Broad-beam laser cladding of Al-Cu alloy coating on AZ91HP magnesium alloy

The resistance to wear and corrosion of AZ91HP Mg alloy was improved by laser cladding Al-Cu alloy. It was found that the clad layer was characterized by AlCu₄ and Mg₁₇Al₁₂ grains embedded in a AlMg matrix. The bonding zone exhibited a white-light planar crystal band with thickness of 10-13 μm. The heat-affected zone formed a eutectic structure due to the Mg diffusion. The microhardness and wear resistance of the coating were improved due to the formation of the hard phases AlCu₄ and Mg₁₇Al₁₂. Owing to the formation of dense Al₂O₃ oxide film, the coating exhibited better corrosion resistance in 3.5 wt.% NaCl solution.     

Composition design and laser cladding of Ni-Zr-Al alloy coating on the magnesium surface

The cluster line criterion was used for optimized design of a Ni-Zr-Al alloy used as coating on the AZ91HP magnesium alloy by laser cladding. Results show that the coating mainly consists of an amorphous, two ternary intermetallic phases with Ni₁₀Zr₇ and Ni₂₁Zr₈ type structures resulting in high hardness, good wear resistance and corrosion resistance. The interface between the clad layer and the substrate has good metallurgical bond.     

钛合金表面激光熔覆TiC_p/Ni基合金复合耐磨涂层

采用激光熔覆技术在TC4合金表面制备TiC颗粒增强的Ni基合金复合材料涂层,测试了熔覆层的硬度和滑动摩擦磨损性能,分析了熔覆层的强化机制。结果表明,熔覆层中存在颗粒强化、固溶强化和细晶强化等多种强化作用,熔覆层的显微硬度达HV900～1100,耐磨性能比TC4合金显著提高。     

激光熔覆Al+SiC涂层对镁合金表面耐磨性能的改性

通过脉冲激光器(Nd-YAG)在AZ91D镁合金基底上熔覆Al+SiC粉体。采用扫描电子显微镜、能量色散谱（EDS）和X-射线衍射测定分析熔覆层的显微组织、化学成分和物相组成。研究表明：Al+SiC涂层主要由SiC,b-Mg17Al12及Mg和Al相组成,激光熔覆层与镁合金基底表现出良好的冶金结合。所有样品都具有树枝状结构,且随着SiC质量分数的增大,树枝状和胞状结构的间隔变得更大。熔覆涂层的表面硬度高于基底,并且随着熔覆层中的SiC质量分数的增加而增大,SiC质量分数为40%的熔覆层具有最大的显微硬度,达到180 HV,然而质量分数为10%的熔覆层硬度为136 HV。销盘滑动磨损试验表明,复合涂层中的SiC颗粒和原位合成的Mg17Al12相显著提高了AZ91D镁合金的耐磨损性,其中,SiC质量分数从10%增加到30%过程中磨损体积损失逐渐减少,SiC质量分数在20%～30%时熔覆层具有最好的耐磨性。     

激光熔覆Al+SiC涂层对镁合金表面耐磨性能的改性

通过脉冲激光器(Nd-YAG)在AZ91D镁合金基底上熔覆Al+SiC粉体。采用扫描电子显微镜、能量色散谱(EDS)和X-射线衍射测定分析熔覆层的显微组织、化学成分和物相组成。研究表明:Al+SiC涂层主要由SiC,β-Mg_(17)Al_(12)及Mg和Al相组成,激光熔覆层与镁合金基底表现出良好的冶金结合。所有样品都具有树枝状结构,且随着SiC质量分数的增大,树枝状和胞状结构的间隔变得更大。熔覆涂层的表面硬度高于基底,并且随着熔覆层中的SiC质量分数的增加而增大,SiC质量分数为40%的熔覆层具有最大的显微硬度,达到180 HV,然而质量分数为10%的熔覆层硬度为136 HV。销盘滑动磨损试验表明,复合涂层中的SiC颗粒和原位合成的Mg_(17)Al_(12)相显著提高了AZ91D镁合金的耐磨损性,其中,SiC质量分数从10%增加到30%过程中磨损体积损失逐渐减少,SiC质量分数在20%~30%时熔覆层具有最好的耐磨性。     

Microstructure and properties of 6FeNiCoSiCrAlTi high-entropy alloy coating prepared by laser cladding

The content of each constituent element in the newly developed high-entropy alloys (HEAs) is always restricted in equimolar or near-equimolar ratio in order to avoid the formation of complex brittle phases during the solidification process. In this study, a 6FeNiCoSiCrAlTi high-entropy alloy coating with simple BCC solid solution phase has been prepared by laser cladding on a low carbon steel substrate. The microstructure, hardness and magnetic properties have been investigated. The experimental results show that the tendency of component segregation in the conventional solidification microstructure of multi-component alloy is effectively relieved. The microstructure of the coating is mainly composed of equiaxed polygonal grains, discontinuous interdendritic segregation and nano-precipitates. EBSD observation confirms that the polygonal grains and interdendritic segregation have similar BCC structure with lots of low angle grain boundaries at the interface. The microhardness of the coating reaches 780 HV_0.5, which is much higher than most of the HEAs prepared by other methods. In addition, the coating shows excellent soft magnetic properties.     

