Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy

Local corrosion mechanism of an Al-Zn-Mg-Cu alloy in oxygenated chloride solution: Cathode activity of quenching-induced η precipitates

It is known that parameters such as deformation together with the temperature and time of aging heat treatment, play critical roles in changing the mechanical properties and the microstructure of AA2024 aluminum alloy. It is shown that a superior level of strength is achievable by applying cold deformation at an appropriate combination of temperature and time. In the present study, the effect of cold deformation on the various properties of artificially aged AA2024 aluminum alloy was assessed. Two cold rolling amounts of 25% and 50% were exerted after solution treatment at 500 °C for 1 h, followed by quenching. The samples were then aged at 180 °C for 2 h, 200 °C for 4 h and 220 °C for 6 h. The microstructure of the samples was examined by Optical microscope, Field Emission Scanning Electron Microscope (FESEM), and High Resolution Transmission Electron Microscope (HRTEM). The Mechanical properties were assessed by tensile and hardness tests. As well, electrical conductivity measurement was used to evaluate the state of precipitation. Results showed that if cold deformation is properly applied, the mechanical properties of the aged samples increase substantially at 180 °C for 2 h. This condition was recognized as the peak aging condition. In a sense, results showed that applying cold deformation would significantly influence on the aging treatment parameters. The cold rolled samples aged at 180 °C for 2 h showed the highest flow stress, but with slightly reduced elongation. Results also showed that aging at 200 °C and 220 °C reduced the strength to the level below the as cold rolled conditions due to the over aging process. High resolution TEM studies confirmed the aged hardening precipitates of the S′ type. Using HRTEM the early stages of these precipitates (i.e. Guinier–Preston–Bagaryatsky (GPB) zone) were explored. The grown state of the S′ precipitates in the form of S (Al2CuMg) type precipitates was also determined in the overaging conditions using the TEM approach. Finally, as an assessment of mechanical properties was performed, taking into account the three parameters of precipitation hardening, recovery and grain growth.

TEM study of S' hardening precipitates in the cold rolled and aged AA2024 aluminum alloy: influence on the microstructural evolution, tensile properties & electrical conductivity

The softening phenomenon of age-hardening aluminum alloy-welded joints is severe during conventional fusion welding, which increases the likelihood of stress and strain concentration in the joint during the period of service, significantly reduces the mechanical properties compared to the base metal, and represents an obstacle to the exploration of the potential structural performance. This review paper focuses on an overview of the softening phenomenon. Firstly, the welding softening mechanism and the characteristics of age-hardening aluminum alloys are clarified. Secondly, the current main research methods that can effectively improve joint softening are summarized into three categories: low-heat-input welding, externally assisted cooling during welding, and post-weld treatment. The strengthening mechanism and performance change rule of age-hardening aluminum alloy joints are systematically analyzed. Finally, this paper considers the future development trends of further research on joint softening, and it is expected that interest in this topic will increase.

Review of Techniques for Improvement of Softening Behavior of Age-Hardening Aluminum Alloy Welded Joints.

Comprehensive review of nickel-based catalysts advancements for CO2 methanation

The effect of solution-treating temperature of 465–495 °C on the intergranular corrosion (IGC) susceptibility of the peak-aged Al-Zn-Mg-Cu alloy (7050) is investigated. The accelerated corrosion test results show that the IGC susceptibility first decreases and then increases with increasing the solution-treating temperature. Whereas, an opposite change is observed for the Cu content in grain boundary η-Mg(Zn,Cu)2 precipitates based on the quantitative measurement and modeling of grain boundary segregation and precipitation. Furthermore, the change in IGC susceptibility is explained by the electrochemical microcouples between grain boundary η-Mg(Zn,Cu)2 precipitates and precipitation-free zones (PFZs), of which the driving force varies with the Cu content in the η-Mg(Zn,Cu)2 precipitates due to different solution-treating temperatures.

Effect of solution-treating temperature on the intergranular corrosion of a peak-aged Al-Zn-Mg-Cu alloy

Storing and in-situ hydrogenating CO2 to CH4 by dual functional materials (DFMs) is an efficient solution to alleviate the greenhouse effect and energy shortage. However, in the multi-step preparation process of DFMs, high-temperature calcination is usually required, solvent is used, and NO2/CO2 is inevitably emitted. In this work, we first reported that the Ni/MgO DFMs could be mechanochemically synthesized in one step at room temperature by magnesium-induced hydrogenation of Ni-mixed magnesium carbonate without using any solvent and NO2/CO2 emission. Integrated CO2 capture and methanation performance of the Ni/MgO DFMs are investigated isothermally in a TG-MS apparatus and a fixed bed reactor. The CO2 uptake and CH4 yield over the 80Ni/MgO DFM at 300 ℃ are 0.37 mmol/g and 0.27 mmol/g, respectively, with a CO2 conversion of 73.0 % and CH4 selectivity of 100 %. After 5 consecutive CO2 capture and methanation cycles at 300 ℃, the CO2 uptake and CH4 yield over the 50Ni/MgO DFM still are 0.26 mmol/g and 0.18 mmol/g, respectively, with a CO2 conversion of 69.2 % and CH4 selectivity of 100 %. Furthermore, the mechanism of CO2 adsorption, activation, and hydrogenation to methane over the Ni/MgO DFM is systematically investigated by using density functional theory (DFT) calculations. This study offers an alternative, green, and sustainable strategy to acquire DFMs for CO2 capture and methanation. 

Mechanochemical synthesis of Ni/MgO dual functional materials at room temperature for CO2 capture and methanation

Storing and hydrogenating CO2 to CH4 is an efficient solution to alleviate the greenhouse effect and energy shortage. This work demonstrated that the CaO-captured CO2 could be selectively converted to CH4 by Ni- and hydrogen-assisted calcium looping (CaL) processes in a batch reactor. The Ni/CaO composite was first synthesized in one step at room temperature by calcium-induced hydrogenation of Ni-mixed calcium carbonate without the use of any solvent and CO2 emission. The CO2 capture properties over the Ni/CaO composite and the methanation properties of the Ni/CaCO3 composite produced after CO2 capture were then studied in a batch reactor. It was proved that the CO2 capture properties of CaO can be improved, the CaO recovering temperature can be significantly lowered, and valuable CH4 can be selectively produced by Ni- and hydrogen-assisted calcium looping processes at moderate/high temperature. The 68.58% methane yield and 100% methane selectivity were achieved under relatively mild conditions. After five Ni- and hydrogen-assisted CaL processes, the methane yield still reaches 45%. This study offers a novel energy-saving CaL process, which can be utilized for facile and selective conversion of the CaO-captured CO2 to CH4. 

Selective Conversion of the CaO-Captured CO2 to CH4 by Ni- and Hydrogen-Assisted Calcium Looping Processes in a Batch Reactor

CO2 capture and selective methanation were realized over a greenly prepared Ni/CaO/Al2O3 composite at as low as 200 °C under static pressure conditions.

Low-temperature conversion of CaO-captured CO2 to CH4 over a greenly prepared Ni/CaO/Al2O3 composite under static pressure conditions

MgH2-modified Ni catalysts with electron transfer behavior for improving CO2 methanation.

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