Stress Corrosion Behavior of AM50Gd Magnesium Alloy in Different Environments

A new type of high strength corrosion-resistant magnesium alloy was prepared by adding 1% rare earth Gd to AM50 and then treated with hot extrusion method. The stress corrosion properties of the new materials in air, pure water, 0.5 mol/L NaCl, and 0.5 mol/L Na2SO4 solution were studied by the slow strain rate tensile (SSRT) test, in situ open circuit potential test, Tafel curve test, stereomicroscope, SEM, and EDS. The results showed the following. The stress corrosion sensitivity of the material in different environments was Na2SO4 > NaCl > distilled water > air. According to the Tafel curves measured at 0 and 100 MPa, the corrosion voltage decreased little and the corrosion current density increased rapidly under 100 Pa. This was because the film of the corrosion product ruptured to form a large cathode and a small anode, which resulted in a large instantaneous corrosion current. The mechanism of hydrogen embrittlement and anodic dissolution together affected the stress corrosion behavior of the alloy. In distilled water, hydrogen embrittlement played a major role, while in NaCl and Na2SO4 solution, hydrogen embrittlement and anodic dissolution were both affected. The direct reason of the stress corrosion crack (SCC) samples’ failure was the cracks expanding rapidly at the bottom of pit, which was caused by corrosion

Optimizing the Mechanical Properties in the Repair Zone of 5Cr5MoV by Controlling Welding Heat Input

The influence of welding heat input on the microstructure and mechanical properties of 5Cr5MoV die steel was studied in order to improve the mechanical properties of the cold working die and extend its service life. Shielded metal arc welding (SMAW) method was used with different heat inputs in the range from 4.2 to 6.61 kJ/cm to repair the 5Cr5MoV die steel. Microhardness and tensile properties were performed to evaluate the repaired quality of the cold working die steel. The microhardness of the weld repaired zone gradually decreased from the weld to the tempering zone. The highest microhardness in the weld repaired zone was 863 HV, and finally, it decreased to about 300 HV. With the increase of heat input, the tensile strength of the weld and the heat affected zone increased; nevertheless, the tensile strength of the tempering zone increased first and then decreased. As a result, 6.6 kJ/cm is the best value of heat input judged from the microhardness distribution and the tensile properties

A Large Mode Area Parabolic-Profile Core Fiber with Modified Segmented in Cladding

In this paper, a novel fiber with a parabolic-profile core and eight segmented trenches in cladding is designed. The designed fiber consists of the segmented trench of low refractive index in cladding and parabolic-profile of high refractive index in the core. The proposed fiber has good bending resistance. The eight segmented trenches in the cladding can decrease the refractive index of cladding to increase the difference index between the core and cladding to limit fundamental mode (FM) loss. The proposed fiber can offer an effective single mode (SM) operation with a large mode area (LMA) of 952 µm2 at the small bending radius (R = 10 cm). In addition, the fiber is also suitable under an 18 W/m heat load. The proposed fiber achieves good bending performance, which can be suitable for the compact high-power lasers

Regular Fe3O4 octahedrons with excellent soft magnetic properties prepared by dealloying technique

The dealloying processes of Al-15Fe (at.%) alloy ribbons consisting of two distinct phases of α-Al (Fe) and AlFe in NaOH solutions were investigated. The effects of NaOH solution concentration, dealloying temperature and time on the results were comparatively discussed. The as-dealloyed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). It was found that all of the three experimental conditions could affect the morphology of the as-dealloyed samples, and the influence of solution concentration was the crucial factor. The Al could be leached out from both the α-Al (Fe) and AlFe phases to obtain regular octahedral FeO under most of the experimental conditions except for that in the 0.5 mol L NaOH solution at ambient temperature. In particular, the FeO from dealloying Al-15Fe ribbons in 5 mol L NaOH solution for 48 h at ambient temperature shows a uniform octahedral structure (average edge length: 667 ± 158 nm) and special magnetic properties (saturation magnetization: 83.3 emu g, residual magnetization: 10.4 emu g and coercive force: 256.9 Oe), implying its potential applications in magnetic fluid, information storage, etc

Effect of Adding Rare Earth Elements Er and Gd on the Corrosion Residual Strength of Magnesium Alloy

The effects of the single and compound addition of rare earth Gd and Er on corrosion resistance and residual strength of as-cast AM50 magnesium alloy were studied using XRD, SEM, EDS, the weightlessness test, electrochemistry method, and tensile test. The results of XRD and SEM showed that Al3Er, Al2Gd3, and Al–Mn–Gd(Er) phases appeared in the alloy structure after the addition of rare earth Er and Gd. The results from the weightlessness test and Tafel curves show that the corrosion resistance of the modified composite rare earth was improved. Stress concentration caused by a corrosion pit is the direct cause of the tensile samples after corrosion. The corrosion residual strength of modified composite rare earth specimens is better than that of modified single rare earth samples. Fracture analysis indicates that the addition of rare earth elements did not change the fracture mechanism of the alloy, and the fracture was still the cleavage fracture

Microstructure and Mechanical Properties of Friction Stir-Welded Dissimilar Joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn Alloys

