Papers by Keyword: Aging Process

Abstract: The effect of aging treatment on the aging hardening of 0% Yb and 0.4% Yb modified A356.2 alloy was investigated by hardness measurements and optical microscope. In this work, A356.2 was first subjected to 535°C for 5h and then subjected to 150°C, 180°C for 2h-12h hours. Results show that during aging process, there was a hardness peak along the increasing of aging temperature and time. With increasing aging progress, the morphology of Si phases became shorter and spherical. After optimum time, Si phases was coarse and the dendritic grain was broken. The peak-aged of unmodified alloys was 150°C for 10h and 180°C for 6h，and corresponding hardness values were 62.35HB and 77.10HB, respectively. With Yb addition, the hardness reached 87.58HB and 98.28HB on peak aging of 150°C/8h and 180°C/ 6h, respectively. The greatest degree of hardness was increased by 40.46% and 27.47%, combined with no Yb addition. XRD shows the interplanar crystal spacing of A356.2 with 0.4% Yb addition, which was larger than fresh A356.2 alloy. When adding 0.4%Yb under 180°C for 6h aging progress, the ultimate tensile strength was 284 MPa 12.7% increasing compared with former work.

Abstract: A356.2 aluminum alloy (Al–7Si–0.35Mg) has been widely used in automotive and aircraft industries. Previous studies found that the metamorphism effect of rare earth is better than other type of elements because of long modification time and good stability. The influence of Yb addition (0%, 0.2%, 0.4% and 0.6%) and T6 heat treatment on A356.2 alloy has been investigated in this work. The microstructures and mechanical properties of the specimen after T6 treatment were examined by optical microscope, scanning electronic microscope and tensile tests. Experimental results showed that Yb could reduce the size of α-Al and change the Si morphology from needle-like to fine spheroidal particles. With the increase of Yb content, the ultimate tensile strength increased gradually. When adding 0.4%Yb, the alloy achieved the highest ultimate tensile strength (252 MPa) and hardness (97.3HB), 10.12% and 37.66% higher than the alloy with no Yb addition. Tensile fracture analysis showed that the fracture mechanism for A356.2 aluminum alloy after T6 treatment is transgranular/intergranular mixed mode of fracture.

Abstract: Effect of Heat treatments on microstructure in a Cu-0.71Cr-0.12Zr alloy (in wt.%) have been investigated. The microstructures are analyzed by optical microscope, scanning electron microscope, transmission electron microscope and high-resolution transmission electron microscope after each step of heat treatments. The results show that the as-cast microstructure of Cu-Cr-Zr alloy is Cu matrix, Cr dendrite and eutectic structure which is composed of Cu and Cu₅Zr phase with a fine lamellar structure. By increasing the homogenization temperature or prolonging the holding time, the eutectic structure is dissolved into the matrix gradually and the volume fraction of the Cr phases is obviously reduced. The precipitation of Cr phase prevents from Zr-rich phases dissolving in the matrix. And the proper homogenizing process is 900°C×12 h. When the alloy aged at 450°C for 24 h, the crystallography of Cr precipitates and the orientation relationship between Cr precipitates and Cu matrix is bcc structure and KS-OR, respectively. The disk-shaped precipitate is identified as Cu₅Zr phase and their habit plane is parallel to {111}_Cu plane.

Abstract: In the present paper, water glass was used to synthesize silica aerogels and calcium magnesium silica aerogels. The present research was aimed to investigate the effect of gel aging time (1 and 24 hours) on the physical and surface properties of aerogels. Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, Fourier Transform Infrared spectroscopy and scanning electron microscopy techniques were used to characterize aerogels. Successful formation of nanopores (2.8-4.4 nm) was approved by N₂ adsorption/desorption isotherms. The aerogels contained porous network structure with different surface areas (388.9-729.9 m² g^-1). Aging for longer times led to an ability to decrease the density of the aerogels. The bulk density was higher in silica aerogels than in calcium magnesium silica aerogels. The well-tailored network matrix with high BET surface area (729.9 m² g^-1) and low density (0.116 g cm^-3) was achieved via 24 hours gel aging of calcium magnesium silica aerogel.

