Magnesium Alloy Melt Research Articles

Interfacial reaction between AZ91D magnesium alloy melt and mild steel under high temperature

Interfacial reaction between AZ91D magnesium alloy melt and mild steel under high temperature

Influence of slurry delivery rate and height from cooling slope outlet on solidification and structural behaviors of molded AZ91 magnesium alloy

AZ91 magnesium alloy melt experiences partial solidification while flowing on cooling slope with counter flowing water channel underside. It results in continuous production of semisolid slurry available at cooling slope outlet. Current experimental investigations pertain to the influence of slurry delivery rate and slurry delivery height from cooling slope outlet on solidification and structural behaviors (microstructure along with mechanical properties) of AZ91 magnesium alloy intended for semisolid casting. Slurry delivery rate along with slurry delivery height warrant necessary solidification and shear for grain growth and globularization within metal mold for producing semisolid casting. Moderate slurry delivery rate of 0.025 kg/s along with slurry delivery height of 150 mm results fairly modest solidification that would greatly contribute toward enhanced structural behaviors. As, quite smaller/bigger slurry delivery rate/height generate low shear due to slurry flow inertia or accelerated slurry flow resulting stick-slip flow/motion of alloy slurry on cooling slope. It results poorer structural behaviors amid extremely unwanted casting issues. As, throughout the course escape/retain of metal with gas arise. Since, lesser slurry delivery rate/height allows metal to escape thereby reduces strength and vice-versa. Additionally, lesser slurry delivery rate/height allows gas to escape thereby enhances strength and vice-versa. Therefore, moderate cooling slope casting parameter magnitudes guarantee solution to bewilderment.

Investigation on the Atomic Mechanism for Grain Refinement of Magnesium Alloys by Mg-Zr Master Alloy.

The valence electron structure, bond energy, and cohesive energy of Mg, Zr, and α-Mg containing Zr, and α-Zr containing Mg crystals were calculated using the empirical electron theory of solids and molecules (EET). The calculation results show that the bond and cohesive energies of Zr were much greater than those of Mg, so Zr particles could precipitate ahead of α-Mg in general magnesium alloy melts or insoluble Zr particles exist when the magnesium melt temperature is relatively low. The bond energy of α-Zr decreases with the increase in Mg content; therefore, at the end of the growth of Zr particles, the remaining Zr atoms in the melt exist in the form of Mg-Zr clusters. In order to reduce the surface energy of Zr particles, the outer surface of Zr particles tends to terminate with a Zr-Mg atomic layer, that is, a stable two-dimensional Zr-Mg atomic layer is formed first on the (0001) crystal surface of the outermost surface of Zr particles. Furthermore, on the basis of the calculated results, a complementary criterion to the edge-to-edge model of heterogeneous nucleation is also proposed. {ure and single Zr particles cannot become the heterogeneous nucleus of α-Mg, but when there is an atomic layer of two-dimensional Zr-Mg on its surface, the nucleation of particles can be activated. Mg atoms in the liquid phase preferentially attach to the Zr-Mg/Mg-Zr atomic layer on the surface of Zr particles to grow and form a stable ordered structure, which lastly transforms Zr particles into efficient heterogeneous cores.

Purification of AZ80 and Degassing of AZ91 Alloy by Ultrasonic Treatment

The effects of ultrasonic power, treatment time and holding time on AZ80 magnesium melt purification by ultrasonic field were studied. The results indicate that ultrasonic treatment can accelerate the separation of inclusions and attain melt purification. When the magnesium alloy melt is treated with ultrasonic power 80 W at 650 °C for 60 s and holding 100 s, the best melt purification is achieved. Moreover, the effect of ultrasonic degassing on AZ91 alloy was also investigated. When the ultrasonic power is 150 W for 90 s, the hydrogen content and degassing efficiency are 9.6 cm3/100 g and 50.5%, respectively. The corresponding mechanical properties are Rm = 194 MPa, R0.2 = 133 MPa and A = 4.8%, respectively, and the mechanisms of purification and degassing were analyzed because of the cavitation effect.

High temperature wettability and corrosion of ZrO2, Al2O3, Al2O3-C, MgO and MgAlON ceramic substrates by an AZ91 magnesium alloy melt

Wettability and interfacial reactivity of various ceramics (ZrO2, Al2O3, Al2O3-C, MgO, MgAlON) in contact with molten AZ91 were investigated in this paper. MgAlON and Al2O3-C are new materials to be used in magnesium melt filtration, a comparative study of its wettability and corrosion resistance is performed to evaluate their applicability. Modified sessile-drop tests were conducted, measuring contact angles between the ceramic substrates and molten AZ91 droplets at 680 °C; contact surfaces were analyzed by means of scanning electron microscopy. MgAlON showed the largest contact angles, indicating lowest wettability. Al2O3, Al2O3-C, and MgO proved non-wettable as well. Al2O3- and ZrO2-containing substrates underwent noticeable interface reactions with molten AZ91.

