Molten AZ91 Research Articles

Effect of Ca and rotation speed on microstructure and solidification parameters of AZ91 magnesium alloy produced by semi-solid casting through rotating container process

Microstructure of AZ91 magnesium alloy was modified by using semi-solid rotating container process (RCP) and addition of 1 wt.% Ca. Thermal analysis (CA-CCTA) was performed during semi-solid process in order to determine the relationship between microstructural modification and RCP parameters. The container containing molten AZ91 alloy was rotated by rotation speed of 0, 150, 180 and 210 r/min at 640−580 °C. The cooling curves were plotted to determine the solidification characteristics, solid fraction and dendrite coherency point (DCP). The results indicated that the cooling rate increased with increasing the rotation speed significantly and led to an increase in maximum solidification range of 15.9 and 6.4 °C for AZ91 and AZ91−1Ca (wt.%), respectively. Applying shear force to the slurry at 180 r/min minimized the solid fraction and delayed appearance of DCP. It affected the microstructure characteristics such as grain size and circularity factor. The rotation of 180 r/min at 585 °C resulted in the globular microstructure with a circularity factor of 0.72 and a grain size of 73.4 μm. The addition of 1 wt.% Ca to AZ91 in the optimum condition of RCP increased the circularity factor to 0.81 and reduced the grain size to 53.2 μm.

Enhancement of wettability in AZ91/B4C system by a mechanical purification of liquid alloy

Mg-based alloys are potential candidate materials for a fabrication of lightweight boron carbide based composites through a reactive melt infiltration approach. In this paper, the effect of a mechanical purification of molten AZ91 alloy's surface on its wettability with polycrystalline B 4 C is experimentally evaluated for the first time. For this purpose, sessile drop experiments were performed under the same operating conditions (700 °C/5 min; Ar atmosphere), by using both the classical contact heating (CH) and the improved capillary purification (CP) procedure. It was found that the evolution of contact angle values was strongly influenced by the applied procedure. In particular, by using the classical CH procedure, the presence of a native oxide layer on the metal surface hinders the observations of melting process, resulting in a misleading conclusion that the system is non-wettable. Contrarily, during the wetting test performed by applying the CP procedure, the surface oxide layer was mechanically removed by squeezing the molten AZ91 alloy through a capillary. Accordingly, the oxide-free AZ91 drop with a regular and spherical shape was successfully obtained and dispensed on the B 4 C substrate. A reliable contact angle value of θ =83° was measured at the AZ91/B 4 C triple line at 700 °C, which in turn proves that B 4 C is wetted by the liquid AZ91 alloy. In contradiction to the literature, these good wetting conditions were assisted by a non-reactive wetting mechanism occurring at the AZ91/B 4 C interface. To succeed in the fabrication of AZ91/B 4 C composites by liquid metal infiltration, such experimental observations make it reasonable to expect a spontaneous infiltration process exclusively driven by capillarity, which in turn increases the efficiency of the process by the absence of reaction products that could be a potentially detrimental factor.

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.

Complex reaction behaviour of ceramic mould with the molten AZ91 alloy during investment casting

The effects of different pouring temperatures on the reaction behaviour of the ceramic shell with the molten Mg-9%Al-1%Zn-0.4%Mn (all are in wt-%) (AZ91) alloy during investment casting were studied. The scanning electron microscopy (SEM) micrographs with energy dispersive spectroscopy (EDS) analysis illustrated a complex interaction behaviour of the alloy with the mould components at various pouring temperatures. The MgO + MgAl2O4 compounds were formed on the surface of investment cast alloy at the pouring temperature of 600°C. With increasing the temperature to 650°C, the MgO compounds with the Al2O3 particles were observed at the interface of metal/mould. The Al2O3 particles were the main compound on the surface of alloy at the pouring temperature of 700°C. The formation of Al2O3 particles instead of the MgO compounds on the surface was related to the increase of magnesium evaporation by enhancement of the pouring temperature and also diffusion of Al2O3 particles from the ceramic shell to the surface of the alloy.

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.

Analysis of interface between components in AZ91 magnesium alloy foam composite with Ni-P coated fly ash cenospheres

The interface between the components in magnesium matrix foam composites with fly ash cenospheres has been analysed. The composite based on AZ91 commercial magnesium alloy with hollow aluminosilicate cenospheres was fabricated by the negative pressure infiltration technique. Ni-P coated cenospheres heated to 773 K were used in this study. Analyses of the composite microstructure were carried out by light microscopy, XRD, scanning and transmission electron microscopy. The fabricated composite was characterized by uniform distribution of cenospheres free from damage and unfilled by the AZ91 alloy within the matrix. Analyses of the composite matrix microstructure revealed that it was composed of α-Mg, α+γ divorced eutectic, γ discontinuous precipitates and an Al8Mn5 intermetallic phase. Examinations of the composite interfaces disclosed that Ni3P and Ni phases were formed inside the Ni-P coatings during heating of the cenospheres. Additionally, NiO was created in the external layer of the Ni-P coatings due to the oxidation reaction. The presented results unequivocally revealed that the used Ni-P coating, especially the NiO layer, on the cenospheres prevent reactions between the molten AZ91 alloy and fly ashes.

