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D H Stjohn - One of the best experts on this subject based on the ideXlab platform.

  • the effect of aluminium content on the eutectic morphology of high pressure die Cast Magnesium aluminium alloys
    Journal of Alloys and Compounds, 2010
    Co-Authors: Matthew S Dargusch, M D Nave, S D Mcdonald, D H Stjohn
    Abstract:

    Increasing aluminium levels in high pressure die Cast Mg-Al alloys results in an increase in the volume fraction of eutectic Mg(17)Al(12) with a change in its morphology from fully divorced through to fibrous. Comparison with work undertaken at slower cooling rates shows that the primary alpha-Mg morphology has a more significant effect on the eutectic Mg(17)Al(12) morphology than cooling rate alone. The morphology of alpha-Mg is controlled by the number of nucleation events and the cooling rate. (C) 2009 Elsevier B.V. All rights reserved.

  • corrosion resistance of aged die Cast Magnesium alloy az91d
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Guangling Song, Amanda L Bowles, D H Stjohn
    Abstract:

    The corrosion behaviour of die Cast Magnesium alloy AZ91D aged at 160 ◦ C was investigated. The corrosion rate of the alloy decreases with ageing time in the initial stages and then increases again at ageing times greater than 45 h. The dependence of the corrosion rate on ageing time can be related to the changes in microstructure and local composition during ageing. Precipitation of the phase (Mg17Al12) occurs exclusively along the grain boundaries during ageing. The phase acts as a barrier, resulting in a decreasing corrosion rate in the initial stages of ageing. In the later stages, the decreasing aluminium content of grains makes the matrix more active, causing an increase in the corrosion rate. Electrochemical testing results also confirm the combined effects of the changes in and phases on the corrosion resistance of the aged die Cast AZ91D alloy. © 2003 Elsevier B.V. All rights reserved.

  • corrosion resistance of aged die Cast Magnesium alloy az91d
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Guangling Song, Amanda L Bowles, D H Stjohn
    Abstract:

    The corrosion behaviour of die Cast Magnesium alloy AZ91D aged at 160 ◦ C was investigated. The corrosion rate of the alloy decreases with ageing time in the initial stages and then increases again at ageing times greater than 45 h. The dependence of the corrosion rate on ageing time can be related to the changes in microstructure and local composition during ageing. Precipitation of the phase (Mg17Al12) occurs exclusively along the grain boundaries during ageing. The phase acts as a barrier, resulting in a decreasing corrosion rate in the initial stages of ageing. In the later stages, the decreasing aluminium content of grains makes the matrix more active, causing an increase in the corrosion rate. Electrochemical testing results also confirm the combined effects of the changes in and phases on the corrosion resistance of the aged die Cast AZ91D alloy. © 2003 Elsevier B.V. All rights reserved.

Tresa M Pollock - One of the best experts on this subject based on the ideXlab platform.

Mark A. Gibson - One of the best experts on this subject based on the ideXlab platform.

  • An A Priori Hot-Tearing Indicator Applied to Die-Cast Magnesium-Rare Earth Alloys
    Metallurgical and Materials Transactions A, 2014
    Co-Authors: Mark A. Easton, Su-ming Zhu, Mark A. Gibson, Trevor B. Abbott
    Abstract:

    Hot-tearing susceptibility is an important consideration for alloy design. Based on a review of previous research, an a priori indicator for the prediction of an alloy’s hot-tearing susceptibility is proposed in this article and is applied to a range of Magnesium-rare earth (RE)-based alloys. The indicator involves taking the integral over the solid fraction/temperature curve between the temperature when feeding becomes restricted (coherency) and that when a three-dimension network of solid is formed (coalescence). The hot-tearing propensity of Mg-RE alloys is found to vary greatly depending on which RE is primarily used, due to the difference in the solidification range. Mg-Nd alloys are the most susceptible to hot tearing, followed by Mg-Ce-based alloys, while Mg-La alloys show almost no hot tearing. The proposed indicator can be well applied to hot-tearing propensity of the Mg-RE alloys. It is expected that the indicator could be used as an estimation of the relative hot-tearing propensity in other alloy systems as well.

  • Heat treatment of vacuum high pressure die Cast Magnesium alloy AZ91
    International Journal of Cast Metals Research, 2013
    Co-Authors: Xiao-jing Wang, Su-ming Zhu, Mark Easton, Mark A. Gibson, Gary Savage
    Abstract:

    Alloys produced by high pressure die Casting (HPDC) are generally considered non-heat treatable because trapped gas pores tend to expand, causing surface blistering and bulk distortion. In this paper, vacuum assisted HPDC of Magnesium alloy AZ91 was used, and the properties were assessed. The specimens produced using vacuum die Casting contain less porosity. Little improvement in yield strength by applying vacuum is found, although a small increase in elongation is observed. A conventional heat treatment applied to the vacuum die Cast AZ91 shows pronounced precipitation hardening during aging, especially after a prior solution treatment. However, an associated improvement in yield strength after aging is not observed, and this is related to the decreased contribution of the ‘skin’ effect as a result of grain growth.

