Evaporation Of Mg Research Articles

Improved wear and corrosion resistance of magnesium AZ80 alloy prepared by laser surface remelting

Laser surface remelting (LSR) is a laser-based surface treatment method. In the LSR process, microstructural defects such as cracks and porosity are suppressed in addition to grain refinement, and the mechanical properties are improved. The present research investigated the effects of LSR parameters on the microstructure, wear, and corrosion behavior of Mg AZ80 alloy. The results showed that in LSR, the coarse-grained (29.8 μm) structure of AZ80 was transformed into a fine-grained structure (3.1 μm) with no microstructural defects. The evaporation of Mg during LSR and the formation of Al-rich and Mg-poor phases are the most important challenges in the surface treatment of AZ80. This limitation was solved by optimizing the LSR parameters, which included a gas flow rate of 2 L min−1, pulse duration of 3 ms, scanning speed of 3 mm s−1, pulse frequency of 8 Hz, and heat input of 64 J mm−1. The prevention of Mg evaporation was associated with the elimination of porosity and cracks, reducing of the solidification range, and uniform distribution of β-Mg17Al12 precipitation phases in α-Mg refined grains. The tribological behavior of the laser-treated region showed that the COF, depth of the wear scar, wear rate, and wear volume loss were reduced by 18%, 48%, 37%, and 66%, respectively, compared to AZ80. This result is attributed to the refinement of α-Mg grains and the uniform distribution of β-Mg17Al12 in the laser-treated region. The results of the polarization curves of the corrosion test in 3.5 wt% NaCl solution showed that the optimal laser-treated region with the lowest corrosion current density (34.68 × 10−6 μA.cm−2) and highest self-corrosion potential (1.425 V) exhibited the highest corrosion resistance. A slight change in the breakdown potential current slope in the laser-treated region indicates the formation of a protective film on the surface after the completion of LSR, which increases corrosion resistance.

Theoretical insights into laser-assisted field evaporation of ionic compounds

This study addresses the kinetic process of field evaporation of MgO assisted by ultrafast laser pulses combining density functional theory and molecular dynamics. A quantitative model is presented to describe the competitive evaporation of Mg and O ions under various conditions by comparing the activation barriers. The coordination number has a significant impact on the evaporation kinetics. The evaporation ratio of Mg to O rises with increasing DC field strength and laser intensity. Moreover, the energetics of evaporation is in correlation with photo-induced field ionization, revealing distinct mechanisms of evaporation for Mg and O. While Mg undergoes further ionization and field evaporation simultaneously, the evaporation of O is coupled with the relaxation of excited carriers. The final charge state of evaporated O is determined by the DC field strength rather than the laser intensity. Our findings provide insights into laser–matter interactions in ionic compounds and contribute to the development of atom probe techniques.

Morphology evolution and mechanism of massive three-level hierarchically porous silver fabricated by vapor phase dealloying

In this study, the Gasar process and vapor phase dealloying (VPD) method were combined to fabricate a massive three-level hierarchical porous silver (MTHPS), which composed of interconnected micron-sized, submicron-sized, and nanoporous structures. The key aspect of this study lies in the preparation of a hypoeutectic Gasar Mg91.6Ag8.4 alloy with the regular micron-scale pore structure as the dealloying precursor, improving the size of the hierarchical porous metal. Under high vacuum conditions, by adjusting the dealloying time and temperature, MTHPS samples with various morphologies were obtained. After dealloying, the MTHPS exhibited Gasar pores (diameter 376 ± 86 μm), submicron pores (diameter 465 ± 125 nm), and a continuous ligament/channel structure (pore size less than 70 ± 40 nm). The coarsening index was 3.6258, and the activation energy was measured to be 0.95 eV, indicating that the formation and coarsening of the pores during VPD are attributed to surface diffusion. The calculated evaporated mass of the precursor alloy after dealloying was very close to the experimental value (±0.004 g), indicating that the evaporation of Mg occurred simultaneously in both solid and liquid phases during the VPD process. This study elucidates the phase transformation characteristics, structural control, and diffusion mechanisms of MTHPS prepared by VPD, providing valuable insights for further research and applications of MTHPS.

