The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
David H. Stjohn - One of the best experts on this subject based on the ideXlab platform.
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Essential Readings in Magnesium Technology - Grain Refinement of magnesium
Essential Readings in Magnesium Technology, 2016Co-Authors: Young C. Lee, Arne K. Dahle, David H. StjohnAbstract:Grain formation during solidification of magnesium and Mg-Al alloys has been studied with a focus on Grain Refinement mechanisms, solute and particle effects. The variation in Grain size with increased aluminium content in hypoeutectic Mg-Al alloys showed a continuous decrease in Grain size up to 5 wt% Al, and a stabilisation at higher Al contents (above 5 wt%). Strontium additions to both low- and high-aluminium content magnesium alloys showed that Sr had a significant Grain refining effect in low-aluminium containing alloys. However, strontium had a negligible effect on Grain size in the Mg-9Al alloy. Additions of Zr, Si, or Ca to pure magnesium produced significant Grain Refinement, probably because these elements have high growth restriction effects during solidification. An attempt was made to identify the Grain Refinement effect of particles added directly to the melt that are considered to be powerful nucleants in Al based alloys (TiC) and in Mg based alloys (AlN, Al4C3). Most of these particles produced Grain Refinement, probably because of enhanced nucleation due to the small lattice disregistry between their crystal structures and that of magnesium. However, it is not clear whether the Grain refining mechanism of the effective particles was catalysis of primary crystal nucleation or simply restriction of crystal growth during solidification.
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Grain Refinement in alloys: Novel approaches
Encyclopedia of Materials: Science and Technology, 2011Co-Authors: Mark Alan Easton, Ma Qian, David H. StjohnAbstract:Grain Refinement is used in many castings to reduce defects and improve processability and properties. This article explains that Grain Refinement can be understood as being due to an interdependent relationship between nucleation and growth, where growth is primarily controlled by the addition of alloying elements. Models for nucleation are discussed including the role of particle size and the recent epitaxial nucleation theory. Methods for Grain refining alloys including the production of semi-solid billet through control of processing parameters and external treatments such as ultrasonication and pulsed magneto-oscillation are also presented.
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A new analytical approach to reveal the mechanisms of Grain Refinement
Advanced Engineering Materials, 2007Co-Authors: David H. Stjohn, Peng Cao, Ma Qian, Mark Alan EastonAbstract:This paper presents an overview of a new methodology for investigating the Grain Refinement performance of alloys and master alloys and then uses this methodology to shed new light on the mechanisms occurring during superheating and native Grain Refinement, and the effect of iron and manganese on Grain Refinement in magnesium alloys. The methodology also describes changes in Grain size upon Zr Grain Refinement of Mg and has been used to analyse the potential for the use of SiC to Grain refine Mg-Al alloys. With this new methodology, and the knowledge it generates, the potential for the discovery of new or improved refiners is significantly enhanced.
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Mechanism for Grain Refinement of magnesium alloys by superheating
Scripta Materialia, 2007Co-Authors: Peng Cao, Ma Qian, David H. StjohnAbstract:The mechanisms for Grain Refinement of magnesium alloys by superheating have remained ambiguous since 1931. A model has been proposed on the basis of the recent understanding of the Grain Refinement of both high purity and commercial purity Mg–Al alloys. The model explains most of the experimental observations about superheating. Analysis of the Grain size data obtained from different Mg–Al alloys as a function of the growth restriction factor with and without superheating provides good support to the model.
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Grain Refinement of magnesium alloys
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: David H. Stjohn, Peng Cao, Ma Qian, Mark Alan Easton, Zoe HildebrandAbstract:The literature on Grain Refinement of magnesium alloys is reviewed with regard to two broad groups of alloys: alloys that contain aluminum and alloys that do not contain aluminum. The alloys that are free of aluminum are generally very well refined by Zr master alloys. On the other hand, the understanding of Grain Refinement in aluminum bearing alloys is poor and in many cases confusing probably due to the interaction between impurity elements and aluminum in affecting the potency of nucleant particles. A Grain Refinement model that was developed for aluminum alloys is presented, which takes into account both alloy chemistry and nucleant particle potency. This model is applied to experimental data for a range of magnesium alloys. It is shown that by using this analytical approach, new information on the Refinement of magnesium alloys is obtained as well as providing a method of characterizing the effectiveness of new refiners. The new information revealed by the model has identified new directions for further research. Future research needs to focus on gaining a better understanding of the detailed mechanisms by which Refinement occurs and gathering data to improve our ability to predict Grain Refinement for particular combinations of alloy and impurity chemistry and nucleant particles.