  • electrochemical behaviour and corrosion of mg y alloys
    Corrosion Science, 2011
    Co-Authors: Aaron Sudholz, Mark A. Gibson, Kateryna Gusieva, Xiaobo Chen, Barrington Charles Muddle, Nick Birbilis
    Abstract:

    Corrosion of Cast Magnesium-yttrium (Y) alloys with systematic Y additions up to a nominal 18wt.% were studied. Corrosion performance was related to the quantitative alloy microstructure and found to increase significantly with the level of alloying and volume fraction of the Mg-Y intermetallic present. In the alloy microstructures, Mg24Y5 was principally formed; the electrochemistry of which was characterised using the electrochemical microcell method. Electrochemical testing revealed the fundamental corrosion behaviour of Mg-Y alloys and elucidated the corrosion mechanisms at play. © 2011 Elsevier Ltd.

  • the relationship between microstructure and creep resistance in die Cast Magnesium rare earth alloys
    Scripta Materialia, 2010
    Co-Authors: Su-ming Zhu, Mark A. Gibson, Mark Alan Easton, Jian Nie
    Abstract:

    Abstract Die-Cast Mg–La, Mg–Ce and Mg–Nd binary alloys varying in composition have been used to investigate creep resistance and its relation to microstructure. The remarkable differences in creep resistance observed in these alloys are shown to be related to different levels of rare earth (RE) solute supersaturated in the α-Mg matrix. The results seem to suggest that strengthening of the α-Mg matrix by solid solution and/or precipitation is more important than grain boundary reinforcement by intermetallic phases for the creep resistance of Mg–RE alloys.

I.p. Moreno - One of the best experts on this subject based on the ideXlab platform.

Mingxing Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Grain Coarsening of Cast Magnesium Alloys at High Cooling Rate: A New Observation
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2016
    Co-Authors: Mingxing Zhang
    Abstract:

    Most studies in the area of grain refinement have always taken for granted that higher cooling rate results in finer grains. However, when microstructural variation of the as-Cast Mg with cooling rate was investigated using a specially designed V-shaped copper mold, the results were different. Although fast cooling during solidification led to microstructural refining in pure Mg, grain coarsening was observed at a higher cooling rate in Mg alloys that were inoculation treated with 1.0wt pctZr and 1.4wt pctCaO, and in the Mg-Al binary alloys. It is considered that the grain coarsening at higher cooling rate was attributed to the smaller constitutional undercooling zone formed at fast cooling due to the high temperature gradient in the three Mg alloys. These results can help in redefining the role of cooling rate in the grain refinement process.

  • the influence of cao addition on grain refinement of Cast Magnesium alloys
    Scripta Materialia, 2016
    Co-Authors: Yahia Ali, Dong Qiu, Bin Jiang, Fusheng Pan, Mingxing Zhang
    Abstract:

    CaO was validated as an effective grain refiner for Cast Mg alloys. 0.7 wt.% CaO addition led to significant reduction in grain size. As CaO particles were reproducibly found within the Mg grains, it was considered that CaO particles promoted heterogeneous nucleation. Additionally, some CaO particles were chemically reduced by Mg, which produced Ca solute and contributed to the grain refinement. The present work indicates that co-existence of active nucleants and solutes with high Q-values in the melt is essential to achieve the highest grain refining efficiency. For Mg alloys, chemical reactions should also be considered at inoculation treatment.

  • current research progress in grain refinement of Cast Magnesium alloys a review article
    Journal of Alloys and Compounds, 2015
    Co-Authors: Yahia Ali, Dong Qiu, Bin Jiang, Fusheng Pan, Mingxing Zhang
    Abstract:

    Grain refinement of Cast Magnesium alloys, particularly in Magnesium-aluminium (Mg-Al) based alloys, has been an active research topic in the past two decades, because it has been considered as one of the most effective approaches to simultaneously increase the strength, ductility and formability. The development of new grain refiners was normally based on the theories/models that were established through comprehensive and considerable studies of grain refinement in Cast Al alloys. Generally, grain refinement in Cast Al can be achieved through either inoculation treatment, which is a process of adding, or in situ forming, foreign particles to promote heterogeneous nucleation rate, or restricting grain growth by controlling the constitutional supercooling or both. But, the concrete and tangible grain refinement mechanism in Cast metals is still not fully understood and there are a number of controversies. Therefore, most of the new developed grain refiners for Mg-Al based alloys are not as efficient as the commercially available ones, such as zirconium in non-Al containing Mg alloys. To facilitate the research in grain refinement of Cast Magnesium alloys, this review starts with highlighting the theoretical aspects of grain refinement in Cast metals, followed by reviewing the latest research progress in grain refinement of Magnesium alloys in terms of the solute effect and potent nucleants.