Shrinked bifilms in Mg-Gd-Y-Zr alloy

Mg-Gd-Y-Zr alloy has excellent mechanical properties at room and high temperatures, but its high oxidation properties can also result in a significant number of bifilm defects. However, its formation mechanism was not revealed so far, which was explored in the present work. The results showed that the surface oxide film folds into a grid-like double layer structure defect during solidification, due to the difference of thermal expansion coefficient between surface oxide film and matrix. In addition, the oxide film produces microcracks. As the magnesium alloy melt fills the crack, Zr precipitates into crystal nucleus with peritectic reaction and Y2O3 accumulates. These results would shed new lights on the understanding of shrinkage formation of bifilm defects and improving the defects control of magnesium alloy castings.

Preparation and Thermal Properties of BN and LPSO Hybrid Reinforced Magnesium Matrix Composite

Hexagonal boron nitride (h-BN) is a ceramic material with high thermal conductivity (TC) and low coefficient of thermal expansion (CTE), which can improve multiple thermal properties of metal-matrix composites as a reinforcing particle, but its wettability with metal melt is very poor. In order to enhance the wettability between the h-BN and magnesium alloy melt, the electroless plating was used to coat a thin layer of pure nickel on h-BN particles, which was proved to be effective and efficient in this study. The results showed that by adding Y element to magnesium alloy melt to consume Ni element melted from the nickel-plating layer, the long period stacking ordered (LPSO) structure composed of Mg-Ni-Y was successfully formed, and the magnesium matrix composite reinforced by hybrid h-BN and LPSO structure was obtained. After ultrasonic treatment (UT), the TC of the magnesium composite containing 3 vol% h-BN and 14.16 vol% LPSO is 99.92 W/(m·K), which is a 8.3% enhancement compare to the composite without UT. The average CTE (293-373 K) of the composite is 18.36×10-6 K-1, which is reduced by 29.4% compared with pure magnesium.

Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

Herein, the aim is to investigate the applicability of various ceramic foam filter materials in the filtration of magnesium alloy melts. The durability of ceramic foam filters is studied throughout their immersion in an AZ91 melt for up to 60 min at 680 °C. The four selected types of ceramic foam samples consist of ZrO2, uncoated Al2O3‐C and Al2O3‐C coated in MgAlON or Al2O3. Immersion tests are conducted for 5–60 min in a vertical tube furnace in an Ar/SF6 protective atmosphere. After their immersion, the cooled filters are evaluated by means of optical and scanning electron microscopy (SEM). Every filter sample retrieved from the melt is intact; layers of MgO and occasional metal droplets are found on their surfaces, confirming their durability and applicability in the filtration of magnesium melts. The pre‐ and post‐immersion cross sections of the AZ91 samples are evaluated by means of an automatic SEM to assess the presence of inclusions in the metal. The number of inclusions containing oxygen or nitrogen is notably lower for AZ91 samples that were in contact with Al2O3‐C‐, Al2O3‐, or MgAlON‐coated filters, showing the potential of these materials for the filtration of magnesium alloy melts.

Study on Preparation and Properties of Corrosion Resistant 3D Printing Magnesium Alloy Materials

In this paper, the medical magnesium alloy melt containing Mg, Zn, Ca, Nd elements was prepared by liquid forming technology. Through atomization, the medical magnesium alloy powder material for 3D printing was obtained. The microstructure of the alloy was observed by SEM and XRD. The corrosion resistance of the alloy was tested by electrochemistry. The final results show that the 3D printing material of medical magnesium alloy has good structure uniformity and corrosion resistance can be effectively improved by adding Nd element.