Nanoscale liquid Al phase formation through beam heating of MgAl2O4 in TEM.

In this study, electron-beam irradiation of a MgAl2O4 single-crystalline thin-film specimen in a transmission electron microscope reveals an unexpected formation of nanoscale liquid Al droplets. Despite the comparable melting temperatures of Mg and Al, the resulting liquid phase is predominantly composed of Al. This predominant presence of Al in the liquid phase is attributed to the selective evaporation of Mg, driven by its higher vapor pressure at elevated temperatures. Our observations suggest a correlation between electron-beam irradiation and a subsequent rise in specimen temperature. In particular, the observed melting of Al defies explanation by the widely accepted mechanism that attributes specimen heating to electron-energy loss, given the negligible energy deposited as determined by the collision stopping power. Instead, we suggest that the significant specimen heating is due to Auger excitation, a process known to deposit substantial energy. This contention is supported by a quantitative heat-transfer finite element analysis.

Mg Ion Plasma Generated by a High Magnetic Field in a Microwave Resonator

The generation and reduction reaction of magnesium plasma were studied using a cylindrical transverse magnetic-mode applicator in magnetic and electric field modes. By heating Mg powder using the magnetic field mode, plasma was generated with the evaporation of Mg and stably sustained. When the Mg plasma sample was introduced into the reaction zone and exposed to microwave and lamp heating, a reduction reaction of scandium oxide also occurred. The results of this study provide prospects for the development of a larger microwave refining system.

Application of electron beam welding technique for joining coarse-grained and ultrafine-grained plates from Al-Mg-Si alloy

In the present work, the attempt to weld coarse (CG) and ultrafine-grained (UFG) Al-Mg-Si alloy using an electron beam welding technique has been taken. Welding parameters were selected in a way to reduce the energy input, and thus the heat-affected zone (HAZ) and the evaporation of elements with high saturated vapor pressure. The UFG microstructure was beneficial in obtaining smaller grains in the fusion zone (FZ) and HAZ, resulting in higher mechanical strength than weldments from CG Al-Mg-Si alloy. The weld efficiency for CG alloy was 80 %, while for the UFG sample - 68 % (82 %, compared to CG base material). The reasons for a drop in mechanical properties in the FZ were a dissolution of strengthening precipitates and an increase in grain size. Also, the evaporation of Mg (alloying element) and Zn (impurity) occurred to a larger extent. The rupture in both welds occurred in the columnar dendritic area in the FZ, characterized by the elongated dendrites and cube texture that favoured the rupture.

Thermoelectric properties of Mg2Si thin films prepared by thermal evaporation of Mg and face-to-face annealing

Mg2Si thin films were prepared by thermal evaporation of Mg and face-to-face annealing (FTFA) on a crystalline Si substrate and on a P-doped hydrogenated amorphous Si thin films deposited on a quartz substrate. FTFA suppressed the evaporation of Mg, the oxidation of Mg2Si, and the decomposition of Mg2Si. The polycrystalline Mg2Si thin film with a large grain size was obtained. The effects of annealing temperature (TA) during FTFA on crystal structure and thermoelectric properties of Mg2Si thin films were investigated. Raman scattering spectra revealed that Mg2Si was formed by FTFA in the range of TA = 623–923 K, and lower TA led to lower strain and higher crystallinity. From the thermoelectric properties of the sample prepared at TA = 623 K, a relatively high ZT of 0.68 was obtained at 712 K. This ZT was achieved by a drastic increase in electrical conductivity, a relatively high Seebeck coefficient of −235 μV･K−1, and a very low thermal conductivity of 1.4–1.7 W･m−1･K−1.

