The Microstructure Evolution and Electrochemical Corrosion Behavior of 7A46 Aluminum Alloy in Different Quenching Conditions

The quenching condition of aluminum alloy can affect the mechanical property and corrosion resistance of the profile. This paper is aimed at the low quench sensitivity of aluminum alloys. Scanning electron microscopy and transmission electron microscopy were used to analyze precipitate behaviors of the 7A46 aluminum alloy under different isothermal cooling conditions and microstructure evolutions of quench-induced precipitations. The effect of the different isothermal time on the corrosion resistance of the alloy, and the relationship between microstructure and corrosion resistance after quenching were revealed through electrochemical impedance spectroscopy and potentiodynamic polarization tests. Results show that corrosion sensitivity of the quenching-aged alloy is much higher than that of the double-aged (DA) alloy, and the corrosion resistance of the quenched alloy decreases firstly and then increases. Due to the high density of the matrix precipitates, the increased content of the impurity element, the discontinuity of the grain boundary precipitates and the widening of the precipitates free zone, the most serious degree of corrosion performance among the quenched alloys is 295 °C at 800 s, and the self-corrosion potential and self-current density is −0.919 V and 2.371 μA/cm2, respectively.

KAZAKHSTAN’S NUCLEAR GOVERNANCE AS A FOREIGN POLICY ASSET

Kazakhstan’s nonproliferation initiatives are recognized worldwide. Kazakhstan is a party to almost all major nuclear treaties, a key driver in the creation of a Central Asian nuclear-weapon-free zone, initiated the Universal Declaration on Building a World Free of Nuclear Weapons, established a low-enriched uranium bank under the auspices of the IAEA in Ust-Kamenogorsk to be used for peaceful purposes in the event of a disruption in the supply of fuel for nuclear power plants.While the foreign policy acts of Kazakhstan in non-proliferation are well known and internationally appreciated, the transfer of Kazakh experience in the governance of the nuclear sector is lesser known asset. For example, the experience of the Committee for Atomic and Energy Supervision and Control and KAZATOMPROM in uranium mining and transport was shared with countries from the Southern African Development Community, under an EU project, implemented by the International Science and Technology Center. This example reveals the great potential this themes have for the further input of Kazakhstan in international development cooperation.

Modelling of liquid film migration in Al-Cu alloys

Microstructural evolution in the presence of liquid film migration (LFM) is simulated for Al-Cu alloys using a cellular automaton (CA) model. Simulations are performed for the microstructural evolution and concentration distribution in an Al-4 wt.%Cu alloy with initially equiaxed grain structures holding in a temperature gradient. A slight deviation from local equilibrium, estimated from experimental data, is considered to be the driving force for LFM. The direction of LFM is triggered by concentration fluctuations setting a concentration gradient as a further driving force. The simulation successfully reproduces the experimentally observed microstructures generated by LFM accompanied by a particle free zone behind the liquid film. The solid concentration in the particle free zone is found to be the equilibrium solid concentration. The simulated concentration profile across the migrating liquid film agrees well with experimental measurements. The simulated grain structure becomes coarser and highly elongated after holding in the temperature gradient. The results reveal that the increase in transversal grain width is mainly controlled by LFM, while the grain elongation in longitudinal direction is attributed to both LFM and temperature gradient zone melting. The solid concentration decreases from the initial (supersaturated) composition to the local equilibrium solid concentration corresponding to the local temperature. This article is part of the theme issue 'Transport phenomena in complex systems (part 2)'.

Effect of Nucleant Particle Agglomeration on Grain Size

Solute accumulation/depletion in the liquid around a growing solid particle during the solidification of metallic melts creates a constitutionally supercooled (CS) zone that has a significant effect on the final solidified grain structure. In this paper, we introduce two mechanisms related to the CS zone that affect grain size: one is the grain initiation free zone (GIFZ) that describes the inability of nucleant particles located in the CS zone for grain initiation and the other is re-melting (RM) of solid particles due to overlap of CS zones. Based on these two mechanisms, we have systematically analysed the effect of nucleant particle agglomeration on grain size. We found that nucleant particle agglomeration has a significant effect on grain size and is responsible for the discrepancy between theoretically predicted grain size and the experimental data. In addition, our numerical analysis suggests that under normal solidification conditions relevant to industrial practice solid particle re-melting has little effect on grain size and thus may be ignored during theoretical analysis. A practical implication from this work is that significant grain refinement can be achieved by dispersing the nucleant particles in the melt prior to solidification.

