Evaluation of the microstructure and mechanical properties of a new modified cast and laser-melted AA7075 alloy

The mechanical properties and microstructure of as-cast and homogenized AA7075 were investigated. This alloy was modified by adding transition elements 0.3%Sc + 0.5%Zr, 1%Ti + 0.2%B, and 1%Fe + 1%Ni for use in additive manufacturing applications. After adding Ti + B and Sc + Zr, the structure became uniform and finer with the formation of the Al3(Sc, Zr) and TiB2 phases. Coarse structures were obtained with the formation of an extremely unfavorable morphology, close to a needle-like structure when Fe + Ni was added. The mechanical properties of the modified alloys were increased compared to those of the standard alloy, where the best ultimate tensile strength (UTS) and yield strength (YS) were obtained in the AA7075-TiB alloy compared to the standard alloy in as-cast and homogenized conditions, and the highest hardness value was provided by Fe + Ni additives. The effect of the laser melting process on the microstructure and mechanical properties was investigated. Single laser melts were performed on these alloys using 330 V and a scanning speed of 8 mm/s. During the laser melting, the liquation of the alloying elements occurred due to non-equilibrium solidification. A change in the microstructures was observed within the melt zone and heat-affected zone (HAZ). The hardness of the laser-melted zone (LMZ) after adding the modification elements was increased in comparison with that of the standard alloy. Corrosion testing was performed using a solution of 100 mL distilled water, 3.1 g NaCl, and 1 mL HCl over 5, 10, and 30 min and 1 and 2 h. The corrosion resistance of the alloy modified with FeNi was low because of the non-uniform elemental distribution along the LMZ, but in the case of modification with ScZr and TiB, the corrosion resistance was better compared to that of the standard alloy. © 2019 by the authors.Ministry of Science and Higher Education of the Russian FederationThe author (Asmaa M. Khalil) gratefully acknowledges financial support from the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of MISiS (Support project for young research engineers)

Influence of Adding Modifying Elements and Homogenization Annealing on Laser Melting Process of the Modified Alznmgcu with 4%si Alloys

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc + Zr, 4%Si-Ti + B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500◦ C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3 (Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was partially funded by Russian Foundation for Basic Research (RFBR) with project number 19-38-60037

The influence of the modifying elements on the microstructure, mechanical, and deformation properties of aluminum alloys

In the current work, the standard A242 aluminum cast alloy is modified using the stir casting method with titanium (Ti) (0.5% wt.) and boron (B) (0.1% wt.) modifiers. Polarized optical and scanning electron microscopy were utilized to examine the A242 base microstructure, and A242 + TiB modified alloys; the results revealed that the modified A242 + TiB alloy was refined by 13.5 times more than the as-cast alloy. The mechanical properties were investigated experimentally using compression test in addition to the hardness test; the results revealed that the ultimate compressive strength of the A242 + TiB modified alloy was increased by 9.0% more than those of the A242 standard alloy. Moreover, the yield stress was enhanced by 40% at room temperature and 20% at 250 °C. The dynamic properties were studied using a free vibration impact test to study the modifiers’ effect on the dynamic behavior. The grain refinement notably impacted the damping capacity; due to the as-cast inhomogeneity, the conventional alloy A242 exhibited a greater FRF than the modified alloy A242 + TiB. The modified alloy displayed fewer resonance peaks due to grain refinement and excellent intermetallic phase distribution. The simulation process of the investigated alloys was performed using ABAQUS finite element software to predict the deformation behavior under different temperatures. The FE results showed that the modified alloy was more resistant to deformation by 9.1% than the reference alloy, A242, at room temperature and 7.6% at 250 °C, which agreed with the experimental findings

Indoor environment propagation review

A survey of indoor propagation characteristics is presented, including different models for path loss, shadowing and fast fading mechanisms, different channel parameters including signal strength, power delay, coherence bandwidth, Doppler spread and angle of arrival. The concepts of MIMO channels are also covered. The study also explores many types of deterministic channel modelling, such as Finite Difference Time Domain, Finite Integration Method, Ray tracing and the Dominant path model. Electromagnetic properties of building materials, including frequency dependence, are also investigated and several models for propagation through buildings are reviewed

Investigating Physical Exercise among Jordanians with Diabetes Mellitus

Abstract This study is aimed to investigate exercise behaviors (frequency and duration) among Jordanian diabetic patients, and their correlation with their physical characteristics and perceived exercise benefits and barriers, exercise self efficacy, and exercise planning. An exploratory descriptive design was utilized using the cross-sectional survey with self-reported questionnaires (Demographics, Charlson Comorbidity Index, Exercise Self-Efficacy Scale, Exercise Benefits and Barriers Scale, and Commitment to a Plan for Exercise Scale). A convenience sample of 115 Jordanians with diabetes mellitus was recruited from diabetes outpatient clinics. Participants reported an average number of 3.2 physical activities per week (average of 2.9 hours), with walking being the most common activity. Participant's body mass index, comorbidity index, and exercise self-efficacy were correlated with both frequency and duration of exercise (r = −0.393, −0.286, 0.219 and −0.272, 0.383, 0.260, respectively). A predictive model of five predictors (age, BMI, CCI, exercise self efficacy, and perceived exercise barriers) that significantly predicted exercise duration (R 2 = 0.34, F = 9.14, P < 0.000) was found. Diabetic patients were found to exercise less than optimum. Illness itself was not a cause of not exercising compared to lack of time and desire. Factors that can enhance or inhibit participants' engagement in exercise should be included in designing tailored exercise educational programs

Superplasticity of Ti-6Al-4V titanium alloy : microstructure evolution and constitutive modelling