Ming-xing Zhang - One of the best experts on this subject based on the ideXlab platform.
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current research progress in Grain Refinement of cast magnesium alloys a review article
Journal of Alloys and Compounds, 2015Co-Authors: Yahia Ali, Dong Qiu, Bin Jiang, Fusheng Pan, Ming-xing ZhangAbstract: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.
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the Grain Refinement mechanism of cast aluminium by zirconium
Acta Materialia, 2013Co-Authors: Feng Wang, Mark Alan Easton, Zhilin Liu, Dong Qiu, J A Taylor, Ming-xing ZhangAbstract:Abstract The mechanism underlying the Grain Refinement of cast aluminium by zirconium has been studied through examination of a range of Al alloys with increasing Zr contents. Pro-peritectic Al 3 Zr particles are reproducibly identified at or near the Grain centres in Grain-refined alloy samples based on the observations of optical microscopy, scanning electron microscopy and X-ray diffraction. From the crystallographic study using the edge-to-edge matching model, electron backscatter diffraction and transmission electron microscopy, it is substantiated that the Al 3 Zr particles are highly potent nucleants for Al. In addition, the effects of Al 3 Zr particle size and distribution on Grain Refinement has also been investigated. It has been found that the active Al 3 Zr particles are bigger than previously reported other types of active particles, such as TiB 2 for heterogeneous nucleation in Al alloys. Considering the low growth restriction effect of Zr in Al (the maximum Q -value of Zr in Al is 1.0 K), it is suggested that the significant Grain Refinement of Al resulting from the addition of Zr can be mainly attributed to the heterogeneous nucleation facilitated by the in situ formed Al 3 Zr particles.
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The effect of solute elements on the Grain Refinement of cast Zn
Metallurgical and Materials Transactions A, 2013Co-Authors: Zhilin Liu, Feng Wang, Dong Qiu, John A. Taylor, Ming-xing ZhangAbstract:The effect of both peritectic-forming elements (Cu and Ag) and eutectic-forming elements (Mg and Al) on the Grain Refinement of cast pure Zn was investigated. It is found that these four alloying elements lead to effective Grain Refinement of cast pure Zn, although they have different values of growth restriction factor (Q). Mg and Al seem to have better Grain refining efficiency for cast pure Zn than Cu and Ag. These results raise questions regarding the mechanisms of Grain Refinement in Zn-based alloys, and therefore further studies are required.
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Revisiting the role of peritectics in Grain Refinement of Al alloys
Acta Materialia, 2013Co-Authors: Feng Wang, Mark Alan Easton, Zhilin Liu, Dong Qiu, John A. Taylor, Ming-xing ZhangAbstract:The Grain refining effect of four peritectic-forming solutes (Ti, V, Zr and Nb) as well as three eutectic-forming solutes (Cu, Mg and Si) on pure Al was investigated. Significant Grain Refinement is observed by the addition of peritectic-forming solutes, whereas the addition of eutectic-forming solutes only slightly decreases the Grain size. The mechanisms underlying the Grain Refinement of these alloys were then studied by a new analytical methodology for assessing Grain Refinement that incorporates the effects of both alloy chemistry and nucleant potency. It is found that the low degree of Grain Refinement by the addition of eutectic-forming solutes is mainly attributed to the segregating power of solutes, i.e. the constitutional undercooling contribution. However, peritectic-forming solutes do not only cause Grain Refinement by their segregation power but, more importantly, they introduce copious potent nuclei into the melt and promote significant Grain Refinement via heterogeneous nucleation.
