ 0.53 in THF). In this work, a series of magnesium (II) complexes of unsymmetrical TPyzPzs bearing one or two phenol substituents was prepared. Suitable substitutions on the phenolic moiety tuned its pKa in the range of 5.5 to 13. Deprotonation of the phenolic group at higher pH induced a strong donor (phenolate) in the macrocycle that led to pH-dependent quenching of the red fluorescence of these indicators. pH sensing was proven in water solutions after incorporation of TPyzPs into two delivery systems – microemulsions and liposomes. The latter also serves as a simple model of biomembranes. Finally, a wavelength-ratiometric probe was constructed by incorporation of a TPyzPz indicator and lipophilic pH-nonsensitive BODIPY dye into liposomes. Synthetic precursors for TPyzPzs, substituted pyrazine-2,3-dicarbonitriles, also represent donor-acceptor system and the pH-dependent changes in absorption spectra may be easily visible to the naked eye.
关键词： pH indicators,microemulsions,fluorescence,BODIPY,wavelength-ratiometric probe,liposomes,tetrapyrazinoporphyrazines,magnesium complexes
更新于2025-11-20 15:33:11
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Photocatalytic CO2 reduction on porous TiO2 synergistically promoted by atomic layer deposited MgO overcoating and photodeposited silver nanoparticles
摘要： In this work, a porous TiO2 photocatalyst derived from metal-organic framework MIL-125 was synthesized and tested for photocatalytic CO2 reduction with water. To improve the photocatalytic performance, innovative materials modifications were employed by decorating TiO2 with atomic layer deposited (ALD) MgO overcoating and photodeposited silver (Ag) nanoparticles at different orders: MgO deposition followed by Ag (i.e. Ag/MgO/TiO2), or Ag deposition followed by MgO (i.e. MgO/Ag/TiO2). The addition of Ag promoted transfer of photoinduced electrons, while the coating of an ultrathin MgO layer inhibited surface charge recombination and enhanced CO2 adsorption. The combination of MgO and Ag resulted in synergistic promotion on CO2 photoreduction greater than the sum of individual promotional effects. The Ag/MgO/TiO2 catalyst with 7 ALD-layers of MgO and 5% Ag was 14 times more active than the pristine TiO2 in terms of CO and CH4 production. In addition, the sequence of MgO/Ag decoration influenced the catalytic activity. The Ag/MgO/TiO2 catalysts were in general more active than the MgO/Ag/TiO2 counterparts, likely due to the different electron mobility and Ag nanoparticle distribution on the surface. This work for the first time reports the novel materials structure of ALD coated MgO and photodeposited Ag nanoparticles on TiO2, and it reveals the importance of optimizing materials morphology and structure to promote the catalytic activity.
关键词： CO2 photoreduction,magnesium oxide,silver nanoparticles,atomic layer deposition,porous TiO2
更新于2025-11-14 17:03:37
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Excellent catalysis of TiO2 nanosheets with high-surface-energy {001} facets on hydrogen storage properties of MgH2
摘要： Transition metal compound is one of the highly efficient catalysts in improving the reaction kinetics of hydrogen storage materials. Among all the transition metal, titanium and its compounds show great catalytic effect on magnesium hydride. In this paper, TiO2 nanosheets with exposed {001} facets were synthesized and doped into MgH2 for the first time. The TiO2 nanosheets (NS) doped MgH2 shows superior kinetic performance and lowest desorption temperature. The onset temperature of MgH2 + 5 wt% TiO2 NS to release hydrogen is 180.5 °C and the corresponding peak temperature is 220.4 °C, which are greatly lower than those of pure MgH2 and also distinctly lower than those of MgH2 + 5 wt% TiO2 nanoparticles (NP). For isothermal dehydrogenation analysis, the MgH2 + 5 wt% TiO2 NS can release 6.0 wt% hydrogen within 3.2 min at 260 °C and desorb 5.8 wt % hydrogen within 6 min at 240 °C. It is worth noting that the MgH2 + 5 wt% TiO2 NS can even release 1.2 wt% hydrogen at a temperature as low as 180 °C within 300 min. The hydrogenation kinetics of MgH2 + 5 wt% TiO2 NS is also greatly improved, which could absorb hydrogen within only a few seconds at the mild temperature. It can uptake 3.3 wt% hydrogen at 50 °C and 5.4 wt% at 100 °C within 10 s. It is demonstrated that the tremendous enhancement in reaction kinetics of MgH2 can be ascribed to the nanometer size and highly active {001} facets of anatase TiO2. The higher average surface energy can significantly reduce the hydrogen desorption activation energy of MgH2 to 67.6 kJ/mol, thus easily improves the hydrogen desorption properties.
关键词： Magnesium hydride,Hydrogen storage,Catalytic effects,crystal facets,TiO2
更新于2025-11-14 17:03:37
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Color-center formation and thermal recovery in X-ray and electron-irradiated magnesium aluminate spinel
摘要： We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 10^18 cm^?2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VO^x) and singly ionized (VO^.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers.
关键词： thermal recovery,X-ray irradiation,color centers,threshold displacement energy,F centers,electron irradiation,absorption spectroscopy,magnesium aluminate spinel
更新于2025-09-23 15:23:52