Effect of Dissolution of η′ Precipitates on Mechanical Properties of A7075-T6 Alloy

The effects of dissolution of the η′ phase by solution treatment on the mechanical properties of A7075-T6 alloy were investigated. Immediately after solution treatment of the T6 sheet at 450 oC or higher, elongation significantly increased and dissolution of the η′ phase occurred. η′ is the main hardening phase. After natural-aging, GPI, which is coherent with the aluminum matrix, was formed and strength increased. When bake hardening after natural-aging was performed, the yield strength slightly increased due to partial dissolution of the GPI and re-precipitation of the η′ phase. In contrast, after solution treatment at 400 oC, there was less elongation increase due to the precipitation of the coarse η phase at grain boundaries and low dissolution of the η′ phase. In addition, when bake hardening after natural-aging was performed, the yield strength decreased due to insufficient GPI, which is the nucleation site of the η′ phase. To promote reprecipitation of the η′ phase, the solution treatment temperature was set to a level that would increase solubility. As a result, the yield strength was significantly increased through re-precipitation of a large number of fine and uniform η′ phase. In addition, to increase the effect of dissolution, a pre-aging treatment was introduced and the bake hardenability can be improved after dissolution.

Effects of Si and Sn Contents and Heat-Treatment Temperature on the Corrosion Behavior of AISI 439 Ferrite Stainless Steel

This study was conducted to evaluate the corrosion resistance and optimize the heat-treatment process of AISI 439 ferrite stainless steel silicon and tin alloys with reduced chromium. The microstructure of the specimens and deposition under each condition were analyzed. The production of oxide films was compared based on the thickness of the film and the change in the contents of each element. In addition, electrochemical analyses of each heat-treatment condition was used to quantitatively compare corrosion resistance and passive film stability based on the relative chromium, silicon, and tin contents. It was found that the addition of silicon and tin compensated for the decrease in corrosion resistance induced by the chromium reduction. The addition of the two elements inhibited iron (Fe) oxide production in the surface oxide film, thereby improving the corrosion resistance of the material and improving the stability of the passive film. Moreover, the SiO2 and SnO2 layers inhibited the production of Fe oxide and contributed to the stability of the film along with Cr2O3, the main component of the passive film. However, when the heat treatment temperature increased above a specific temperature, the oxide inhibitory effect of the two elements was relatively offset. Nevertheless, further research to optimize the content of the three elements will help develop materials with superior mechanical properties and corrosion resistance.

High-loading Ga-exchanged MFI zeolites as selective and coke-resistant catalysts for nonoxidative ethane dehydrogenation

In this paper, we investigated the effects of Ga loading amount and H2 treatment temperature for reductive solid-state ion-exchange reaction on the generated Ga species in Ga-exchanged MFI zeolites (Ga-MFIs)...

Erianthus Plant: A Rich Silica Source for Extraction of Amorphous Silica

In this paper, Erianthus plant, a grass type of lignocellulosic biomass, is presented as an alternative source for the production of amorphous silica. Thermal treatment (combustion) of Erianthus plant under a controlled temperature of 600–900°C produces Erianthus Ash (EA). Then, silica powder was extracted from EA by the chemical extraction method. In this work, the effect of treatment temperature on the preparation of EA and extracted silica is studied. The EA samples and extracted silica are noted as EA600 – EA900 and Si600 – Si900 respectively with respect to the treatment temperature. To evaluate the effect of the concentration of NaOH solution on the purity of silica, NaOH solution (2–3 N) is verified in this work. The results revealed that the pure amorphous silica can be extracted using a 2.5 N NaOH solution from EA800. The percentage of amorphous silica with a purity of about 99% was confirmed by X-Ray Fluorescence (XRF).

Microstructure and Mechanical Property of Al6Si2Cu Alloy Subjected to Double-Solution Heat Treatment

This study aims to develop the mechanical properties of the Al6Si2Cu aluminum alloy through the double-solution treatment. In addition to the Al matrix, large amounts of coarse eutectic Si, Al2Cu intermetallic, and Fe-rich phases were generated through thermo-calc simulation in agreement with the equilibrium phases. The eutectic Si phase is fragmented and spheroidized by the solution treatment as the heat treatment temperature and time increase. The Al2Cu intermetallic phase is dissolved into the Al matrix, resulting in an increase in both strength and elongation. The second-step solution temperature at 525 °C should be an optimum condition for enhancing the mechanical properties of the Al6Si2Cu aluminum alloy.

Thermosetting Binder for Fibrous Insulating Materials

Постановка задачи. Модернизация систем изоляции инженерных сооружений, в том числе и трубопроводов и промышленных объектов, направлена как на решение общих задач энергоэффективности, так и частных задач теплосбережения и экологической безопасности. В связи с этим разработка и применение связующего, отверждаемого при значительно меньших температурах и не содержащего фенолы, является актуальной задачей. Результаты. Эксперимент, проведенный для оценки влияния на адгезию к различным поверхностям комплексного связующего, отверждаемого в температурном интервале от 80 до 140 С, позволил определить оптимальные расходы латентного компонента и модификатора, которые составили соответственно 3,6-4,0 % и (2,6 ± 0,1) % по массе связующего при оптимальной температуре тепловой обработки 100 С. Расчетом установлено, что при переходе от тепловой обработки при 250 С к тепловой обработке при 100 С прямые затраты тепла снижаются на 60 %, а энергетические затраты на изготовление минераловатных цилиндров на 20-30 %. Выводы. Теоретически обоснована и экспериментально подтверждена возможность применения эпоксидного клея на латентных отвердителях в качестве связующего для высокопористых систем с распределением и отверждением этого связующего на тонких минеральных волокнах. Определены характеристические параметры процесса отверждения, длительность которого уменьшается с повышением температуры и содержания латентного отвердителя. Statement of the problem. The modernization of insulation systems of engineering structures, including pipelines and industrial facilities, is aimed both at solving general problems of energy efficiency, as well as the particular tasks of heat saving and environmental safety. Therefore the development and use of a binder that cures at much lower temperatures and does not contain phenols is an urgent task. Results. An experiment conducted to assess the effect on adhesion to various surfaces of a complex binder cured in the temperature range from 80 to 140 °C allowed us to determine the optimal flow rate of the latent component and modifier, which were 3.6-4.0 % and (2.6 ± 0.1) % respectively by the weight of a binder at an optimal heat treatment temperature of 100 °C. The calculation suggests that when switching from heat treatment at 250 °C to heat treatment at 100 °C, direct heat costs are reduced by 60 %, and energy costs for the manufacture of mineral wool cylinders by 20-30 %. Conclusion. The possibility of using epoxy glue on latent hardeners as a binder for highly porous systems with the distribution and curing of this binder on thin mineral fibers has been justified theoretically and confirmed experimentally. The characteristic parameters of the curing process have been identified whose duration decreases as temperature and the content of latent hardener increase.

Research of the Structure and Physical-Mechanical Properties of Modified Clay

The article presents the properties of natural clay in Uzbekistan. The historical analysis of the use of this natural raw material is presented. Possibilities of changing the properties of clay by introducing synthetic fibers of light industry waste into it are considered. Calculations of the properties of clay with the introduction of various additives and the technology of its processing are given. It has been established that modification of clay with fibrous waste and subsequent heat treatment improves frost resistance, and water resistance of the material, these properties depend on the percentage of fiber content, heat treatment temperature and time of holding the material in the furnace.