Investigating the Influence of Mg Content Variations on Microstructures, Heat-Treatment, and Mechanical Properties of Al-Cu-Mg Alloys.

The objective of this study was to examine the impact of varying magnesium levels in the α-Al + S + T region of the Al-Cu-Mg ternary phase diagram on the solidification process, microstructure development, tensile properties, and precipitation hardening of Al-Cu-Mg-Ti alloys. The outcomes indicate that alloys with 3% and 5% Mg solidified with the formation of binary eutectic α-Al-Al2CuMg (S) phases, whereas in the alloy with 7% Mg, the solidification process ended with the formation of eutectic α-Al-Mg32(Al, Cu)49 (T) phases. Additionally, a significant number of T precipitates were noticed inside the granular α-Al grains in all alloys. In the as-cast condition, the 5% Mg-added alloy showed the best combination of yield strength (153 MPa) and elongation (2.5%). Upon T6 heat treatment, both tensile strength and elongation increased. The 7% Mg-added alloy had the best results, with a yield strength of 193 MPa and an elongation of 3.4%. DSC analysis revealed that the increased tensile strength observed after the aging treatment was associated with the formation of solute clusters and S″/S' phases.

Microstructure Evolution and Mechanical Properties of Al-Cu-Mg Alloys with Si Addition.

The aim of this study was to investigate the impact of the addition of a minor quantity of Si on the microstructure evolution, heat treatment response, and mechanical properties of the Al-4.5Cu-0.15Ti-3.0Mg alloy. The microstructure analysis of the base alloy revealed the presence of α-Al grains, eutectic α-Al-Al2CuMg (S) phases, and Mg32(Al, Cu)49 (T) phases within the Al grains. In contrast, the Si-added alloy featured the eutectic α-Al-Mg2Si phases, eutectic α-Al-S-Mg2Si, and Ti-Si-based intermetallic compounds in addition to the aforementioned phases. The study found that the Si-added alloy had a greater quantity of T phase in comparison to the base alloy, which was attributed to the promotion of T phase precipitation facilitated by the inclusion of Si. Additionally, Si facilitated the formation of S phase during aging treatment, thereby accelerating the precipitation-hardening response of the Si-added alloy. The as-cast temper of the base alloy displayed a yield strength of roughly 153 MPa, which increased to 170 MPa in the Si-added alloy. As a result of the aging treatment, both alloys exhibited a notable increase in tensile strength, which was ascribed to the precipitation of S phases. In the T6 temper, the base alloy exhibited a yield strength of 270 MPa, while the Si-added alloy exhibited a significantly higher yield strength of 324 MPa. This novel Si-added alloy demonstrated superior tensile properties compared to many commercially available high-Mg-added Al-Cu-Mg alloys, making it a potential replacement for such alloys in various applications within the aerospace and automotive industries.

Image quality enhancement in variable-refresh-rate AMOLED displays using a variable initial voltage compensation scheme.

In active matrix organic light emitting diode (AMOLED) displays, when a variable refresh rate is applied and the frame rate changes, the image's color and luminance quality in AMOLED displays deteriorates. The frequency-dependent cognitive differences were experimentally demonstrated by using 6.76″ AMOLED displays. This phenomenon is dependent on the emission time and the data programming time on the frame rate. This degradation of the image quality during the frequency switch could be prevented by applying a variable initial voltage (VINI) to the OLED anode. For a frequency change between 60 and 120 Hz, the measured just noticeable color difference (JNCD) decreased from 7.50 to less than 1.00 in luminance, and from 2.34 to 0.02 in color. As our approach can prevent image quality distortion by utilizing an existing compensation pixel structure without additional compensation steps, it will be a promising technique for improving the picture quality in AMOLED displays.

Effect of Al2Ca Addition and Heat Treatment on the Microstructure Modification and Tensile Properties of Hypo-Eutectic Al-Mg-Si Alloys.

