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.

Piezoelectric Nanogenerators Fabricated Using Spin Coating of Poly(vinylidene fluoride) and ZnO Composite.

In this context, the open-circuit voltage generated by either poly (vinylidene fluoride) or PVDF and ZnO composite sample before being enhanced to 4.2 V compared to 1.2 V for the samples of pure PVDF. The spin coating method was used to create a composite film, which served as a piezoelectric nanogenerator (PNG). Zinc oxide (ZnO) nanoparticles and PVDF serve as the matrix for the coating structure. Thin films were created that employed the spin coating method to achieve the desired results of ZnO's non-brittle outcome and piezoelectric characteristics, as well as PVDF for use in self-powered devices. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and fourier transform infrared (FT-IR) were used to evaluate the properties of these formations. The electrical properties of the film were measured using an oscilloscope. Results indicated that by adding ZnO nanoparticles to the PVDF samples, piezoelectric capabilities were enhanced compared to samples containing PVDF only. These results point to promising uses for various wearable devices, such as water strider robot systems and self-operating equipment.

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.

Fabrication of Transparent Superhydrophobic Surface from ZnO Nanorods.

A transparent superhydrophobic surface was fabricated from ZnO nanorods grown on Si and glass substrates in a thermal furnace for industrial applications such as surface coating. Two types of glasses were used for the substrates: slide glass and Corning glass. The ZnO nanorods were then coated with PTFE using existing sputtering technology and then grown on the glasses. The optical transparency and processing temperature of the nanorods on the substrates with and without a ZnO buffer layer were investigated, for comparison. The superhydrophobic surface formed on Corning glass with a 50-nm-thick ZnO buffer layer exhibited a transparency of 80% or higher and a water contact angle of 150° or higher in the visible light region. High optical transmittance of the superhydrophobic surface was achieved by controlling the size and growth direction of the nanorods. X-ray diffraction and scanning electron microscopy images showed that the nanorods on the glass substrates were thicker than those on Si, and the nanorods predominantly grew in the vertical direction on the buffer layer. However, the growth direction did not affect the wettability of the surface. Vertically grown nanorods can still affect optical transmittance because they facilitate the propagation of light. In the case of Corning glass, superhydrophobic surfaces with contact angles of 150° and 152.3° were formed on both samples with buffer layers of 50 nm and 100 nm, respectively. Therefore, a buffer layer thickness in the range of 50-100 nm is suitable for realizing a transparent superhydrophobic surface on a glass substrate.

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%.

Highly Manufacturable Nanoporous Ag Films Using New Sputtering System for Surface Enhanced Raman Scattering Substrate.

We have developed and characterized a highly manufacturable nanoporous Ag film using a custom-made sputtering system for a surface enhanced Raman scattering substrate for biosensors. The Raman response property of the Ag nanoporous thin film peaked at the same characteristic wavelength as a commercial specimen with an intensity that was 1.5 times higher. We also observed the characteristics of the Ag nanoporous films prepared in this study up to 10 picomole of Rhodamine 6G concentration and 1 picomole and 0.1 picomole using additional signal processing methods. The Raman intensity was at least 10 times higher than the intensity of the Ag nanoporous thin film itself, at densities of 4.3 × 104 cps, 4.0 × 104 cps, 2.9 × 104 cps, and 1.4 × 104 cps. The characteristic peak wavelength also differed. The Raman intensity peak was highest at a wave number of 1513/cm, regardless of the thickness of the Ag nanoporous film, and was found to have a large peak, in the order of 1364/cm, 1314/cm, 612/cm, and 1653/cm. Therefore, it can be confirmed that the Ag nanoporous thin film proposed in this paper can be used as a SERS substrate.

Super-Hydrophobic Properties of Aluminum Surfaces Synthesized by a Two-Step Chemical Etching Process.

In this study, super-hydrophobic coatings on Al surfaces were prepared by a two-step chemical etching process using potassium hydroxide and lauric acid as the etching solution and coating solution, respectively. The Al surface was roughened by immersion in potassium hydroxide, and an ethanolic solution of lauric acid was then coated onto the rough Al surface to lower the surface energy. The wettability and surface morphologies of the treated Al surfaces were characterized using contact angle measurement and scanning electron microscopy, respectively. Microstructures were formed on the treated Al surfaces, which increased the contact angle of the surface (>150°). The contact angle hysteresis was measured between 2.7° and 3° on average, indicating that the surface energy of the Al substrate was low, and the lauric acid was uniformly coated on the substrate. This super-hydrophobic coating showed excellent self-cleaning and corrosion-resistant behavior. The coated samples floated on the water surface and demonstrated excellent water repellent properties. In addition, the coatings were mechanically stable and had an excellent regeneration ability, as verified experimentally. The lauric acid used to lower the surface energy is considered more environment-friendly and more durable than the widely used polytetrafluoroethylene (PTFE).

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.

Transparent and Conducting Oxide Films: SiO2-Doped ZnO.

(SiO2)x(ZnO)100-x films with x = 2, 3, 4, and 5 wt.% were deposited on slide glass substrates at room temperature by the conventional Rf magnetron sputtering method. Their resistivities were investigated as a function of SiO2 content. The lowest resistivity of 4.5×10-3 Ω.· cm was obtained for the (SiO2)x(ZnO)100-x film with x = 2 wt.%. This film showed an excellent average transmittance of 85% in the visible range with a wide band gap over 3.4 eV and a high refractive index of 2.1. In addition, the electrical conductivity of the films was improved by annealing at a temperature films decrease range from 100 °C to 400 °C in vacuum. The resistivities of (SiO2)x(ZnO)100-x with increasing annealing temperature. In particular, SZO film with x = 2 wt.% shows a minimum resistivity of ~10-3 Ω.cm after the heat treatment for 30 min at 300 °C in vacuum. Thus, we suggest that (SiO2)x(ZnO)100-x films being sufficiently transparent and having a high conductivity, are suitable for application as transparent and conductive oxide films.

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%.

Combined Effects of Pyramid-Like Structures and Antireflection Coating on Si Solar Cell Efficiency.

We developed a novel process for synthesizing Si solar cells with improved efficiencies. The process involved the formation of pyramid-like structures on the Si substrate and the deposition and subsequent thermal annealing of an antireflection coating. The process consisted of three main stages. First, pyramid-like structures were textured on the Si substrate by reactive ion etching and subsequently etched using a mixture of HF, HNO3, and deionized water for 300 s. Next, an antireflection coating was deposited on the substrate and was subsequently thermally annealed in a furnace in a N2 atmosphere. After the annealing process, the minority carrier lifetime increased by approximately 40 µs. Further, because of the increase in the minority carrier lifetime and the uniform doping of the substrate, the leakage current decreased. As a result, the efficiency of resulting solar cell increased to 17.24%, in contrast to that of the reference cell, which was only 15.89%. Thus, uniform doping and the thermal annealing of the antireflective coating improved solar cell efficiency.