In order to clarify the microstructural evolution and the mechanical property of dissimilar friction stir-welded joints of ZK60 and Mg-4.6Al-1.2Sn-0.7Zn magnesium alloys, two types of arrangement with ZK60 at advancing side (AS) or retreating side (RS) were adopted. The macrostructure and the microstructure of the dissimilar welded joints were discussed, and the microhardness and the transverse tensile properties of the joints were measured. There are three stirring sub-zones with different compositions and two clear interfaces within the joints. Due to the effect of both the original grain size of base materials and the growth of recrystallized grains, in the stir zone (SZ), the grain size of ZK60 increased slightly, while the grain size of Mg-4.6Al-1.2Sn-0.7Zn decreased significantly. The dissolution of precipitates was gradually significant from RS to AS within the SZ due to the gradual increase in strain and heat. The grain refinement led to an increase in hardness, while the dissolution of precipitates resulted in a decrease in hardness. The performance of the joints obtained with ZK60 placed on the RS is slightly better than that of that on the AS. The tensile fracture of both joints occurred at the interface between SZ and the thermos-mechanical affected zone at the AS, and showed a quasi-dissociative fracture

Kinetics of the austenitization in the Fe-Mo-C ternary alloys during continuous heating

The influence of molybdenum on the microstructure and kinetics of the austenization of the Fe-Mo-C ternary alloys is analyzed using differential scanning calorimetry (DSC) and the Johnson-Mehl-Avrami-Kolmogorov model (JMAK) in the temperature range from 293 K to 1373 K. The as-cast microstructure and microstructure after DSC test are obtained using optical microscopy (OM) and scanning electron microscopy (SEM). It was seen that with an increasing Mo concentration, the lamellar pearlite is spherized and the austenite grain size decreases. In addition, both DSC curves and the JMAK model show that the initial (Ac1) and the final (Ac3) temperature of the phase transition increases with an increasing Mo concentration. It was also seen that increasing the Mo concentration, the diffusion activation energy (DAE) increases and the pre-exponential factor of diffusion (DPEF) decreases due to a change in both the austenitic nucleation rate and the diffusion of the elements caused by the introduction of Mo

Genome-Wide Identification of MYB Transcription Factors and Their Function on Floral Volatile Compounds Biosynthesis in <i>Antirrhinum majus</i> L.

The v-MYB avivan myoblastsis virus oncogene homolog (MYB) family is the largest gene family of the transcription factor in plants, involved in plant growth and development, secondary metabolism and resistance to biotic/abiotic stress. Antirrhinum majus (snapdragon) is an ideal material for studying ornamental traits. Nevertheless, there has been no systematic investigation into the AmMYB family of snapdragons. In this study, we identified a total of 162 members of the AmMYB gene family in snapdragons. Gene structure analysis showed that the AmMYB family within the same subgroup had a similar structure and motifs. Analysis of gene duplication events revealed that the amplification of the AmMYB family was driven by whole-genome duplication (WGD) and dispersed duplication. The analysis of cis-acting elements in the promoter region of AmMYB genes reveals a collaborative involvement of light-responsive growth and development elements, stress resistance elements, and hormone-responsive elements jointly participating in the regulation of the AmMYB gene. Collinearity analysis demonstrates significant functional distinctions between AmMYB and monocotyledonous plants. The classification of AmMYB members results in 3 main subgroups with 36 smaller subgroups. All AmMYB genes are distributed across all eight chromosomes, with no apparent correlation between subfamily distribution and chromosome length. Through phylogenetic analysis and RNA-seq analysis, we have identified 9 R2R3-MYB genes that potentially play a role in the regulation of floral volatile organic compounds (FVOCs) biosynthesis. Their expression patterns were verified by qRT-PCR experiments. This study establishes a robust foundation for further investigations into the functionality of AmMYB genes and their molecular mechanisms underlying FVOC biosynthesis in snapdragons

Magnetic Hydroxyapatite-Coated Iron–Chromium Microspheres for Dental Surface Polishing and Plaque Removal

This research aimed to engineer magnetic hydroxyapatite-coated iron–chromium (HAp–FeCr) microspheres to enhance dental surface polishing and plaque elimination. Utilizing a tailored sol–gel approach, the HAp–FeCr microspheres were synthesized and exhaustively characterized via scanning electron microscopy, energy-dispersive X-ray spectroscopy, ζ-potential, X-ray diffractometry, and X-ray photoelectron spectroscopy methodologies. Key findings showcased that these microspheres retained their magnetic properties post-HAp coating, as evidenced by the magnetization curves. An innovative magnetic polishing system was developed, incorporating these microspheres and a 2000 rpm magnet. Comparative evaluations between traditional air-powder polishing and the proposed magnetic technique demonstrated the latter’s superiority. Notably, the magnetic polishing led to a substantial reduction in dental plaque on the tooth surface, decreasing bacterial adhesion and early biofilm formation by Streptococcus gordonii and Lactobacillus acidophilus, where the most pronounced effects were observed in samples with elevated HAp content. A significant 60% reduction in dental plaque was achieved with the magnetic method relative to air-powder polishing. Furthermore, the HAp–FeCr microspheres’ biocompatibility was verified through cytotoxicity tests and animal studies. In essence, the magnetic HAp–FeCr microspheres present a novel and efficient strategy for dental treatments, holding immense potential for improving oral health