Laser (a pulsed Nd:YAG) cladding of AZ91D magnesium alloy with Al and Al2O3 powders

The laser surface cladding of an AZ91D magnesium alloy with Al and Al₂O₃ powders was investigated using a pulsed Nd:YAG laser. The optimum ratio of Al to Al₂O₃ and the suitable range of laser processing parameters were identified. The resulting microstructure in the modified surface layer was examined and the wear resistance property was evaluated. The results show that the wear resistance of the laser treated samples was much superior to that of the untreated samples.     

Enhanced microwave absorption of Fe flakes with magnesium ferrite cladding

Surface cladding of Magnesium ferrite (MgFe₂O₄) was found to be helpful for effectively decreasing the permittivity of Fe flakes. So the electromagnetic impedance matching was improved, resulting in a good microwave absorption. Careful characterizations showed that the giant decreases of permittivity were ascribed to the high resistivity of surface due to the MgFe₂O₄ cladding. A high frequency microwave absorption property with thin absorber thickness was obtained for the Fe flakes with 10 wt% MgFe₂O₄.     

Mg-Sn-Si系合金的热力学基础及合金相演变过程分析

研究了Mg-Sn-Si系合金的热力学基础及合金相的演变过程. 结果表明: 对于Mg-Sn-Si系合金, 合金相的比热容随着温度增加而增加, 在低温下变化迅速, 而在高温下变化平缓, 其热膨胀系数在低温范围内随温度升高呈指数形式增加, 而在高温范围内呈线性增大. 在Mg₂ (Si_x, Sn_1-x)、Mg₂ (Sn_x, Si_1-x)相结构中, Sn(Si)原子的取代位置不固定, 可以是面心, 也可以是顶点. 常规凝固过程中, 由于处于非平衡状态, x的取值范围有所波动, 对于Mg₂ (Si_x, Sn_1-x)和Mg₂ (Sn_x, Si_1-x) 两种结构, x的取值范围在0.25或0.75附近. Mg₂ (Si, Sn)的生成温度较高, 可从液相中直接析出, 也可由Mg₂Si转化而来, 而Mg₂ (Sn, Si)的生成温度较低, 只能从基体中析出, 随着Sn含量的增加, 开始析出Mg₂ (Sn, Si)相的温度升高.     

Laser glazing of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaalumminate (LMA) is an important candidate for thermal barrier coatings due to its thermal stability and low thermal conductivity. On the other hand, laser glazing method can potentially make thermal barrier coatings impermeable, resistant to corrosion on the surface and porous at bulk. LMA powder was synthesized at 1600 °C by solid-state reaction, pressed into tablet and laser glazed with a 5-kW continuous wave CO₂ laser. Dendritic structures were observed on the surface of the laser-glazed specimen. The thicker the tablet, the easier the sample cracks. Cracking during laser glazing is attributed to the low thermal expansion coefficient and large thickness of the sample.     

Electrodeposition of Al-Mn alloy on AZ31B magnesium alloy in molten salts

The Al-Mn alloy coatings were electrodeposited on AZ31B Mg alloy in AlCl₃-NaCl-KCl-MnCl₂ molten salts at 170 °C aiming to improve the corrosion resistance. However, in order to prevent AZ31B Mg alloy from corrosion during electrodeposition in molten salts and to ensure excellent adhesion of coatings to the substrate, AZ31B Mg alloy should be pre-plated with a thin zinc layer as intermediate layer. Then the microstructure, composition and phase constituents of the coatings were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). It was indicated that, by adjusting the MnCl₂ content in the molten salts from 0.5 wt% to 2 wt%, the Mn content in the alloy coating was increased and the phase constituents were changed from f.c.c Al-Mn solid solution to amorphous phase. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. It was confirmed that the Al-Mn alloy coatings exhibited good corrosion resistance with a chear passive region and significantly reduced corrosion current density at anodic potentiodynamic polarization. The corrosion resistance of the alloy coatings was also related with the microstructure and Mn content of the coatings.     

Corrosion resistant properties of polyaniline-acrylic coating on magnesium alloy

The performance of the paint coating based on acrylic-polyaniline on magnesium alloy ZM 21 has been studied by electrochemical impedance spectroscopy in 0.5% NaCl solution. The polyaniline was prepared by chemical oxidative method of aniline with ammonium persulphate in phosphoric acid medium. The phosphate-doped polyaniline was characterized by FTIR and XRD methods. Acrylic paint containing the phosphate-doped polyaniline was prepared and coated on magnesium ZM 21 alloy. The coating was able to protect the magnesium alloy and no base metal dissolution was noted even after 75 days exposure to sodium chloride solution.     

Self-assembled monolayers on magnesium alloy surfaces from carboxylate ions

Self-assembled monolayers (SAMs) of carboxylate salts (C_n−1H_2n−1COONa, n = 12, 16, 18) were successfully formed on Mg alloy substrate in ethanol solution and characterized by the contact angle measurement, ATR-FTIR, ellipsometry and XPS. The SAMs were regularly and densely anchored to the Mg alloy substrate via monodentate bonding with the tilting angles of about 40°, 33° and 27° for C12, C16 and C18 monolayers, respectively. Electrochemical impedance spectroscopy (EIS) proved the corrosion protection of SAMs for Mg alloy substrate with protective efficiency (PE) of even up to 98.5%.     