Abstract: Aging process especially in asphalt binder material can occur throughout the life cycle of asphalt pavement starting from mixing, placement and during the service life. During this process, the more stiffer and brittle of asphalt binder is produced due to age hardening and gives an indication of initial factor of deterioration in asphalt pavement. A number of noteworthy researchers have focused on oil based modification to produce modified asphalt binder by using Waste Cooking Oil (WCO), due to the presence of natural antioxidant properties possessed in WCO. Antioxidant has played the role as an oxidative inhibition and has the potential to minimize the aging rate to occur. The aging process is conducted by separating between short term and long term aging where short term oxidative aging of binders was simulated using rolling thin film oven (RTFO) while long term aging was performed using pressure aging vessel (PAV). The laboratory evaluation was carried out to investigate the relationship between the qualities of WCO that affect the availability of antioxidant amount towards the susceptibility of aging rate by conducting Dynamic Shear Rheometer (DSR). The result from rheological studies demonstrated that the lowest Aging Index (AI) is presented as 2.14, 2.18 and 1.79 for replacement by using WCO in December sample at concentration of 3%, 4% and 5% for short term aging while AI at 3% = 5.17 and 5% = 7.22 for long term aging. Therefore, the high quality of oil represented by WCO in December sample has indicated the high availability of antioxidant content that can minimize the aging susceptibility in the asphalt binder modified by WCO.

Abstract: The effect of external environment on the aging process of commercially used lime-cement plasters is studied. Three different kinds of plasters are tested at three different ages, namely in the reference state after 28 days of standard curing and after one and two years of exposure to the environmental conditions of Central Europe. The basic physical properties (bulk density, matrix density, open porosity), mechanical strengths (compressive strength, bending strength) and water vapour diffusion resistance factor belong to the studied properties. Experimental results show that not only the compressive strength but also all other studied characteristics are affected by the external environment in a significant way.

Abstract: In this study the degradation and ion/zeolite release processes of in vitro aged zeolite loaded polyurethane composites were evaluated. Two in vitro artificial aging solutions were used; artificial lysosomal fluid (ALF) and Gamble ́s solution and the total exposure time was 12 weeks. Periodically, SEM micrographs were taken of the surface of polyester type polyurethane-zeolite composites. After exposure to ALF solution the samples showed round holes and a rougher surface in general over time. Micrographs of the samples immersed in Gamble’s solution exhibited different signs of degradation with damage features on the surfaces, understood as black holes and a rougher surface pattern. In addition varying amount of salt was also observed on the surfaces that might influence the ion/zeolite release. Furthermore, the zeolite filler caused remarkable changes in mechanical properties after the aging process, which could not be discerned.

Abstract: Dynamic of phase transformation has been investigated through the measurement and analysis of relationship between electronic conductivity and the volume fraction of precipitates in the aging process of Cu-Cr-Zr alloy. According to above experiment, the Avrami empirical equation and electronic conductivity equation can be respectively confirmed at different aging temperature. S-curve of the dynamic for phase transformation at different temperature and C-curve of isothermal transformation for the Cu-Cr-Zr alloy are obtained.

Abstract: Biochar is receiving increasing attention as a promising functional material in contaminated soil remediation. However, aging processes of biochar can usually take place and affect its remediation function, because surface properties of biochar are expected to change through a variety of biotic and abiotic processes. In this review, some important influencing factors of biochar aging processes were discussed, including temperature, and soil-physical, soil-chemical and soil-biological components. It pointed out that biochar aging processes may be promoted by high temperature, protected by soil components, particularly soil organic matter (SOM), and interactions with soil microorganisms. To further prolong application of biochar in nature, biochar aging can be mitigated by its influencing factors.

Abstract: 2024 Aluminum Alloy is widely used in aeronautical applications. The Alloy's strength is increased by Precipitation Hardening which is the aging and solution of strength and is widely used in T6 state. Bearing in mind the effect of Boron in shorting the aging time, the pure material of B2O3 was used in order to add Boron to 2024 Alloy, so Alloying was done. By testing mechanical properties and microstructure observations, good results were achieved in Boron effect on this alloy's quench in comparison with those alloys lacking Boron. The outcomes depicted that this element addition increases hardness and tensile strength in aging process. In a way that the hardness of the alloy after controlled quench in one hour natural aging was reached to 93HB from 73HB and to 134HB in one hour artificial aging in 110°C. Such difference in hardness amount is due to better distribution of precipitates.