Selective laser melting of micron-sized niobium functionalized Al7075 alloy: Element evaporation and grain refinement

The broad industrial applications of selective laser melting (SLM) are hindered by the limited printable alloy systems. Among the unprintable alloys, the high-strength Al7075 alloy remains challenging to be processed with SLM due to the formation of hot cracks. In the present work, the inoculation treatment of micron-sized niobium (Nb) powders into Al7075 powders could refine the grains due to the formation of Al3Nb particles, healing cracks by reducing the crack length density. Furthermore, a processing compromise existed between the element evaporation of Mg/Zn and processability during SLM of Al7075 and micron-sized Nb functionalized Al7075 powders. The lower scanning speed, leading to a more severe evaporation of Mg and Zn, could result in a better processability with a lower crack area and length density. The improved printability of SLMed Al7075 with less Mg and Zn content could be explained by the decrease of hot cracking susceptibility. Coupled with the low scanning speed and inoculation treatment of Nb, the as-built Al7075 + 1 vol% Nb alloy could exhibit a low crack length density of 1.29 × 10−5/μm and exhibited a yield strength of 258 ± 13 MPa with an elongation to fracture of 11.1 ± 3.7%. The yield strength and elongation to fracture increased to 283 ± 2 MPa and 16.0 ± 2.8% after the T6 heat treatment. The marginal enhancement of strength is due to the evaporation of strengthening elements of Mg and Zn, lacking precipitation strengthening phase. The compromise among the element evaporation of Mg and Zn, processability, and mechanical properties provided the strategy to balance the printability and mechanical properties during SLM of Al7000 or micron (nano)-functionalized Al7000 series alloys.

Compositional control and high-temperature phase stability of plasma-sprayed Ba(Mg1/3Ta2/3)O3 coatings

The Ba(Mg 1/3 Ta 2/3 )O 3 (BMT) ceramic is considered a promising material for high-performance thermal barrier coating (TBC), due to the ultra-high melting point and excellent thermophysical properties . However, the preferential evaporation of Mg from BMT during plasma spraying causes the composition in deposited coatings to deviate from the standard stoichiometry , resulting in the formation of undesirable barium tantalite. These impurities would accelerate the cracking and failure of BMT with low fracture toughness during thermal shock , which greatly limits the application of BMT coatings. In this study, the evaporation of Mg, and the evolutionary characteristics of the composition and microstructure of BMT particle in the plasma spray process were investigated. The relationship between the melting conditions of BMT particles and the composition and microstructure of the coatings was analyzed. The compositional controls, and the high-temperature phase stability of plasma-sprayed BMT coatings were studied and characterized. The results indicate that the evaporation intensity of Mg was strongly affected by the melting conditions of the BMT particles in the plasma jet . The particles with a higher degree of melting had a greater evaporation intensity of Mg, owing to the higher heat transfer and element diffusion rate, and more impurity phases formed in the deposited coating. The nonuniformity of Mg evaporation in BMT particle could lead to composition segregation, promoting the formation of the impurity phases during particle solidification, and ultimately affect the composition uniformity of the coating. By employing the powder with large particle sizes and adjusting the spray parameters to reduce the energy of plasma jet under the premise of ensuring the coating deposition quality, the evaporation intensity of Mg and the content of impurity phase could be significantly restrained, and the high-temperature phase stability of the coatings could be greatly improved compared to the original unmodified BMT coatings. • Evaporation behavior of Mg in plasma sprayed Ba(Mg 1/3 Ta 2/3 )O 3 (BMT) was investigated. • Relationship between the melting conditions of BMT particles and the characteristics of the coating was analyzed. • The composition of BMT coating was controlled by adjusting the powder size and spraying parameters. • Significant improvement in high-temperature phase stability of the BMT coatings was achieved.

The microstructure and thermoelectric properties of the Mg2(Sn,Si,Bi) films containing excess metal Mg phase

To avoid the uncontrollable Mg content in deposited films caused by the easy evaporation of Mg in alloy target, the Mg2(Sn,Si,Bi) solid solutions films with a tiny of excess Mg metal phase were prepared using a Mg-Sn-Si-Bi alloy target and a high pure Mg target by magnetron sputtering alternately. The phase components, microstructures as well as the thermoelectric properties were systematically investigated. The excess metal Mg phase with a few micron size uniformly distributes in the Mg2(Sn,Si,Bi) solid solution films and the size of the excess metal Mg phase becomes bigger and bigger and the phase gradually convert a narrow strip shape as Mg target sputtering time increase from 40 to 60 s. It is beneficial to an increase in both Seebeck coefficient and electrical conductivity that a tiny excess metal Mg phase exists in Mg2(Sn,Si) based films. The Mg2(Sn,Si) based films containing tiny excess metal Mg phase with an appropriate size posses the highest absolute value of Seebeck coefficient and appropriate electrical conductivity, resulting in the maximum power factor.