The current study investigated the microstructure modification in Al-6Mg-5Si-0.15Ti alloy (in mass %) through the minor addition of Ca using Mg + Al2Ca master alloy and heat treatment to see their impact on mechanical properties. The microstructure of unmodified alloy (without Ca) consisted of primary Al, primary Mg2Si, binary eutectic Al-Mg2Si, ternary eutectic Al-Mg2Si-Si, and iron-bearing phases. The addition of 0.05 wt% Ca resulted in significant microstructure refinement. In addition to refinement, lamellar to fibrous-type modification of binary eutectic Al-Mg2Si phases was also achieved in Ca-added (modified) alloy. This modification was related to increasing Ca-based intermetallics/compounds in the modified alloy that acted as nucleation sites for binary eutectic Al-Mg2Si phases. The dendritic refinement with Ca addition was related to the fact that it improves the efficacy of Ti-based particles (TiAl3 and TiB2) in the melt to act as nucleation sites. In contrast, the occupation of oxide bifilms by Ca-based phases is expected to force the iron-bearing phases (as iron-bearing phases nucleate at oxide films) to solidify at lower temperatures, thus reducing their size. The as-cast microstructure of these alloys was further modified by subjecting them to solution treatment at 540 °C for 6 h, which broke the eutectic structure and redistributed Mg2Si and Si phases in Al-matrix. Subsequent aging treatment caused a dramatic increase in the tensile strength of these alloys, and tensile strength of 291 MPa (with El% of 0.45%) and 327 MPa (with El% of 0.76%) was achieved for the unmodified alloy and modified alloy, respectively. Higher tensile strength and elongation of the modified alloy than unmodified alloy was attributed to refined dendritic structure and modified second phases.

Intergranular Corrosion and Microstructural Evolution in a Newly Designed Al-6Mg Alloy.

In this work, the microstructure and corrosion behavior of a novel Al-6Mg alloy were investigated. The alloy was prepared by casting from pure Al and Mg+Al2Ca master alloy. The ingots were homogenized at 420 °C for 8 h, hot-extruded and cold-rolled with 20% reduction (CR20 alloy) and 50% reduction (CR50 alloy). The CR50 alloy exhibited a higher value of intergranular misorientation due to a higher cold rolling reduction ratio. The average grain sizes were 19 ± 7 µm and 17 ± 9 µm for the CR20 and CR50 alloys, respectively. An intergranular corrosion (IGC) behavior was investigated after sensitization by a nitric acid mass-loss test (ASTM G67). The mass losses of both the CR20 and CR50 alloys were similar at early periods of sensitization, however, the CR20 alloy became more susceptible to IGC as the sensitization time increased. Grain size and ß phase precipitation were two critical factors influencing the IGC behavior of this alloy system.

Effect of Cu Addition on the Precipitation Hardening and Mechanical Properties of Al-Mg Based Cast Alloys.

This study examines the formation of different phases of Al-6 mass% Mg-xCu (x = 1 and 3 mass%) alloys in as-cast condition. Further, it investigates the dissolution of these phases upon solution heat treatment (SHT) and studies the precipitation behavior of these ternary alloys. Scanning electron microscopy with energy-dispersive spectrometry and high resolution X-ray diffraction analyses show the presence of the second phases of Al3Mg2 (ß), Al6CuMg4 (T), and Al2CuMg (S) in Alloy I (Al-6Mg-1Cu), whereas Alloy II (Al-6Mg-3Cu) had only T and S second phases (with a much higher number of S phases). Upon SHT, a significant number of eutectic phases were dissolved in Alloy I, whereas in Alloy II, the number of undissolved S phases was relatively high. A differential scanning calorimetry (DSC) analysis of experimental alloys in as-quenched states reveals two exothermic peaks related to the formation of nanoclusters and S″ or S' metastable phases. Both alloys undergo a rapid hardening stage during the aging process, in which approximately 50%-60% of total hardness was achieved. This is attributed to the formation of nanoclusters. The maximum yield strength achieved at the peak hardness condition was approximately 200 MPa for Alloy I, whereas it was approximately 160 MPa for alloy II. Alloy I took a long time to reach peak hardness, which is correlated with the stability of nanoclusters for a longer time. Earlier peak hardness in Alloy II, despite having nanoclusters, is correlated with undissolved eutectic phases acting as heterogeneous nucleation sites for the formation of S″ or S' metastable phases.

