Papers by Keyword: Aging Behavior

Abstract: The marine atmospheric environment exposure test of BL-60 basalt composites was carried out in Hainan test station. The effects of marine atmospheric environment on the aging behavior of composites were studied by macro and micro morphology, moisture absorption rate, bending strength, linear expansion coefficient, glass transition temperature and infrared spectrum. The results show that the moisture absorption of the composite matrix plays a dominant role in the initial stage of exposure to the marine atmospheric environment ( 0.25 years ). With the extension of the test time ( ≥0.5 years ), the surface epoxy resin is aged and the basalt fiber is exposed. The intensity of the resin characteristic peak is obviously weakened, and the resin pulverization and shedding are greater than the moisture absorption effect. After one year of exposure to the marine atmospheric environment, the basalt fiber is almost completely exposed to the surface and exhibits a uniform cross-woven structure, and the resin characteristic peaks all disappear. After exposure to marine atmospheric environment for 1.5 years, the glass transition temperature of the composites decreased from 116.9 °C to 82.79 °C, the linear expansion coefficient decreased from 49.65 μm/(m·°C) to 31.43 μm/(m·°C), and the bending strength decreased from 570 MPa to 513 MPa. The experimental results show that the marine atmospheric environment causes aging damage to the hygroscopicity, macro and micro morphology and chemical structure of BL-60 basalt composites, which leads to the decrease of thermal and bending properties.

Abstract: The aging behavior of a cast Al-2 wt.% Fe alloy processed by High-Pressure Torsion (HPT) at room temperature was studied by subsequent aging treatments at 200 °C. Observations by Transmission Electron Microscopy (TEM) revealed that the microstructure after HPT processing reached an ultrafine-grained level with an average grain size in the Al matrix of ~120 nm. The initial eutectic structures were fragmented into particles with sizes of less than 400 nm and partially dissolved in the matrix up to a supersaturated Fe content of ~1% as confirmed by X-Ray Diffraction (XRD) analysis. The peak-age condition was achieved within 0.25 h of aging, which provides the maximum hardness of ~200 HV. Analyses by high-resolution S/TEM show that round particles of Al₆Fe with sizes of ~5-10 nm and semi-coherent with the matrix are the dominant precipitates in the peak-aged condition. The hardness increases by aging for 12 h above the as-HPT-processed level of 185 HV. The dominant precipitate phase transforms to Al₃Fe in the over-aged condition with a loss of coherency during growth. Enhanced precipitation kinetics was observed because of high density of lattice defects induced by the HPT processing, which were also confirmed by significant recovery in the electrical conductivity of the samples after aging.

Abstract: In present study, the aging behavior of the hot extruded semi-solid Mg-10Al-0.3Mn alloy was investigated. In order to obtain the extruded bar, we carried out the hot extrusion at 380°C with an extrusion ratio of 25 and ram speed of 2.4mms-1. Vickers hardness test, electrical conductivity measurements, scanning and transmission electron microscopy and tensile testing were performed to identify the aging behaviors and mechanical properties during the aging treatment. Observations of the aging behavior and results of the tensile tests after the T6 heat treatment at each aging temperature show that the optimum aging conditions was indicated by a hardness increment of 72% and a tensile strength of 340MPa in the extruded bar.

Abstract: Our recent studies showed that continuous and cellular precipitates are covered with the whole of crystal grain in age hardable AM60 magnesium alloy cast into permanent molds, which have the average grain size of 75-85μm. Also, continuous precipitation is generated nearby grain boundary in the same alloys cast into sand molds, which have the average grain size of 138-147μm. It’s thought that permanent mold castings have the age hardening behavior of intragranular precipitation participation type that is influenced by continuous precipitates. It’s also thought that sand mold castings have the age hardening behavior of grain boundary participation type that is influenced by cellular precipitates. In this study, AM60 magnesium alloy with larger grain size was used to detect the grain size dependence of microstructure and aging behavior. In the microstructure of as-cast condition, the larger the grain size, it was shown that the none-equilibrium crystallized β phase with eutectic reaction during the solidification between liquidus and solidus temperatures becomes large-size. In the age hardening curves, the peak hardness values become higher with decreasing of grain size.