Growth, characterization, and stability testing of epitaxial MgO (100) on GaAs (100)

Epitaxial MgO (100) films have been grown on GaAs (100) by evaporation of Mg in the presence of 5 × 10−6 Torr of oxygen. Prior to the growth of MgO, the GaAs (100) substrate was cleaned by Ar ion sputtering and annealing. MgO (100) on GaAs (100) was in situ characterized with Auger electron spectroscopy (AES), and ex situ by scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and energy–dispersive X–ray spectroscopy (EDX). X-ray diffraction patterns indicated that the MgO film has grown predominantly in the cubic phase with the (100) plane parallel to the GaAs (100) substrate. HRTEM results have confirmed the epitaxial growth of MgO with MgO (100)[001]║ GaAs (100)[001]. Despite the high lattice misfit, the epitaxial MgO (100) is grown on GaAs (100) due to the 4: 3 relationship (4 aMgO: 3 aGaAs) between MgO (100) and GaAs (100). The formation of a 4:3 superstructure reduces the lateral misfit between MgO (100) and GaAs (100) to ≈0.65%. To test the potential of MgO as a protection layer for III-V semiconductor based photo-electro catalytic devices for water splitting in alkaline media the reaction of MgO films with H2O and NaOH was investigated. Flake-like Mg(OH)2 structures appear to have formed on top of the MgO films treated with NaOH.

Directed energy deposition of Al 5xxx alloy using Laser Engineered Net Shaping (LENS®)

Here, we present directed energy deposition (DED) of wrought-like Al 5xxx AlMg alloy by Laser Engineered Net Shaping (LENS®). A transition from an Al 5083 gas atomized powder feedstock to Al 5754 characteristics of the as-deposited material due to selective evaporation of Mg was observed. Density values obtained by X-ray micro-computed tomography (μ-CT) were compared to those obtained by the Archimedes method. The latter indicated a relative density as high as 99.26%. Possible origins of porosity are discussed. The as-deposited material was comprised of both equiaxed and columnar grains with no preferred crystallographic orientation and mean grain size of 36 μm. The Young's modulus, yield stress, ultimate tensile strength, fracture strain, Poisson's ratio, and total ultimate strain energy (toughness) were determined by uniaxial tensile tests combined with digital image correlation (DIC). Fractography complemented the mechanical testing. A pulse-echo ultrasonic non-destructive test was used to obtain more accurate values of the Young's and shear moduli and to adjust the value of the yield strength accordingly. The measured mechanical properties meet the requirements of international standards for wrought Al 5754 in its annealed condition.

New deposition method of MgB2 thin film with thermal evaporation of Mg and sputtering of B

We are now developing a new in situ deposition process for MgB2 film as a candidate method to mass-produce MgB2 thin film superconducting tape. In the new method, a MgB2 film is deposited on a heated metal substrate by a hybrid deposition method, which consists of thermal evaporation of magnesium and sputtering of boron. By using the hybrid deposition method, the substrate temperature can raise from 250 to 350 °C, while its fluctuation is kept less than 1 °C, which will improve the quality and reproducibility of MgB2 film in mass production. The Jc of MgB2 film deposited by the hybrid deposition method at 20 K and self-field was more than 30,000 A mm−2, which was better than the results reported by the two-step in situ process using DC sputtering and 830 °C high-temperature post annealing [] or by the as-grown depostion using sputttering targets of Mg and B []. Although we obtained better Jc than other deposition methods that use sputtering process, the Jc is still lower than the value we obtained by using a co-evaporation method with electron beam (EB). We investigated the film structure and Jc–B–T properties of the film made by the hybrid deposition method and compared them with those of the film made by co-evaporation. From the analysis results, we think the reasons for the lower Jc are the larger amount of heterogeneous phases such as magnesium oxides in the film and the amorphous B phase under the MgB2. We expect to improve the the crystal qualities and superconductivities of the MgB2 film deposited by the new method by removing impurities in Ar gas during sputtering and thinning the B amorphous phase by increasing the Mg deposition rate in the initial stage of deposition.