H. Yang - One of the best experts on this subject based on the ideXlab platform.
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Texture analysis of Grain Refinement in undercooled Ni 99.45 B 0.55
Journal of Materials Research, 2001Co-Authors: K. L. Lee, C. H. Shek, H. YangAbstract:Recently, it was demonstrated that Ni 99.45 B 0.55 undergoes Grain Refinement by either remelting or dynamic nucleation at two different undercoolings. In this work, we found that the Grain Refinement by remelting can be characterized by a gradual disappearance of the texture of the initially formed dendrites in the transition regime while the Grain Refinement by dynamic nucleation is characterized by a sudden disappearance of texture.
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Texture analysis of Grain Refinement in undercooled Ni99.45B0.55
Journal of Materials Research, 2001Co-Authors: K. L. Lee, C. H. Shek, H. YangAbstract:Recently, it was demonstrated that Ni99.45B0.55 undergoes Grain Refinement by either remelting or dynamic nucleation at two different undercoolings. In this work, we found that the Grain Refinement by remelting can be characterized by a gradual disappearance of the texture of the initially formed dendrites in the transition regime while the Grain Refinement by dynamic nucleation is characterized by a sudden disappearance of texture.
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Grain Refinement in undercooled metals
MRS Proceedings, 1997Co-Authors: J. Z. Xiao, H. Yang, H.w. KuiAbstract:Recently, it was demonstrated that Grain Refinement in metals can take place through two mechanisms, namely, dynamic nucleation and remelting of initially formed dendrites. In this study, it was found that Ni{sub 99.45}B{sub 0.55} undergoes Grain Refinement, both by dynamic nucleation or by remelting, depending on the initial bulk undercooling just before crystallization. The nature of the Grain Refinement process is confirmed by microstructural analysis of the undercooled specimens.
Peng Cao - One of the best experts on this subject based on the ideXlab platform.
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New approach to analysis of Grain Refinement
2008Co-Authors: D. H. St John, Peng Cao, Mark Alan Easton, Ma QianAbstract:Grain Refinement of aluminium and magnesium alloys has been a challenging topic for decades and this is partly due to the complex nature of the mechanisms occurring during solidification and the lack of a common experimental method allowing comparison of data from different research groups. A new analytical approach that plots Grain size versus the inverse of the growth restriction factor Q enables additional valuable information to be revealed about the efficiency and potency of Grain refiner particles and master alloys. The present paper describes the new analytical approach and then gives examples where insights into the Grain Refinement mechanisms have been achieved. For aluminium alloys, the new analytical approach compares the effectiveness of different master alloys and examines the mechanism of poisoning of Grain Refinement by Zr. For magnesium alloys, the new analytical approach is applied to explain phenomena such as superheating and native Grain Refinement. With this new analytical approach and the knowledge it generates, the potential for the discovery of new or improved refiners is significantly enhanced.
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A new analytical approach to reveal the mechanisms of Grain Refinement
Advanced Engineering Materials, 2007Co-Authors: David H. Stjohn, Peng Cao, Ma Qian, Mark Alan EastonAbstract:This paper presents an overview of a new methodology for investigating the Grain Refinement performance of alloys and master alloys and then uses this methodology to shed new light on the mechanisms occurring during superheating and native Grain Refinement, and the effect of iron and manganese on Grain Refinement in magnesium alloys. The methodology also describes changes in Grain size upon Zr Grain Refinement of Mg and has been used to analyse the potential for the use of SiC to Grain refine Mg-Al alloys. With this new methodology, and the knowledge it generates, the potential for the discovery of new or improved refiners is significantly enhanced.
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Mechanism for Grain Refinement of magnesium alloys by superheating
Scripta Materialia, 2007Co-Authors: Peng Cao, Ma Qian, David H. StjohnAbstract:The mechanisms for Grain Refinement of magnesium alloys by superheating have remained ambiguous since 1931. A model has been proposed on the basis of the recent understanding of the Grain Refinement of both high purity and commercial purity Mg–Al alloys. The model explains most of the experimental observations about superheating. Analysis of the Grain size data obtained from different Mg–Al alloys as a function of the growth restriction factor with and without superheating provides good support to the model.