Microstructure of the Bonding Zone Between AZ91 and AlSi17 Formed by Compound Casting

AbstractThis paper discusses the joining of AZ91 magnesium alloy with AlSi17 aluminium alloy by compound casting. Molten AZ91 was cast at 650°C onto a solid AlSi17 insert placed in a steel mould under normal atmospheric conditions. Before casting, the mould with the insert inside was heated up to about 370°C. The bonding zone forming between the two alloys because of diffusion had a multiphase structure and a thickness of about 200 μm. The microstructure and composition of the bonding zone were analysed using optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the bonding zone adjacent to the AlSi17 alloy was composed of an Al3Mg2intermetallic phase with not fully consumed primary Si particles, surrounded by a rim of an Mg2Si intermetallic phase and fine Mg2Si particles. The bonding zone near the AZ91 alloy was composed of a eutectic (an Mg17Al12intermetallic phase and a solid solution of Al and Si in Mg). It was also found that the compound casting process slightly affected the AZ91 alloy microstructure; a thin layer adjacent to the bonding zone of the alloy was enriched with aluminium.

AZ91 Magnesium Alloy/Porous Hydroxyapatite Composite for Potential Application in Bone Repair

AZ91/HA composite was prepared by AZ91 magnesium alloy and porous HA using squeeze casting method. The microstructure and mechanical property of the AZ91/HA composite were studied. The results show that the molten AZ91 alloy completely infiltrated the preform without destroying the porous structure of the HA preform. The compressive strength of AZ91/HA composite increased significantly compared with that of the porous HA. The immersion test indicated that AZ91 alloy shows a lower corrosion resistance and is easier to be corroded in comparison with HA.

Hybrid Processing of AZ91 Magnesium Alloy/Nano-Al<sub>2</sub>O<sub>3</sub> Composites

In the present work mechanical and wear behaviour of AZ91 magnesium alloy based composites, reinforced with nanoAl2O3 particles is studied. The composites with different amount of alumina particles are fabricated by a hybrid processing approach. The hybrid processing involved alumina particles dispersion in molten AZ91 alloy by mechanical stirring assisted with ultrasonic processing. Dry sliding wear tests are performed using a pin on disc apparatus against hardened steel at loads ranging from 4.9 N to 14.7 N. The microstructural investigation revealed that, a refined microstructure is obtained because of the heterogeneous nucleation induced by ultrasonic processing and nanoAl2O3 dispersion. Hardness, yield strength and maximum compressive stress of the nanocomposites are found to be superior to that of the matrix alloy. The resistance against wear is increased due to incorporation of reinforced nanoAl2O3particles. The wear rate of nanocomposite is decreased with increasing the amount of the reinforcement. The identified wear mechanisms are abrasion and oxidation.

Understanding the reaction mechanism of in-situ synthesized (TiC–TiB2)/AZ91 magnesium matrix composites

Magnesium matrix composites reinforced with a network of TiC and TiB2 compounds have been successfully synthesized via an in-situ reactive infiltration technique. In this process, the ceramic reinforcing phases, TiC and TiB2, were synthesized in-situ from the starting powders of Ti and B4C without any addition of a third metal powder such as Al. The molten AZ91 magnesium alloy infiltrates the preform of 3Ti–B4C by capillary forces. Furthermore, adding different weight percentages of MgH2 powder to the 3Ti–B4C preforms was used in an attempt to increase the Mg content in the fabricated composites. The results reveal a relatively uniform distribution of the reinforcing phases in the magnesium matrix with very small amounts of residual Ti, boron carbide and intermediate phases when they are fabricated at 900 °C for 1.5 h using a 3Ti–B4C preform with 70% relative density. On the other hand, after adding MgH2 to the 3Ti–B4C preform, TiCx and TiB2 formed completely without any residual intermediate phases with the formation of the ternary compound (Ti2AlC) at the expense of TiC. The percentage of reinforcing phases can be tailored by controlling the weight percentages of MgH2 powder added to the 3Ti–B4C preform. The results of the in-situ reaction mechanism investigation of the Ti–B4C and Mg–B4C systems show that the molten magnesium not only infiltrates through the 3Ti–B4C preform and thus densifies the fabricated composite as a matrix metal, but also acts as an intermediary making the reaction possible at a lower temperature than that required for solid-state reaction between Ti and B4C and accelerates the reaction rate. The investigation of the in-situ reaction mechanism with or without the addition of MgH2 powder to the 3Ti–B4C preforms reveals similar mechanisms. However, the presence of the MgH2 in the preform accelerates the reaction resulting in a shorter processing time for the same temperatures.