Determining a desirable strain rate-temperature range for superplasticity and elongation-to-failure are critical concerns during the prediction of superplastic forming processes in α + β titanium-based alloys. This paper studies the superplastic deformation behaviour and related microstructural evolution of conventionally processed sheets of Ti-6Al-4V alloy in a strain rate range of 10–5–10–2 s–1 and a temperature range of 750–900 °C. Thermo-Calc calculation and microstructural analysis of the as-annealed samples were done in order to determine the α/β ratio and the grain size of the phases prior to the superplastic deformation. The strain rate ranges, which corresponds to the superplastic behaviour with strain rate sensitivity index m ˃ 0.3, are identified by step-by-step decreasing strain rate tests for various temperatures. Results of the uniaxial isothermal tensile tests at a constant strain rate range of 3 × 10−4–3 × 10−3 s−1 and a temperature range of 800–900 °C are presented and discussed. The experimental stress-strain data are utilized to construct constitutive models, with the purpose of predicting the flow stress behaviour of this alloy. The cross-validation approach is used to examine the predictability of the constructed models. The models exhibit excellent approximation and predictability of the flow behaviour of the studied alloy. Strain-induced changes in the grain structure are investigated by scanning electron microscopy and electron backscattered diffraction. Particular attention is paid to the comparison between the deformation behaviour and the microstructural evolution at 825 °C and 875 °C. Maximum elongation-to-failure of 635% and low residual cavitation were observed after a strain of 1.8 at 1 × 10−3 s−1 and 825 °C. This temperature provides 23 ± 4% β phase and a highly stable grain structure of both phases. The optimum deformation temperature obtained for the studied alloy is 825 °C, which is considered a comparatively low deformation temperature for the studied Ti-6Al-4V alloy

Productivity forecasting of solar distiller integrated with evacuated tubes and external condenser using artificial intelligence model and moth-flame optimizer

This paper aims at developing an artificial intelligence model to forecast the water yield of a modified solar distiller integrated with evacuated tubes and an external condenser. The model consists of a hybrid long short-term memory (LSTM) model optimized by a moth-flame optimizer (MFO) used as a subroutine to obtain the optimal internal parameters of the LSTM model that maximize the forecasting accuracy. The model performance was compared with that of the standalone LSTM model. Both developed models were trained and tested using experimental data of the modified distiller and a conventional distiller. The thermal performance of both distillers is also compared in this article. The maximum daily distillate output achieved for the modified distiller was 3920 l/m2. The forecasted data of both models were compared using several statistical measures. For all measurements, LSTM-MFO outperformed standalone LSTM. The determination coefficient of the forecasted data using LSTM-MFO reached a high value of 0.999 for both solar distillers.The authors extend their appreciation to the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University for funding this work through Research Group no. RG-21-12-03.Scopu

The FIREBIRD Instrument for Relativistic Electrons: Enabling Technologies for a Fast High-Sensitivity, Low-Power Space Weather Radiation Payload

Miniaturized instrument payloads on small satellite and nanosatellite platforms that are deployed in low Earth orbit are demonstrating cost effective weather monitoring platforms with increased temporal and spatial resolution compared to larger weather satellites. The NASA Earth Decadal Survey [1] states that improving the revisit time of microwave radiometers would significantly improve weather forecasting. Radiometers such as the Advanced Technology Microwave Sounder (ATMS) on Suomi National Polar-orbiting Partnership (Suomi-NPP) and the Joint Polar Satellite System-1 (JPSS-1), now NOAA-20, provide an average revisit rate of 7.6 hours; however, a constellation of six CubeSats in three orbital Low Earth Orbit (LEO) planes with microwave radiometers such as the Time-Resolved Observations of Precipitations structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission would provide a refresh rate of better than 60 minutes. In order to effectively use CubeSats in a constellation as a weather monitoring platform, calibration must be used to provide measurements consistent with state of the art measurements, such as ATMS that has a NeDT at 300K of 0.5-3.0K [2]. In this work, we use the Joint Center for Satellite Data Assimilation (JCSDA) Community Radiative Transfer Model (CRTM) to simulate brightness temperatures (https://www.jcsda.noaa.gov/projects_crtm.php), which are used to assess miniaturized microwave radiometer radiometric biases. CRTM is a fast radiative transfer model that uses Fortran functions, structure variables, and coefficient data of the modeled sensor to simulate radiances. The user inputs surface characteristics, scan angles, and atmospheric profiles from sources such as radiosondes, Numerical Weather Prediction (NWP) models, and Global Positioning System Radio Occultation (GPSRO) measurements. The output of CRTM is a simulated brightness temperature that is used to correct radiometric biases in order to meet required instrument NeDT performance. We use radiosonde, GPSRO, and NWP ERA-5 atmospheric profiles in CRTM and compare the results to ATMS brightness temperatures and find an average difference in brightness temperature of 1.95 K, which is comparable to ATMS Integrated Calibration/Validation System (https://www.star.nesdis.noaa.gov/icvs/status_NPP_ATMS.php) reports which show channel bias variations of up to 2 K. We take a similar approach to provide calibration for the Micro-sized Microwave Atmospheric Satellite-2A (MicroMAS-2A), a 3U CubeSat that was launched on January 11th, 2018. MicroMAS-2A carries a 1U 10-channel passive microwave radiometer that provides imagery near 90 and 206 GHz, temperature sounding near 118 GHz, and moisture sounding near 183 GHz. We develop an approach for comparing MicroMas-2A brightness temperatures to radiosonde, GPSRO, and NWP ERA5 atmospheric profiles. Due to the scarcity of GPSRO and radiosonde profiles near the MicroMAS-2A data segments, we determine that NWP models will be the best option for radiance validation. After the next stage of calibration of MicroMAS-2A is completed, we will compare CRTM simulated radiances from ERA profiles to the initial sensor data, with expected results of channel bias variations of \u3c 2 K