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Grain Refinement of magnesium alloys
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: David H. Stjohn, Peng Cao, Ma Qian, Mark Alan Easton, Zoe HildebrandAbstract:The literature on Grain Refinement of magnesium alloys is reviewed with regard to two broad groups of alloys: alloys that contain aluminum and alloys that do not contain aluminum. The alloys that are free of aluminum are generally very well refined by Zr master alloys. On the other hand, the understanding of Grain Refinement in aluminum bearing alloys is poor and in many cases confusing probably due to the interaction between impurity elements and aluminum in affecting the potency of nucleant particles. A Grain Refinement model that was developed for aluminum alloys is presented, which takes into account both alloy chemistry and nucleant particle potency. This model is applied to experimental data for a range of magnesium alloys. It is shown that by using this analytical approach, new information on the Refinement of magnesium alloys is obtained as well as providing a method of characterizing the effectiveness of new refiners. The new information revealed by the model has identified new directions for further research. Future research needs to focus on gaining a better understanding of the detailed mechanisms by which Refinement occurs and gathering data to improve our ability to predict Grain Refinement for particular combinations of alloy and impurity chemistry and nucleant particles.
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Effect of Common Impurity Elements on Grain Refinement of Magnesium Alloys
2005Co-Authors: Peng CaoAbstract:There has been much confusion evident in the literature in terms of the influence of impurity elements on Grain Refinement of magnesium alloys. This thesis addresses how impurity elements such as iron, manganese, carbon and beryllium affect Grain Refinement in magnesium alloys. The thesis starts with an investigation into the effect of the uptake of iron on Grain Refinement of Mg-Zr alloys. The highly detrimental influence of the uptake of iron on Grain Refinement in Mg-Zr alloys has been confirmed. The gradual loss of Grain Refinement of Mg-Zr alloys partly arises from the consumption of Zr by the formation of Fe2Zr via the reaction between soluble Zr and Fe picked up from mild steel crucibles. (Settling of undissolved Zr particles also partly attributes to the gradual loss of Grain Refinement.) The morphological evolution of Zr-rich cores from circular to rosette-like has been reported here for the first time. In contrast to the detrimental effect in Mg-Zr alloys, a positive effect of iron has been observed in Grain Refinement of Mg-Al based alloys. The addition of iron in the form of anhydrous FeCl3 produces significant Grain Refinement of high-purity Mg-Al alloys. Obvious Grain Refinement was also achieved through the uptake of iron from steel crucible surfaces; however, the addition of Fe powder in the form of an ALTABTM Fe75 powder compact (75%Fe, 15%Al and 10% Na-free flux) did not give rise to Grain Refinement. The results obtained from both the Grain Refinement tests conducted in aluminium titanite crucibles and an ultra-low carbon 316L stainless crucible indicate that the Grain Refinement of Mg-Al alloys by iron inoculation has little to do with the Al4C3 hypothesis. The nucleant particles have been clarified to be Fe- and Al-rich intermetallics. The effect of manganese on the Grain Refinement of high purity Mg-Al based alloys and commercially available AZ31 alloys has been investigated using an Al-60%Mn master alloy splatter at 730 aC in aluminium titanite crucibles. Grain Refinement was readily achievable in these alloys. Electron microprobe analyses revealed that prior to the addition of extra manganese the majority of the intermetallic particles found in AZ31 are of the Al8Mn5 type. However, after the addition of extra manganese in the range of 0.1% to 1.0%, the predominant group of intermetallic particles changed to the metastable AlMn type. This leads to a hypothesis that the metastable AlMn intermetallic particles are more effective than Al8Mn5 as nucleation sites for magnesium Grains. The hypothesis was supported by the observation that a long period of holding at 730 aC led to an increase in Grain size, due probably to the transformation of the metastable AlMn to the stable Al8Mn5. Native Grain Refinement in magnesium alloys has been clarified. Based on the fact that native Grain Refinement is an exclusive feature of high purity Mg-Al alloys, it is hypothesized that Al4C3 particles act as nucleation centres. This is also the mechanism of carbon Grain Refinement of Mg-Al alloys. A trace of beryllium leads to dramatic Grain coarsening in Mg-Al alloys at normal cooling rates. Apart from Mg-Al alloys, a trace of beryllium also causes considerable Grain coarsening in Mg-Zn, Mg-Ca, Mg-Ce, Mg-Nd and also hinders Grain Refinement of magnesium alloys by Zr. Modelling Grain Refinement to predict the final Grain size has been made on the basis of understanding of existing models. The modified model has resolved a fundamental gap in the relative Grain size model using a more universal expression of solute concentration in the liquid.