Obedient rebellion: conceiving the African nuclear weapon-free zone

Why do nuclear weapon-free zones (NWFZs)—areas which prohibit nuclear weapons—emerge in some contexts, and not others? Focusing on the African case, this article introduces the concept of ‘obedient rebellion’ to explain the African NWFZ's early conception. ‘Obedient rebellion’ is an attitude of ambivalence toward global nuclear order. To newly-decolonizing African states, the African NWFZ symbolized both postcolonial anti-nuclear solidarity and nuclear responsibility; it represented both ‘obedience’ to—and ‘rebellion’ against—global nuclear order. This ambivalence, between ‘obedience’ and ‘rebellion’, paradoxically accommodated multiple conflicting audiences simultaneously, thereby stabilising the zone. The African NWFZ's ambiguous meanings made it viable, even though those meanings conflicted. The zone's early conception offers insight into the complex, contending forces that continue to bind the world's NWFZs—and indeed nuclear order itself—to the present. NWFZs epitomize the tensions which stabilize nuclear order: between sovereign equality and nuclear inequality; between local solidarities and global loyalties; and between contestation and compromise. At first, these tensions seem to imperil NWFZs; in fact, these tensions stabilize NWFZs. The African zone also poses challenges to the African blind spot that continues to exist in International Relations theory.

Car Free Zone as Planning Vision to Enhancements Transportation in City Centers (Holy Najaf City Center-Iraq)

The idea of a car-free city represents a solution to the problem of fuel consumption and air pollution caused by the use of cars and replaces the idea of owning and using private cars with an efficient transportation system, and it doesn’t mean living without cars, because cars have become an integral part of a modern city. On the contrary, people can still drive in city but will not park their cars at home. Instead, they park elsewhere on their way home. Research problem: Weak regulation of the movement of vehicles in the center of the holy city of Najaf, which leads to the danger of pedestrian movement in the city center. The aim of the research: to provide a safe and effective movement for pedestrians in the center of the holy city of Najaf. Research hypothesis: The use of the car-free zone strategy in the city center transportation system achieves security for the population in the old city. The research examines reasons behind suggesting free-of-vehicle areas It gives a number of policies to achieve the strategy in the center of the holy city of Najaf, including the provision of public transportation, furniture and comfort for pedestrians in the streets, as well as easy access for the residents of the area. Thus, it is possible to draw the conclusion that there is a possibility to achieve this strategy in religious centers according to a number of policies that suit the specificity of the area.

Effect of grewia hirsuta vahl ethanolic root extract on cognition in scopolamine induced amnesia

Objective Alzheimer's illnesses are becoming medical nightmares because there is no exact solution and existing nootropic medicines (Piracetam, tacrine, and metrifonate) have significant drawbacks. The goal of this study was to see if the ethanolic root extract of Grewia hirsuta (ERGH) could improve memory in rats who had been given scopolamine. Materials and procedures At rats, ERGH was given orally in dosages of 200 and 400 mg/kg for 28 days, followed by Scopolamine (18 mg/kg i.p.) from the 25th to the 27th day. The usual nootropic drug was piracetam (200 mg/kg). The elevated plus maze (EPM), Morris water maze (MWM), and passive avoidance (PA) paradigms are used to assess cognitive functioning. Invivo anti-oxidant activity and brain acetylcholine esterase (AchE) activity were assessed. Results: At the indicated doses, ERGH extract showed a substantial memory-enhancing activity by decreasing the transfer latency in EPM, increasing the escape latency in MWM, and increasing the shock-free zone in PA. In scopolamine-induced amnesia rats, pretreatment with ERGH resulted in a significant drop in AchE enzyme, an increase in enzymatic antioxidant, and a decrease in MDA levels. Conclusion Because of its several favorable benefits, such as memory-improving properties, anticholinesterase activity, and antioxidant activity, ERGH may prove to be a useful drug in the current study, and it would be important to investigate its potential in the care of Alzheimer's patients.

Microstructure and Hot Workability of Twin-roll Cast Dispersoid-strengthened Al- Mg-Si-Mn alloys

Dispersoid-strengthened Al-Mg-Si-Mn aluminum alloys were produced by twin-roll casting (TRC) and conventional mold casting (MC). An extra-low temperature homogenization was performed at temperature of 430 °C for 6 h, which was followed by uniaxial hot compression tests. The results showed that the as-cast TRC samples had a lower eutectic fraction with a smaller size and a higher solid solution concentration compared to the as-cast MC samples. During the extra-low temperature homogenization, a large number of α-Al(Fe, Mn)Si dispersoids precipitated, and the dispersoids in the TRC sample had a greater number density than those in the MC sample. Precipitation-free zone (PFZ) formed near the eutectic regions, TRC sample had a lower PFZ fraction than that of MC sample. The TRC samples yielded higher flow stresses of hot deformation than MC sample owing to the stronger dispersoid strengthening effect. Severe edge cracking occurred in the deformed MC samples due to the high fraction of coarse AlFeMnSi intermetallic particles, no edge crack formed in the TRC samples owing to its lower fraction and fine intermetallics which improved the hot workability of TRC sample.