Introduction and Objectives: Due to the negative impact of increasing Mg content on the ductility and toughness of Zn-Mg alloys, the use of dilute forms of these alloys has recently become more widespread. In this study, the effect of chill modification and friction stir processing (FSP) on the microstructure and corrosion behavior of dilute Zn-0.3Mg alloy were studied. Materials and Methods: The FSP was performed using a simple cylindrical tool under rotation speed of 1600 rpm and travel speed of 12 mm/min on solidified alloy at a cooling rate of 4.1 °C/s. To investigate the effect of chill modification, the solidification rate was increased from 4.1 to 14.7 °C/s. Tafel polarization and electrochemical impedance spectroscopy (EIS) experiments were performed in simulated body fluid (SBF). Results: The Tafel polarization test results indicated that the corrosion current densities of the chill-modified alloy (20.9 µA/cm2) and friction stir processed alloy (19.6 µA/cm2) are lower than that of the as-cast alloy (38.8 µA/cm2) by about 46 and 49%, respectively. The EIS also implied increasing corrosion resistance of the as-cast alloy from about 50 Ω to 85 Ω and 1.5 kΩ in the chill modified and friction stir processed samples, respectively. Conclusion: Due to the ultrafine and homogenous distribution of Mg2Zn11 particles and development of ultrafine grains (increasing the grain boundary density), the surface of the processed samples (especially the friction stir processed ones) are covered by a continuous and compacted layer composed of corrosion products causing improved corrosion resistance of Zn-0.3Mg alloy.
In this manuscript, we prove the existence of strictly positive solutions for a class of p&q systems whose nonlinearities involved may exhibit semipositone behavior, which arise naturally in several applications that includes models of competing species and the dynamics of particle movement. Our approach combines variational methods, comparison principles and a novel regularity result for systems. This estimate, which may be of independent interest, is new even in the classical Laplacian case.
The petroleum and petrochemical industries operate in highly aggressive environments where corrosion can severely compromise the integrity of critical equipment. This work investigates how key high-velocity oxygen fuel (HVOF) spraying factors influence the coating integrity and corrosion performance of tungsten carbide layers deposited on AISI 4130 steel. The powder feed rate (ranging from 60 to 80 g/min) and spray pressure (ranging from 6.5 to 7.4 bar) were systematically varied for samples C1-C5, while an uncoated specimen served as the control. Microstructural characterization using scanning electron microscopy confirmed variations in coating density and thickness across the samples. Mechanical performance was evaluated through Vickers hardness measurements, indicating a significant increase (from 225 HV for the uncoated steel to 2060 HV and 2020 HV for samples C3 and C5, respectively). Corrosion performance was examined using Tafel polarization testing and EIS (electrochemical impedance spectroscopy). The HVOF-processed coatings significantly enhanced corrosion resistance compared with the bare substrate, with sample C3 demonstrating the lowest corrosion current density and a more noble corrosion potential. Nyquist analysis further indicated that C3 possessed the highest charge-transfer resistance due to its uniform WC distribution and reduced porosity. Overall, the optimal performance was achieved using a spray pressure of 7.2 bar and a powder feed rate of 72 g/min, identifying sample C3 as the most effective configuration for corrosion protection.
This study investigates the combined effects of silica fume addition and variable steam-curing durations on concrete mechanical properties. Unlike most prior research, which typically used fixed steam durations and focused mainly on compressive strength, this work directly compares multiple steam-curing intervals (4–48 h at 66 ± 2 °C) with conventional water curing (3–28 days), enabling clear one-to-one comparisons of compressive, splitting tensile, and flexural strength development. Four mixtures were tested: control mixes at w/c 0.6 and 0.35 (no silica fume), plus mixes with silica fume added at 10
Accurate flood and damage forecasting is essential for mitigating the severe impacts of floods, which affect millions of people worldwide and cause substantial economic losses each year. This study evaluates the efficacy of the Weather Research and Forecasting (WRF) model in simulating precipitation for flood forecasting and direct damage estimation in the Poldokhtar basin, Iran. By testing 87 WRF configurations, optimal schemes (e.g., WSM3, Kessler, Grell 3D, and YSU) were identified for accurate precipitation and flood simulation. The WRF outputs were coupled with the HEC-HMS and HEC-RAS models to simulate flood hydrographs and hydraulic characteristics. The integrated modeling framework achieved Nash-Sutcliffe efficiency values above 0.85 and peak discharge errors below 15