Investigation into the Surface Layer Composition Formed on the Ml19 (Mg–Nd–Y–Zn–Zr) Magnesium Alloy during Melting under Protective Gas Atmospheres

The most currently widespread method of flux-free melting of magnesium alloys is melting under a protective gas atmosphere consisting of inert carrier gas with a small additive of active gas. The ML19 (Mg–Nd–Y–Zn–Zr) casting magnesium alloy contains yttrium and neodymium; these metals are rather active. The interaction of similar alloys with protective gas atmospheres is studied poorly and represents considerable practical interest. Sulfur hexafluoride (SF6) strongly affects global warming; therefore, the application of this gas is limited. In connection with this fact, HFC-R134a is used as active gas in several countries. The influence of protective gas mixtures consisting carrier gas (argon or nitrogen) and active gas (SF6 or HFC-R134a) on the composition of protective layer formed on the surface of the ML19 magnesium alloy melt is considered in this work. A special laboratory setup providing the contact of the protective gas mixture with metal during heating, melting, and solidification of the samples, which excluded the influence of surrounding atmosphere, was developed. The loss of alloying elements turned out to be insignificant, but the Y and Nd content in the alloy when applying nitrogen as carrier gas turned out to be lower than when using argon. The zirconium content was lower in alloys melted using SF6 as active gas. The composition and thickness of oxide films forming when using protective atmospheres SF6 and HFC-R134a are similar. The surface film consists mainly of magnesium fluoride (MgF2) with impurities of oxides, fluorides, and nitrides of zirconium, yttrium, and magnesium. The main distinction of the phase composition of the protective film when applying the HFC‑R134a is the presence of a considerable amount of carbon both in the form of compounds and in the free state. It is also established that a thorough dosage of HFC-R134a in protective atmospheres is required because an increase in its fraction in the gas mixture above 1 vol % leads to severe corrosion of the inner crucible surface during melting, which was not observed when using SF6.

Examination of the surface layer composition formed on ML19 magnesium alloy during melting at protective gas atmospheres

Currently the most common method of the magnesium alloys flux free melting is the melting under the gas protective atmosphere. This atmosphere consists of inert carrier gas with low addition of active gas. The ML19 casting magnesium alloy contains Y and Nd that enough active. The interaction of such alloys with gas protective atmospheres is poorly studied and has serious practical importance. Sulfur hexafluoride (SF6) has a great influence on the global warming and because of that its application is limited. As a result, the number of countries cross over to HFC-R134a as the active gas. This paper presents the investigation of the effect of gas protective mixtures consisting of carrier gas (argon of nitrogen) and active gas (SF6 or HFC-134a) on the composition of protective layer formed on the surface of ML19 magnesium alloy melt. It was developed a special laboratory setup providing the contact of the protective gas mixture with the alloy during heating, melting and solidification of the samples and preventing the influence of the surrounding atmosphere. The loss of the alloying elements was negligible but in the case of using nitrogen as a carrier gas the Y and Nd content in alloy was lower than if the argon is used. If SF6 is used as an active gas, the Zr content in alloys was lower. Composition and thickness of oxide film that formed in both SF6 and HFC-R134a protective atmospheres are mostly the same. The surface film is consist of magnesium fluoride (MgF2) with admixtures of oxides, fluorides and nitrides of zirconium, yttrium and magnesium. The key difference of protective layer phase composition if HFC-R134a used as an active gas is presence of the large amount carbon in the form of compounds and in a free state. Additionally, it was established that using of HFC-134a in protective atmosphere requires more careful dosage given the fact of its percentage in the gas mixture of more than 1 vol.% leads to severe corrosion of the crucible inner surface during the melting.

Research status and prospects of melt refining and purification technology of magnesium alloys

Refining and purification is a significant way to obtain pure and high-quality magnesium alloy melts. This paper summarizes the flux refining methods and non-flux purification methods (blowing purification, filtration purification, electromagnetic purification and ultrasonic purification). It also introduces the composite refining technologies that have been widely researched and applied in recent years, including low-voltage pulse electromagnetic technology, ultrasonic argon purification, self-purification technology and non-flux continuous purification technology. Among them, the non-flux continuous purification technology integrates a variety of purification methods, which can produce high-quality magnesium alloy continuously and steadily, realize environmental protection production, and achieve remarkable technical and economic benefits.

Interface reactions of differently coated carbon-bonded alumina filters with an AZ91 magnesium alloy melt

To investigate possible reactions between differently coated carbon-bonded alumina filters and an AZ91 magnesium alloy melt, immersion tests were carried out. Uncoated as well as MgAl2O4-, Al2O3-, nano- (carbon nano tubes/alumina nano sheets) and MgO-C-coated filters were tested. Thermodynamic calculations showed that only magnesia (MgO) and carbon are stable against molten magnesium; alumina (Al2O3) and spinel (MgAl2O4) will be reduced under the formation of magnesia. Optical and scanning electron microscopy as well as EDX analysis were performed near and at the filter-magnesium alloy-interface of the cooled and sectioned filter samples after their immersion into the AZ91 melt. The results of the thermodynamic calculations were confirmed by the experiments. The MgO-C-coated filter was the only one that did not show an in situ-formed layer on its surface after being in contact with the magnesium alloy melt. The alumina- or spinel-containing filter surfaces displayed platelet-like in situ layers after their contact with the molten AZ91. The results of the EDX analysis of these layers suggest their composition of MgO, since notable respective Mg and O contents were detected, as predicted by the calculations.