Microstructural, porosity and mechanical properties of lap joint laser welding for 5182 and 6061 dissimilar aluminum alloys under different place configurations

This paper studied the dissimilar aluminum alloys (5082/6061) laser lap welding with different configurations. Two configurations were set up by exchanging the place position of the upper and lower plates under the same parameters. When higher Mg content alloy located as the upper plate, the evaporation of Mg led to the instable welding process and the lower actual heat input, which affected the weld morphology. The solidification microstructures near the fusion line of the two joints were observed by SEM and analyzed by coupling temperature field and phase field method simulation results, longer and wider intergranular liquid channels and more severe solute segregation occurred in 6061/5182 joint. The results validated that 6061/5182 joint had a higher crack sensitivity than 5182/6061 joint. Moreover, crack sensitivity had a greater influence on tensile property than other factors by testing. The two joints presented significantly different porosity and pore morphology. Dense and fine pores appeared when more Mg element content in the upper plate, which related to the failed escape of Mg vapor and the attenuation of laser energy in thickness direction. Moreover, microhardness decreased as Mg element content increasing, because of the dilution effect of the strengthening phases.

The response of heat-treatable filler on non-heat-treatable aluminum alloy substrate against age hardening cycle for intelligent development of surface welded joints using TIG welding process

A more realistic approach is handpicked to scrutinize the weld strength of surface joints using tungsten inert gas welding for repair work. Due to the increased application of non-heat-treatable aluminum alloy (AA5182) in automobile structures, tensile weld strength is tested against heat-treatable filler (AA6061) at three age hardening temperatures (i.e., 170 °C, 200 °C, 230 °C) and times (i.e., 4, 5, 6 h). A convincing increase in peak load value is spotted by increasing the temperature and time, the highest value of 14.06 kN is witnessed at 170 °C and 6 h along with 30.42% improvement in joint strength in contrast to without age hardening state. Comparable high peak load (i.e., 13.89 kN and 13.87 kN) values were also obtained for 200 °C and 230 °C at 4 h but afterward depicted a declining trend at 5 and 6 h. An important macrocharacteristic examination of an inside fused region has represented an area of 42.71% which has comparatively shown a negligible difference of percentage with other specimens. From the regional microstructure perspective, two evidential mechanisms were involved in the strengthening, which includes the adjusted network of grain boundary morphology and the precipitation of Mg2Si which upsurge the growth during age hardening. In addition, the apprehension behind the declining behavior at high temperature is explicatively exemplified from scanning electron microscope micrographs which clinch the coalescence of small voids and the evaporation of Mg from surface as an ultimate reason.

Roles of alloying elements in wetting of SiC by Al

Wetting of SiC by Al alloys is a key issue in the preparation of SiC-reinforced Al matrix composites. The wettability could be improved by alloying of Al, yet controversial results widely exist in the literature. We investigated the effects of four important alloying elements (Si, Cu, Ti and Mg) and their concentrations on the wettability in the Al/SiC system using a dispensed sessile-drop method. The results demonstrate that Si could weaken or even inhibit the formation of Al4C3 and substantially improve the wettability via an adsorption effect; Cu slightly deteriorates the wettability, but alleviates the formation of Al4C3 by decreasing the activity of Al; Ti strongly adsorbs at the solid−liquid interface, forming TiCx instead of Al4C3, and thus significantly improves the wettability; Mg may also favor the wettability due to its help in the disruption of the oxide film covering the Al surface via evaporation and its strong affinity for the silica film on the SiC surface; but for a clean Al/SiC system, the effect of Mg is essentially limited. In addition, the evaporation of Mg always leads to a reduction in the drop volume, which causes a decrease in the apparent contact angle, but this effect is usually neglected.