Preparation and properties of super-hydrophobic coating on magnesium alloy

The super-hydrophobic coating was successfully fabricated on the surface of magnesium alloy AZ31 by chemical etching and surface modification. The surface morphologies, compositions, wettability and corrosion resistance of the coating were investigated with SEM, XPS, contact angle measurement and electrochemical method, respectively. It shows that the rough and porous micro-nano-structure was presented on the surface of magnesium alloy, and the contact angle could reach up to 157.3 ± 0.5° with sliding angle smaller than 10°. The super-hydrophobic coating showed a long service life. The results of electrochemical measurements showed that anticorrosion property of magnesium alloy was improved. The super-hydrophobic phenomenon of the prepared surface was analyzed with Cassie theory, and it finds that only about 10% of the water surface is contacted with the metal substrate and the rest 90% is contacted with the air cushion.     

Laser formed amorphous Fe-based alloy

the amorphous layers were obtained using the method of CW CO_2 laser scanning Fe-based alloy surface. The function of structure of Fe-based alloy, scanning speed, cooling method etc. for laser-formed amorphous state were discussed. A much thick amorphous layer can be made by laser scanning.     

Microstructure and wear resistance of laser clad cobalt-based alloy multi-layer coatings

Multi-layer Co-based alloy (HMSP 2537) were deposited on Ni-based superalloy plate with a TJ-TL-T5000 type CO₂ laser. Sections of such coatings were examined to reveal their microstructure and phase composition using optical microscope, scanning electron microscope (SEM), and X-ray diffractometer (XRD). The hardness and wear resistance of the coatings were tested. The results showed that the prime phase (γ-Co dendrite) and other phases, such as CrNi, Co₇W₆, and Cr₂₃C₆ existed in the coatings. Dendrite or cellular microstructures were observed perpendicular to the interface, and coarsening microstructures were obtained as more layers deposited. Dendrite paralleling to laser scan speed was also found near the top surface of the last layer. Fine microstructures of γ-Co dendrite and lamellar eutectic in inter-dendritic regions strengthened the coatings. Microhardness and wear resistance of the coatings were much higher than that of substrate but slightly decreased with layers increased.     

Laser induced damage of multi-layer dielectric used in pulse compressor gratings

Laser induced damage threshold (LIDT) of multi-layer dielectric used in pulse compressor gratings (PCG) was investigated. The sample was prepared by e-beam evaporation (EBE). LIDT was detected following ISO standard 11254-1.2. It was found that LIDTs of normal and 51.2°incidence (transverse electric (TE) mode) were 14.14 and 9.31 J/cm2, respectively. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was pit-concave-plat structure for normal incidence, while it was pit structure for 51.2°incidence with TE mode. The electric field distribution was calculated to illuminate the difference of LIDT between the two incident cases.     

Laser induced damage of multi-layer dielectric used in pulse compressor gratings

Laser induced damage threshold (LIDT) of multi-layer dielectric used in pulse compressor gratings (PCG) was investigated. The sample was prepared by e-beam evaporation (EBE). LIDT was detected following ISO standard 11254-1.2. It was found that LIDTs of normal and 51.2°incidence (transverse electric (TE) mode) were 14.14 and 9.31 J/cm2, respectively. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was pit-concave-plat structure for normal incidence, while it was pit structure for 51.2°incidence with TE mode. The electric field distribution was calculated to illuminate the difference of LIDT between the two incident cases.     

静磁场对镁合金凝固组织的影响

镁合金是一种具有发展潜力的轻合金材料，但尚有待进一步的研究.通过实验研究静磁场作用下镁合金AZ61的凝固过程及其组织，发现在施加静磁场后镁合金的组织发生明显变化，晶界减薄，溶质元素含量在晶内显著增加，而在晶界处略有下降，因此静磁场改善了镁合金的组织，对提高镁合金的性能有重要意义. 关键词： 镁合金 静磁场 溶质元素     

Characteristics of cobalt-based alloy coating on tool steel prepared by powder feeding laser cladding

Co-based alloy coating was deposited on tool steel by powder feeding laser cladding. Sections of such coatings were examined to reveal their microstructures and phases using scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results showed that the prime phase (γ-Co dendrite) and other phases, including Cr₂₃C₆, Co₇W₆, and CrNi existed in the coatings. Some different solidification morphologies, such as planar (at the interface), cellular and dendrite formed, varying from the interface to the surface. Fine microstructures of γ-Co dendrite and lamellar eutectic in dendritical regions strengthened the coatings. Besides, the effects of aged treatment on the microstructure and microhardness of the surface coating were studied. Aged treatment led to the precipitations of some carbide particles (Cr₇C₃ and Co₃C) and boride particles (Co₄B) from the cladded coating, causing an increase in microhardness in the laser-cladded coating.