Fabrication and Characterization of Aligned Carbon Nanotubes Cluster Reinforced Magnesium Composite Based On Ultrasound/Magnetic Compound Field

Abstract Carbon nanotubes (CNTs)-based materials have been the focus of intense research since their discovery because of their superior mechanical properties, good electrical conductivity and unique nano-effect of unique one dimensional nanostructures. Control and manipulation of the alignment of CNTs in the matrix can effectively affect the electrical, optical and mechanical properties of the composites. At present, there are many researches on the magnetic-field induced the alignment of CNTs in the polymer matrix, but less research on magnetic- field induced the alignment of CNTs in the metal matrix. In order to realize the alignment of CNTs in metal matrix, CNTs were firstly magnetically modified by electroless plating, and a uniform layer of cobalt nanoparticles was successfully plated on the surface of carbon nanotubes. For facilitating the macro-analysis of the different factors on the cobalt-carbon nanotubes directional effect, three kinds of matrixes (distilled water, vegetable oil and high viscosity glue) were used to simulate the magnesium alloy melt. The effects of ultrasonic, magnetic field and temperature on the Co coated CNTs dispersion and alignment in three kinds of matrix were studied by orthogonal test. It was found that the dispersion of CNTs was significantly affected by ultrasound and the alignment of CNTs affected by the magnetic field intensity. In this paper, the CNTs / Mg composites were prepared by liquid-state method and the wettability between CNTs and Mg alloy was improved by the modification of carbon nanotubes. Under the compound effect of ultrasonic and magnetic field, the alignment of the carbon nanotubes cluster in magnesium matrix composites was quantitatively characterized by Image J software. It is found that the Cobalt particles coated CNTs can respond well to magnetic field (typically 0.3–0.8T). With the increase of magnetic field strength, CNTs show higher relative frequencies along the magnetic field direction. When the magnetic field strength was 0.8T, the relative frequencies within 20-50° was 0.7. This indicated that Co-CNTs can achieve obviously alignment in AZ91D alloy under a low magnetic field. In addition, the compressive specimens were prepared according to the optimum process parameters determined by the orthogonal test. The compressive properties of the composites parallel to and perpendicular to the direction of the magnetic field were studied. The results shown that the compressive strength of the Co-CNTs/Mg composites was obviously higher than that of the magnesium matrix and exhibited anisotropy due to directional aligned carbon nanotube.

Effects of Blowing Ar on Inclusion and Properties of AZ61 Magnesium Alloy

Magnesium alloys have low density, light weight, strength, stiffness, high heat resistance, good shock absorption, convenient recycling use and other characteristics, which make it have the potential of widely using in aerospace, transportation, weapons, 3C products and other fields. AZ61 magnesium alloy melt was purified by using composite refining technology. The AZ61 micro-structure and mechanical properties were studied after casting, rolling and annealing. Using SF6 and Ar mixed gas to protect melting AZ61 magnesium alloy, the effect was good, and size of inclusion was all blow 50μm. The effect of blowing Ar on inclusion removal was obviously. The inclusion contents were decreased from an initial 1.37% to a final 0.58%. Alloy elongation was increased obviously, which was from an initial 4.02% to a final 7.09%.

The interface bonding mechanism and related mechanical properties of Mg/Al compound materials fabricated by insert molding

To overcome the shortcomings of magnesium alloys such as low strength at an elevated temperature and poor corrosion resistance, the fabrication of Mg/Al compound materials has attracted more and more attention in the recent years. Among the various fabrication methods such as diffusion bonding, friction-stir welding, and fusion welding, insert molding technique has shown some advantages such as low production cost, short processing time and the ability of producing complex shape. However, there are only a few documents about this preparation method. In this paper, the corresponding study is carried out via inserting 6061 aluminum alloy into AZ31 magnesium alloy melt. The interface bonding mechanism and its mechanical behavior are investigated as well. It has been found that a good metallurgical bonding can be formed at the interface, which consists of three layers, i.e., Al3Mg2, Al12Mg17, and Al12Mg17+(Mg) eutectic structure. The average shear strength is 20MPa, which is close to the reported shear strength of the samples prepared by other methods. This research provides a new insight for the fabrication of Mg/Al compound materials.