Effect of ultrasonic vibration and solution heat treatment on microstructures and tensile properties of AZ91 alloy

Abstract Ultrasonic vibration with frequency of about 20 kHz and power of 350 W was introduced into molten AZ91 alloy. After ultrasonic vibration, morphology of the phase Mg17Al12 formed during the cooling and solidification varied from coarse plates to lamellar precipitates. With application of solution heat treatment, the phase Mg17Al12 was mostly dissolved in both the alloy with ultrasonic vibration and without ultrasonic vibration. The ultimate tensile strength and the elongation to fracture of the alloy were significantly increased after ultrasonic vibration. After solution heat treatment the tensile strength of the alloy without ultrasonic vibration increased remarkably while the alloy with ultrasonic vibration increased slightly.

Fabrication and characterisation of AZ91/SiC composite by pressureless infiltration method

Since the spontaneous infiltration of molten AZ91 Mg alloy into the powder bed containing SiC particles occurred at 700°C for 1 h under a nitrogen atmosphere, it was possible to fabricate Mg alloy composites reinforced with SiC particles. Since the fabrication conditions (e.g. temperature, time and atmosphere) of the composite are different from those of the other fabrication route, reaction products formed during the composite fabrication were investigated in detail using field emission scanning electron microscopy and high resolution transmission electron microscopy. From the analysis of reaction products, the authors can identify the formation of MgO, MgAl2O4, Al12Mg17 and an AlN phase containing magnesium.

Effects of Ultrasound Power on Microstructure and Mechanical Properties of AZ91 Alloy

Ultrasonic vibration was introduced into the molten AZ91 alloy in this paper. The effects of ultrasound power (from 0 to 900W) on the microstructure and mechanical properties of AZ91 alloy were investigated. The results show that the microstructure, hardness and mechanical properties of the AZ91 alloy have been improved with the ultrasonic treatment. In this work, the mechanical properties of the alloy reached the peak value when the ultrasound power was 600W. Also, the mechanism of ultrasonic vibration in the AZ91 alloy was discussed.

Characteristic reaction products in the AZ91/SiC composite fabricated by pressureless infiltration technique

Since the spontaneous infiltration of molten AZ91 Mg alloy into a powder bed containing SiC particles occurred at 700 °C for 1 h under a nitrogen atmosphere, it was possible to fabricate Mg alloy composites reinforced with SiC particles. Since the fabrication conditions (e.g. temperature, time, and atmosphere) of the composite are different from those of the other fabrication route, reaction products formed during the composite fabrication were investigated in detail using field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HRTEM). From the analysis results, we could identify the formation of MgAl2O4 and AlN, as well as MgO in fabricated composite.

Characterization of protective oxide layers formed on molten AZ91 alloy containing Ca and Be

AZ91 alloy in its molten state oxidizes rapidly in atmospheric conditions and begin to burn from the melt surface. In order to prevent the molten AZ91 alloy from burning, it is usually protected by a cover gas such as sulfur hexafluoride (SF6). However, the use of SF6 gas poses a serious threat to the environment as it is widely acknowledged to contribute to the global warming effect. Thus, several types of studies aimed at controlling the oxidation behavior of molten magnesium alloys have been carried out. This paper describes the characteristics of the oxide layers formed on molten AZ91 alloys containing Ca and Be. The surface analysis technique of GDS (Glow Discharge Spectroscopy) was used to investigate the oxide layers of AZ91 alloys containing Ca and Be. The GDS results showed that the oxide layer consists of CaO, MgO, BeO and Al2O3.

Observation of Manganese-Bearing Particles in Molten AZ91 Magnesium Alloy by Rapid Solidification

Magnesium alloy AZ91 contains 0.1 to 0.3 mass% manganese as an alloying element. Such manganese always reacts with aluminum and produces various compounds. Actually, numerous Mn-bearing particles are visible in polished surfaces under an optical microscope. Some Mn-bearing particles are also expected to be present in molten alloy. We believe that some Mn–Al compounds are closely related to the superheating effect. However, it is not clear specifically what compounds exist in molten alloy and how contribute to grain refinement by superheating. In order to study this subject, we utilized a diffusionless process based on rapid solidification. Two grams of AZ91 alloy was melted in a stainless steel tube and then injected onto a copper wheel rotating at high-speed under various conditions to obtain cast ribbons. Cast ribbon was analyzed by an X-ray diffractometer, an electron probe micro-analyzer and a transmission electron microscope. These analyses indicated that the cast ribbons consist of single phase and that the structure is quite homogeneous, i.e., diffusionless solidification occurs due to rapid cooling. Manganese-bearing particles completely disappear in the melt around 963 K and superheat temperatures, which is inconsistent with presently accepted superheat mechanisms, the temperature-solubility nucleation theory and the temperature-phase relationship theory. In the meantime, cross-shaped Mn-bearing particles are often observed in the ribbons when the melt is cooled from superheat temperatures to the injecting temperature (973 K) before injecting. This treatment may facilitate the formation of these particles.