Influence of Si Content on Tensile Properties and Fractography of Al-Mg-Si Ternary Alloys.

This study investigated the heat treatment response and tensile properties of Al-6 mass%Mg-xSi (x = 1, 3, 5, and 7 mass%) ternary alloys. Further, the fracture behavior of these alloys in response to heat treatment for different temper conditions was also examined. Scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS) analysis of the as-cast alloys revealed, in all of them, the presence of iron-bearing phases (in a size range of 10˜60 µm) that did not dissolve or become refined upon heat treatment. Additionally, eutectic Mg2Si and Al3Mg2 phases were found in Alloy I (Al-6Mg-1Si), while eutectic Mg2Si and Si phases were found in the rest of the alloys. In the as-cast condition, the tensile properties of the examined alloys decreased in relation to increasing Si content. Nonetheless, after heat treatment, the yield strength of the alloys with high Si content (>3 mass%) increased significantly compared with that in the as-cast condition. A yield strength greater than 300 MPa was achieved in both Alloy III (Al-6Mg-5Si) and Alloy IV (Al-6Mg-7Si), although this was achieved at the expense of ductility. According to the fractography of the tensile-fractured surfaces undertaken using optical and scanning electron microscopy, fractures of the iron-bearing phases were found to be the source of cracking in alloys with high Si content. In the case of those with low Si content (≤3 mass%), cracks were believed to have been caused by the debonding of iron-bearing phases from the aluminum matrix.

Correlation of Surface Oxidation and Mg-Based Intermetallic Phases in Grain Boundaries of Al-Mg Alloys Containing Third Elements.

In this study, the correlation of surface oxidation and Mg-based intermetallic phases in the grain boundary in Al-Mg alloys containing third elements was investigated. The experimental results were examined by phase diagrams plotted as a function of oxygen partial pressure determined by thermodynamic calculation. The addition of Si and Cu as third elements into the Al-7 mass%Mg alloy formed Mg-based secondary phases during solidification. The 1 mass% Cu addition formed three different types of Mg-based intermetallic compounds. From weight gains by oxidation, all samples exhibited their weight gains depending on time. The Si-added alloy showed a considerably lower weight gain and maintained a nearly constant weight, while the weight gain of the Al-7 mass%Mg-1 mass%Cu alloy was significantly greater than those of other alloys. MgO and MgAl2O4- spinel were the main oxides that formed the oxide scale in all examined alloys. Si addition formed the multi-element oxide including Mg and Si.

Combined Effect of Mg and Ca on Oxidation Behaviors of Zn-Mg Based Alloys Containing a Trace of Ca at High Temperature.

In this study, the combined effect of Mg and Ca on the high temperature oxidation behaviors of Zn-Mg based alloys containing trace Ca was investigated. Phase diagrams for the oxygen partial pressure versus contents of constituent elements were conducted on the basis of thermodynamic calculations to predict oxide scale behavior. Observation of Zn-1/3/5 mass%Mg alloys showed the distribution of a Zn-Zn11Mg2 eutectic phase after primary formation. As-cast microstructures of the Ca-containing alloys included the formation of a Ca-based intermetallic phase. The change in oxidation resistance with variation of the Mg and Ca contents was experimentally examined via thermogravimetric analysis (TGA). The addition of trace Ca led to the formation of Zn13Ca and a CaO/MgO mixed oxide layer on the surface at 460 °C. After TGA at 460 °C under air atmosphere for 1 h, the Ca-free alloys showed rapid weight gain by oxidation, whereas the oxidation resistance of the Ca-added alloys was substantially increased.

Effects of Constituent Phases on Oxidation Kinetics of Al-Mg Alloys Containing a Trace of Ca.