Fabrication and characterization of closed-cell magnesium-based composite foams

Abstract Closed-cell AZ31 magnesium alloy foams with different percentages of hollow ceramic microspheres (CMs) are synthesized using modified melt foaming method. The distribution of CMs is investigated and also the effect of CMs on the foaming behaviors (specifically for porosity and pore size) and quasi-static compressive behaviors of Mg-based composite foams are characterized. The results show that CMs distribute in cell walls homogeneously and most of them are penetrated by magnesium alloy melt. In addition, the mean pore size declines with the increase of CMs percentage. Moreover, the overall porosity of the foams increases first and then decreases with the increase of CMs content, and the variation tendency is more obvious when the foaming temperature is lower (namely 680 °C). Besides, proper percentage of CMs changes the compression fracture mode of the foams from brittleness to ductility. OM/SEM/EDS/XRD detections and finite element analysis are applied to explain the reasons.

Numerical simulation and experimental validation of SiC nanoparticle distribution in magnesium melts during ultrasonic cavitation based processing of magnesium matrix nanocomposites

A two-dimensional coupled model of the temperature field, flow field and pressure field of SiC nanoparticles reinforced AZ91D magnesium composite slurries fabricated by high-intensity ultrasonic stirring method is established. The multiphase flow mixture model is used to simulate the temperature field, flow field and pressure field of the semi-solid slurries. The effects of ultrasonic stirring parameters on the distribution of SiC nanoparticles in AZ91D magnesium alloy melt are simulated by using finite difference method. The simulation results show that the distribution uniformity of SiC nanoparticles in Mg melts is influenced by ultrasonic power and frequency as well as the ultrasonic processing time and depth of ultrasonic probe dipped into the melts, but the ultrasonic power and frequency have greater influence on particle distribution. In the present work, the magnesium matrix composite with uniform dispersion of SiC nanoparticles can be obtained when the ultrasonic power, the ultrasonic frequency, the depth of ultrasonic probe dipped into the melts and ultrasonic processing time are 2kW, 20kHz, 20–30mm and 120s, respectively. It has been proven that the similar uniform dispersion could be achieved under the optimal ultrasonic processing conditions although SiC particle sizes in the agglomerated SiC-nanoparticles varied between 30nm and 300nm in diameter. Moreover, the microstructure and mechanical properties of the SiC nanoparticles reinforced AZ91D magnesium alloy based composites obtained experimentally are improved significantly by using the optimized ultrasonic processing parameters based on numerical simulation.

Numerical Simulation Research on Wide Casting Nozzle of Twin-Roll Magnesium Alloy

Casting nozzle structure is the decision factor for the formation process of the fluid field of magnesium alloys melt, and the distribution uniformity of the casting nozzle has an important influence on the process stability and the billet quality. In this research, the casting nozzle structures used in producing AZ31 magnesium alloys slab with width of 1500 mm by using horizontal twin-roll continuous casting were taken as research object, and the fluid field of magnesium alloy melt in different casting nozzle structures were simulated, and the influences of the numbers, position, shape and size of the divergent fluid block on the fluid velocity were analyzed. The results show that the fluid velocity distribution obtained by seven divergent fluid blocks were superior to five or three divergent fluid blocks, the streamline divergent fluid blocks were superior to the linear ones, and the small divergent fluid blocks were superior to big ones. At the same time, a new casting nozzle structure was presented, the difference between the maximum and minimum fluid velocity by using the new casting nozzle was 4.69%, and the distribution uniformity of fluid velocity meets the requirement of production.

Review of the Quantitative and Rapid Measurement Technology of Hydrogen in Aluminum and Magnesium Alloy Melt

Pinhole and micro-shrinkage are the ordinary defects founded in the aluminum and magnesium alloy castings,the existence of hydrogen is the main reason for these defaults. So the measurement of hydrogen in aluminum and magnesium alloy melt is an important means to test the degassing effect and to ensure the quality of the melt,and it is significant to improve the casting's quality.With the increasing application of aluminum and magnesium alloy,the development of quantitative and rapid measurement of hydrogen in aluminum and magnesium alloy melt gets more attractive to the metallurgists and foundrymen. The principles,instruments and features of several popular measurement techniques,such as inert gas circulation method,electrochemical method,pressure evaluation method based on Sieviet's law and the method based on acoustic emission,are analyzed and evaluate respectly. It is indicated that those measurement techniques taking high testing speed and low testing cost as main characteristics have a great prospect.