ＡＺ９１マグネシウム合金の結晶粒微細化に及ぼす炭素粉末添加効果

Grain refinement of cast magnesium alloys containing Al is attained by adding carbon materials. This technique is well established. However, it is important problem that C2Cl6 as grain refiner generates dioxin matters. Therefore, it is impossible to use grain refiners containing chloride. This study was performed to develop a new grain refiner containing C element instead of harmful C2Cl6. Carbon is an important element for grain refining of the commercial AZ91 magnesium alloy. Pure carbon (99.9%) powder with high-purity argon gas carrier was blown into the molten AZ91 magnesium alloy. Fine grains were obtained by addition of the carbon powder. Foreign substances as nucleants could be observed in the center of each grain. The result of EPMA analysis indicated that the foreign substance was consisted of Al, C and O.

Clarification of Grain Refining Mechanisms of Superheat-Treated Mg-Al-Zn Alloy Castings

We performed two experiments to clarify the grain-refining mechanisms of Mg-Al system alloys by superheat treatment of molten alloys. Numerous Al 4 C 3 nucleants were formed in the molten commercial-purity alloy of AZ91 by superheat treatment. The high-purity alloy was made of 99.99% Mg and 99.999% Al. Grain refinement occurred without superheat treatment. A small amount of impurity carbon included in the pure Mg and Al reacted with Al to form Al 4 C 3 compounds. Carbon is an important element for grain refining of commercial-purity AZ91 alloy. Pure carbon powder with an argon gas carrier was therefore blown into the molten AZ91 alloy instead of harmful C 2 Cl 6 . Numerous Al 4 C 3 nucleants were formed in the molten alloy.

Citizenship Laboratory

Previous articleNext article No AccessCitizenship LaboratoryRaymond NelsonRaymond Nelson Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 56, Number 3Mar., 1948 Article DOIhttps://doi.org/10.1086/441487 Views: 1Total views on this site Citations: 7Citations are reported from Crossref Journal History This article was published in The School Review (1893-1979), which is continued by the American Journal of Education (1979-present). PDF download Crossref reports the following articles citing this article:Yosuke Tamura, Jiro Yagi, Tadashi Haitani, Tetsuichi Motegi, Norio Kono, Hiroshi Tamehiro, Hideo Saito Observation of Manganese-Bearing Particles in Molten AZ91 Magnesium Alloy by Rapid Solidification, MATERIALS TRANSACTIONS 44, no.44 (Jan 2003): 552–557.https://doi.org/10.2320/matertrans.44.552Tadashi HAITANI, Yosuke TAMURA, Eiji YANO, Tetsuichi MOTEGI, Norio KONO, Eiichiro SATO Gram refining mechanism of high purity Mg-9 mass%Al alloy ingot and influence of Fe or Mn addition on cast grain size., Journal of Japan Institute of Light Metals 51, no.88 (Jan 2001): 403–408.https://doi.org/10.2464/jilm.51.403Eiji YANO, Yousuke TAMURA, Tetsuichi MOTEGI, Eiichiro SATO Grain refining mechanism of cast magnesium alloy AZ91 by superheat treatment., Journal of Japan Institute of Light Metals 51, no.1111 (Jan 2001): 594–598.https://doi.org/10.2464/jilm.51.594Yousuke TAMURA, Norio KONO, Tetsuichi MOTEGI, Eiichiro SATO Grain refinement of cast Mg-Al alloys., Journal of Japan Institute of Light Metals 48, no.88 (Jan 1998): 395–399.https://doi.org/10.2464/jilm.48.395Yousuke TAMURA, Norio KONO, Tetsuichi MOTEGI, Eiichiro SATO Grain refining of pure magnesium by adding Mg-Zr master alloy., Journal of Japan Institute of Light Metals 47, no.1212 (Jan 1997): 679–684.https://doi.org/10.2464/jilm.47.679J. Minor Gwynn Chapter I: Philosophy, Goals, and Social Factors, Review of Educational Research 21, no.33 (Jun 2016): 173–185.https://doi.org/10.3102/00346543021003173Henry J. Otto, Mary Clare Petty Chapter IV: Internal Organization of Schools and School Systems, Review of Educational Research 19, no.44 (Jun 2016): 301–310.https://doi.org/10.3102/00346543019004301