In this study, the effects of constituent phases on the oxidation kinetics of an Al-7 mass%Mg alloy containing a trace of Ca were investigated. A Mg+Al2Ca master alloy was used to add Mg and Ca simultaneously. Scheil-Gulliver cooling by thermodynamic calculation showed that the addition of Ca led to the formation of Ca-based intermetallic compounds, such as Al4Ca and Laves C36, after solidification. Based on weight increase indicated by the oxidation test and surface analysis, it was found that the presence of Ca-based phases significantly improved the oxidation resistance and slowed down the oxidation rates. Based on the review of phase diagrams with oxygen partial pressure by thermodynamic calculation, it was thought that in the initial oxidation, MgO and MgAl2O4 were formed on the surfaces of the Al-Mg alloys, leading to further oxidation. The Ca-based intermetallic compounds formed Ca-Mg-Al based oxides, which possibly contributed to the formation of a relatively dense oxide layer.

Oxidation Kinetics of Cu Alloys Containing Alkaline Earth Metals at Low Temperature.

In this study, the oxidation behavior of Cu alloys containing two alkaline earth metals (i.e., Mg and Ca) at 500 °C was investigated. The Mg+Mg2Ca master alloy was used for the simultaneous addition of Mg and Ca into Cu. As a result of the oxidation test, all examined samples showed weight gains that followed parabolic laws. Mg addition in Cu considerably slowed down the oxidation rate, while the use of the Mg+Mg2Ca master alloy as an alloying element for Mg led to an even further reduction in the oxidation rates at the testing temperature. The phase diagrams with the oxygen partial pressure showed that the Ca and Mg-containing alloy resulted in the formation of CaO as the primary oxide and MgO as the secondary oxide. The improved oxidation resistance can be attributed to the mixed surface layer of CaO and MgO, which control the growth rate of Cu2O.

QUANTIFICATION OF THE KAERI'S MOVABLE NEUTRON IRRADIATOR BY USING A 6LiI(Eu) SCINTILLATOR.

There is no standardised on-site calibration system for performance testing and calibration of neutron area monitors although there is a mobile irradiation device as like a neutron howitzer. For this reason, neutron area monitors, which legally and periodically require calibration in Korea, are removed from the installation location and tested at the Korea Atomic Energy Research Institute (KAERI) or the Korea Research Institute of Standards and Science (KRISS). To test the possibility of an on-site performance calibration system, the KAERI manufactured a movable neutron irradiator. The movable neutron irradiator is composed of high-density polyethylene and has an overall size of 50 cm (L) × 50 cm (W) × 46 cm (H). In this study, the neutron fields generated by the movable neutron irradiator were quantified at distances of 80, 100, 120, and 140 cm from the centre of the source. Quantification was performed using the initially estimated neutron spectrum from the computer simulation, the count rate data measured using a 6LiI(Eu) scintillator combined with a Bonner sphere spectrometer (BSS), and the response function of the BSS. As a result of the quantification of the neutron field at each distance, the fractions of scattered neutrons to total neutron fluence were almost constant within 5%.

Surface Enrichment of Mg and Ca in Cu-Mg Alloy Containing a Trace Amount of Ca and Its Effects on Oxidation Resistance.

In this study, the surface segregation of Mg and Ca in Cu-Mg alloys containing a trace amount of Ca under an oxidative atmosphere and its effects on oxidation resistance were examined. The use of a Mg+Mg2Ca master alloy as an alloying element for Mg rendered significant surface protection during melting and casting. During solid-state oxidation, the oxidation resistance was increased by the addition of Mg. Ca containing alloys with the same Mg exhibited a relatively higher oxidation resistance. From the phase diagram with the oxygen partial pressure as a function of the Mg content, the Ca containing alloy led to the formation of CaO as the primary oxide. The improved oxidation resistance of Ca containing alloys can be attributed to a mixed surface layer of CaO and MgO.

Effect of Ca on Phase Stability and Oxidation Resistance of Al3Mg2 at Elevated Temperature.