Dong Qiu - One of the best experts on this subject based on the ideXlab platform.
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current research progress in Grain Refinement of cast magnesium alloys a review article
Journal of Alloys and Compounds, 2015Co-Authors: Yahia Ali, Dong Qiu, Bin Jiang, Fusheng Pan, Ming-xing ZhangAbstract: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.
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the Grain Refinement mechanism of cast aluminium by zirconium
Acta Materialia, 2013Co-Authors: Feng Wang, Mark Alan Easton, Zhilin Liu, Dong Qiu, J A Taylor, Ming-xing ZhangAbstract:Abstract The mechanism underlying the Grain Refinement of cast aluminium by zirconium has been studied through examination of a range of Al alloys with increasing Zr contents. Pro-peritectic Al 3 Zr particles are reproducibly identified at or near the Grain centres in Grain-refined alloy samples based on the observations of optical microscopy, scanning electron microscopy and X-ray diffraction. From the crystallographic study using the edge-to-edge matching model, electron backscatter diffraction and transmission electron microscopy, it is substantiated that the Al 3 Zr particles are highly potent nucleants for Al. In addition, the effects of Al 3 Zr particle size and distribution on Grain Refinement has also been investigated. It has been found that the active Al 3 Zr particles are bigger than previously reported other types of active particles, such as TiB 2 for heterogeneous nucleation in Al alloys. Considering the low growth restriction effect of Zr in Al (the maximum Q -value of Zr in Al is 1.0 K), it is suggested that the significant Grain Refinement of Al resulting from the addition of Zr can be mainly attributed to the heterogeneous nucleation facilitated by the in situ formed Al 3 Zr particles.
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The effect of solute elements on the Grain Refinement of cast Zn
Metallurgical and Materials Transactions A, 2013Co-Authors: Zhilin Liu, Feng Wang, Dong Qiu, John A. Taylor, Ming-xing ZhangAbstract:The effect of both peritectic-forming elements (Cu and Ag) and eutectic-forming elements (Mg and Al) on the Grain Refinement of cast pure Zn was investigated. It is found that these four alloying elements lead to effective Grain Refinement of cast pure Zn, although they have different values of growth restriction factor (Q). Mg and Al seem to have better Grain refining efficiency for cast pure Zn than Cu and Ag. These results raise questions regarding the mechanisms of Grain Refinement in Zn-based alloys, and therefore further studies are required.
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Revisiting the role of peritectics in Grain Refinement of Al alloys
Acta Materialia, 2013Co-Authors: Feng Wang, Mark Alan Easton, Zhilin Liu, Dong Qiu, John A. Taylor, Ming-xing ZhangAbstract:The Grain refining effect of four peritectic-forming solutes (Ti, V, Zr and Nb) as well as three eutectic-forming solutes (Cu, Mg and Si) on pure Al was investigated. Significant Grain Refinement is observed by the addition of peritectic-forming solutes, whereas the addition of eutectic-forming solutes only slightly decreases the Grain size. The mechanisms underlying the Grain Refinement of these alloys were then studied by a new analytical methodology for assessing Grain Refinement that incorporates the effects of both alloy chemistry and nucleant potency. It is found that the low degree of Grain Refinement by the addition of eutectic-forming solutes is mainly attributed to the segregating power of solutes, i.e. the constitutional undercooling contribution. However, peritectic-forming solutes do not only cause Grain Refinement by their segregation power but, more importantly, they introduce copious potent nuclei into the melt and promote significant Grain Refinement via heterogeneous nucleation.