Improved corrosion resistance of Mg alloy AZ31B induced by selective evaporation of Mg using large pulsed electron beam irradiation

Large pulsed electron beam (LPEB) irradiation was employed as a surface treatment of magnesium (Mg) alloy AZ31B to enhance its corrosion and wear resistance. Selective evaporation of Mg induced by LPEB irradiation at an energy density of 5 J/cm2 for 40 cycles has led to the formation of an Al-enriched re-solidified layer with nano-grained structure consisting of Mg3.1Al0.9 metastable phase. The formation of such a re-solidified layer after LPEB irradiation has enabled a decrease in corrosion rate of Mg alloy AZ31B in 3.5% NaCl solution. Different equivalent electrical circuit models were proposed to account for the corrosion behavior of untreated Mg alloy AZ31B and those subjected to LPEB irradiation. A decrease in wear depth when compared to that of the untreated alloy suggests an increase in wear resistance of LPEB-irradiated Mg alloy AZ31B. Adhesive wear is the predominant mechanism of untreated Mg alloy AZ31B while abrasive wear mechanism dominates for LPEB-irradiated Mg alloy AZ31B.

Control of p- and n-type Conduction in Thermoelectric Non-doped Mg2Si Thin Films Prepared by Sputtering Method

ABSTRACTA method for controlling the conduction-type in Mg2Si films without doping is investigated. Mg2Si films exhibit p-type conduction after a post-heat treatment up to 500 °C in atmospheric He. However, covering the films with Mg ribbon during a subsequent heat treatment at 500 °C converts the conduction to n-type, demonstrating that the heat treatment atmosphere can control the conduction type. Based on the reported first principles calculations suggesting that interstitial Mg and Mg vacancies in Mg2Si are the origins of n-type and p-type conduction, respectively, the post-heat treatment in He induces Mg vacancies due to the evaporation of Mg from the film, resulting in p-type conduction. The subsequent heat treatment when the film is covered with Mg ribbon fills the Mg vacancies and the additional interstitial Mg is incorporated, resulting in n-type conduction. These observations differ from the reported data for heat treatment of stable n-type conduction in non-doped Mg2Si-sintered bodies and may realize a novel control method for the conduction type in Mg2Si films.

Synthesis of MgSiN<sub>2</sub> Powders from the Mg-Si System

Magnesium silicon nitride (MgSiN2) was synthesized without any additives under a nitrogen gas flow (200 mL/min) using a nitriding method. The effects of temperature and holding time on its purity and morphology were investigated. A single-phase MgSiN2 powder was obtained at 1350℃ for 1 h and 1250℃ for 11 h. However, the decomposition of MgSiN2 occurred at 1450℃, suggesting that the optimum temperature for the preparation of MgSiN2 from Mg-Si system was 1350℃. The phase purity, morphology, size of the product and elemental composition of the samples were detected by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy spectrometer (EDS), respectively. The evaporation of Mg and Si resulted in the formation of many voids in the blocky product. The temperature gradient promotes the growth of MgSiN2 on the surface of massive products along the tip. The concentration gradient of Mg and Si vapors in the void resulted in the columnar growth of MgSiN2.

Combined influence of Be and Ca on improving the high-temperature oxidation resistance of the magnesium alloy Mg-9Al-1Zn

The present work showed that the oxidation resistance of Mg-9Al-1Zn at elevated temperatures was improved by combined alloying with Be and Ca. AZ91 alloyed with 20ppm (wt) Be and 0.5wt.% Ca had higher oxidization resistance than that of AZ91 containing 60ppm (wt) Be. The improved oxidation resistance was attributed to (a) the formation of a Be-reinforced compact CaO-MgO composite layer on the alloy surface, and (b) suppressing the grain boundary evaporation of Mg by (i) the elimination of Mg-Al eutectic micro-constituent, and (ii) the increase in thermal stability of the β-Mg17Al12 due to the Ca alloying.