In this study, effect of Ca on phase stability and oxidation of Al3Mg2 at elevated temperature was investigated. From thermogravimetric analysis (TGA) at 420 °C, rapid weight gains in the initial stage and incubation were observed for Al3Mg2 and Ca-added Al3Mg2. After incubation for some time, Al3Mg2 sample exhibited the second weight growth, while Ca added sample exhibited continuous incubation during the testing time. The phase diagrams calculated by Factsage 7.1 revealed that Ca exists as Laves_C36 in Al3Mg2 and also forms Ca3MgAl4O10, following formation of MgO and MgAl2O4-spinel as primary and secondary oxides, respectively, on the surface during oxidation at 420 °C.

EVALUATION OF NEUTRON SCATTERING CORRECTION USING THE SEMI-EMPIRICAL METHOD AND THE SHADOW-CONE METHOD FOR THE NEUTRON FIELD OF THE KOREA ATOMIC ENERGY RESEARCH INSTITUTE.

When neutron survey metres are calibrated in neutron fields, the results for room- and air-scattered neutrons vary according to the distance from the source and the size, shape and construction of the neutron calibration room. ISO 8529-2 recommends four approaches for correcting these effects: the shadow-cone method, semi-empirical method, generalised fit method and reduced-fitting method. In this study, neutron scattering effects are evaluated and compared using the shadow-cone and semi-empirical methods for the neutron field of the Korea Atomic Energy Research Institute (KAERI). The neutron field is constructed using a 252Cf neutron source positioned in the centre of the neutron calibration room. To compare the neutron scattering effects using the two correction methods, measurements and simulations are performed using respectively KAERI's Bonner sphere spectrometer (BBS) and Monte Carlo N-Particle code at twenty different positions. Neutron spectra are measured by a europium-activated lithium iodide [6LiI(Eu)] scintillator in combination with the BBS. The calibration factors obtained using each methods show good agreement within 1.1%.

Fast neutron calibration fields constructed using a proton accelerator of KIRAMS and spectrumweighted response of various neutron detectors.

This paper presents the dosimetric quantities, realistic neutron calibration fields and spectrum-weighted response (SWR) of several neutron-measuring devices to provide guidance to health physicists and dosimetry specialists on the proper selection and use of survey meters in neutron fields of varying energy spectra. To yield the SWR, the detector response functions of 17 neutron-measuring devices were numerically folded with each of the produced calibration neutron spectra through the in-house developed software 'K-SWR'. The detectors' response functions were taken from the IAEA Technical Reports Series No. 403. Eight kinds of calibration neutron fields with high energy and high dose rates were produced using a proton accelerator (MC50 cyclotron) of Korea Institute of Radiological and Medical Sciences (KIRAMS). The fluence-average energy (Eave) varied from 3.8 to 16.9 MeV, and the ambient-dose-equivalent rate [H(*)(10) h(-1)] varied from 0.99 to 16.5 mSv h(-1).

Volatile sulfur compounds as a predictor for esophagogastroduodenal mucosal injury.

BACKGROUND/AIMS: Halitosis is a symptom that bothers patients more socially than medically and its pathogenic mechanisms are unclear and treatment armamenterium is limited. Clinicians generally ignored active interventions. Since halitosis is closely associated with volatile sulfur compounds (VSCs), we used a Halimeter and gas chromatography to measure VSCs in patients with Helicobacter-pylori (H. pylori)-associated gastric diseases. METHODS: We categorized 72 patients with H. pylori infection into two groups based on their endoscopic findings: a non-erosive mucosal group (NE, n=24) and an erosive mucosal group (E, n=48). Halitosis was objectively assessed by applying either a Halimeter to breath air or gas chromatography to gastric juice. Simultaneously, the expression of VSC-generating enzyme was measured with reverse-transcriptase PCR using mRNA isolated from biopsy tissues. RESULTS: The levels of VSCs in exhaled breaths or aspirated gastric juices differed significantly between the NE and E groups (p<0.00001), suggesting that VSCs might reflect eroded epithelial damage induced by H. pylori infection. The expressions of cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE) were broadly consistent with the degree of mucosal injury. CONCLUSIONS: Erosive changes in esophagogastroduodenal mucosa were strongly correlated with increased VSC levels, suggesting that halitosis might result from H. pylori-associated erosive lesions.