关键词： magnesium alloys   rare-earth metals   solid solution decomposition   aging-induced recovery   mechanical properties  

摘要： The recovery (softening) in magnesium alloys with gadolinium (yttrium group REM) and in these alloys additionally alloyed with samarium (cerium group REM) is studied after age hardening and subsequent short-term annealing performed at a slightly higher temperature. The aging-induced hardening is found to decrease at a high annealing temperature, at which the recovery occurs. The recovery of the magnesium-gadolinium alloys decreases with increasing samarium content in them. Small samarium additives are shown to increase the strength properties and, simultaneously, to decrease the recovery of the Mg-Gd alloys during accidental short-term heating when the alloys are used as lightweight structural materials in practice.

关键词： soundness   shrinkage porosity   pinhole porosity leak   thin-walled castings   magnesium casting   alloys ML10   Elektron 21   EZ33A   ZE41A   ZE63A  

摘要： The production of various housings of the units operating under the pressure of liquids or gases requires the use of alloys with increased soundness after casting. We compare the properties of the magnesium alloys most widely used for producing leakproof castings, namely, ML10, Elektron 21, EZ33A, ZE41A, and ZE63A. For each of them, the equilibrium and nonequilibrium freezing ranges, the heat of solidification, and the fraction of eutectic in a structure are calculated, and the dynamics of the change in the rate of solidification of an alloy in the freezing range is estimated. The shape and size of shrinkage cavity in castings made of the alloys are also determined, and the shrinkage porosity of the castings was measured. The causes for the low soundness of the ML10 alloy castings are considered. The contribution of the eutectic phase content and the freezing range wideness of an alloy to the formation of a soundness casting wall is shown to be decisive. The precipitation of a sufficient amount of eutectic in the cast structure of a magnesium alloy ensures high soundness even in the presence of shrinkage porosity in a casting. The best tightness among the alloys is demonstrated by the EZ33A and Elektron 21 alloys, which have a sufficient amount of eutectic and a short freezing range.

关键词： Zinc-doped nanohydroxyapatite   polycaprolactone   electrospinning   membranes   physicochemical characterization   cytotoxicity assay  

摘要： Although guided tissue regeneration (GTR) is a useful tool for regenerating lost tissue as bone and periodontal tissue, a biocompatible membrane capable of regenerating large defects has yet to be discovered. This study aimed to characterize the physicochemical properties and biological compatibility of polycaprolactone (PCL) membranes associated with or without nanostructured hydroxyapatite (HA) (PCL/HA) and Zn-doped HA (PCL/ZnHA), produced by electrospinning. PCL, PCL/HA, and PCL/ZnHA were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Nanoparticles of HA or ZnHA were homogeneously distributed and dispersed inside the PCL fibers, which decreased the fiber thickness. At 1 wt% of HA or ZnHA, these nanoparticles acted as nucleating agents. Moreover, HA and ZnHA increased the onset of the degradation temperature and thermal stability of the electrospun membrane. All tested membranes showed no cytotoxicity and allowed murine pre-osteoblast adhesion and spreading;however, higher concentrations of PCL/ZnHA showed less cells and an irregular cell morphology compared to PCL and PCL/HA. This article presents a cytocompatible, electrospun, nanocomposite membrane with a novel morphology and physicochemical properties that make it eligible as a scaffold for GTR.

关键词： Deformation  

摘要： The high-strain-rate response of pure magnesium and AZ31B magnesium alloy is examined in compression and in a forced shear-loading top-hat configurations. Compression specimens loaded in the direction normal to the plane of the rolled plate (TT) display higher-strain-rate sensitivity than specimens that were loaded within the plane of the rolled plate (IP). This effect is more pronounced for pure magnesium as compared to the alloy, due to increased twinning in the IP direction as compared to the TT. Additionally, top-hat shear specimens loaded at high strain rates are observed to display stable deformation during loading, and the development of adiabatic shear bands is not observed. We hypothesize that this result is due to adiabatic heating during deformation, which enhanced the contribution of slip, lessened the role twinning, and possibly activated dynamic recrystallization processes, thus, preventing the formation of distinct shear bands.

关键词： Heat-assisted hole-clinching   Magnesium alloy   Ultra-high-strength steel   Damage·   Formability  

摘要： Due to the limited formability of magnesium alloy and ultra-high-strength steel, joining by forming of these dissimilar materials is still a big challenge, which requires suitable manufacturing technologies. To join both of the two limited formability materials, a heat-assisted hole-clinching process was investigated using numerical method and experiment test;AZ31B was chosen as the material of the upper sheet, and the numerical model was built in the DEFORM-2D software;isothermal thermo-dynamic coupling method was used to analyze the effect of upper sheet temperature on its formability during hole-clinching using the proposed numerical model and experiment tests. Meanwhile, the stress developing during hole-clinching which causes material fractures were analyzed, and damage distribution and fracture evolution were investigated. The results showed that the heat-assisted hole-clinching process can be predicted by the proposed numerical model;the formability of magnesium increased significantly as upper sheet temperature is raised;AZ31B and 22MnB5 can be joined using a hole-clinching method with the usage of heat. The results point to the applicability of the heat-assisted hole-clinching process to the joining of two limited formability materials.

关键词： magnesium alloy   electroplastic effect   stress-strain curves   tensile test   metallographic research  

摘要： In this work, a pulsed electric current is applied to a specimen simultaneously with a quasi-static uniaxial tensile load. To do so a short-time current pulse generator, inducing supercapacitors was designed and manufactured. The experiments with low operating voltage were performed at different electric current pulse period and frequency. The electroplasticity of AZ31 magnesium alloy under a pulsed electric current is investigated experimentally. Appropriate control of current parameters makes it possible to change not only the stress levels in the process, but also achieved plastic strain values. The result of the present study with low operating voltage is expected to provide a basis to develop advanced metal forming processes using electroplasticity.

关键词： structure   phase composition   parameters of high-temperature strength   deformable magnesium alloy   LPSO-phases   nanoblocks in multilayer eutectic fragments   aged condition  

摘要： Results of a study of the structure, phase composition, and main parameters of high-temperature strength of forgings from deformed magnesium alloy VMD16 of the Mg - Zn - Zr - REE system in aged condition are presented. The distinctive features of alloy VMD16 responsible for the thermal stability and high-temperature strength of the alloy are determined, which make it superior to the commercial refractory alloy MA12. It is shown that thermally stable LPSO-phases are present in alloy VMD16 in the form of nanoplates in the bulk of grains and in the form of nanoblocks in multilayer fragments of the eutectic.

关键词： Additive manufacturing   Hybrid manufacturing   Magnesium  

摘要： Additive manufad (AM) magn alloys corrode rapidly due to tensile stress and coarse microstructures. Cyclically combining (hybridizing) additive manufacturing with interlayer ultrasonic peening was proposed as a solution to improve corrosion resistance of additive manufactured magnesium WE43 alloy through strengthening mechanisms and compressive residual stress. Applying interlayer peening work hardened discrete layers and formed a glocal integrity of regional grain refinement and subsurface compressive residual stress barriers. Tensile residual stress that typically accelerates corrosion decreased 90%. Results showed time resolved control over corrosion was attainable by interlayer peening, and local corrosion within print cells decreased 57% with respect to as-printed WE43. (c) 2021 CIRP. Published by Elsevier Ltd. All rights reserved.

标准号: T/CSAE 197-2021

标准号: T/CSAE 205-2021