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Amauri Garcia - One of the best experts on this subject based on the ideXlab platform.
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Electrochemical behavior of Zn-rich Zn–Cu peritectic alloys affected by macroSegregation and microstructural array
Electrochimica Acta, 2012Co-Authors: Wislei R. Osório, Leandro C. Peixoto, Crystopher Brito, Amauri GarciaAbstract:Abstract The aim of this experimental investigation is to evaluate the electrochemical behavior of an as-cast Zn-rich Zn–Cu peritectic alloy as a function of both the solute macroSegregation profile and the microstructure cellular spacing. A directional solidification apparatus was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization techniques and an equivalent circuit analysis were used to evaluate the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that both copper content and cell spacing are significantly affected by the position along the casting length from the cooled bottom of the casting. These parameters play interdependent roles on the resulting corrosion behavior. Samples which are closer to the casting cooled surface are more affected by the solute Inverse Segregation, i.e. have a Cu content that is higher than the alloy nominal composition. This is shown to be a driving-force leading to a decrease in the corrosion resistance. However, for other samples with similar Cu content and close to the nominal alloy composition, the cell spacing seems to be the driving-force associated with the corrosion resistance and for these cases finer microstructures are shown to be related to higher corrosion resistance.
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MacroSegregation and microstructure dendritic array affecting the electrochemical behaviour of ternary Al-Cu-Si alloys
Electrochimica Acta, 2011Co-Authors: Wislei R. Osório, Ivaldo L. Ferreira, Daniel J. Moutinho, Leandro C. Peixoto, Amauri GarciaAbstract:Abstract The aim of the present study is to evaluate the electrochemical corrosion behaviour of ternary as-cast Al–Cu–Si alloys. Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that silicon and copper contents, which are affected by position in casting due to macroSegregation, and the dendrite arm spacing, can play an interdependent role on the corrosion behaviour. For the region with predominant Cu Inverse Segregation, i.e., close to the casting surface, the Cu content is the driving-force leading to a decrease in the corrosion resistance, but the favorable effect of the fineness of the dendritic array has also to be taken into account. However, from secondary dendrite arm spacings of about 15 μm up to coarser dendritic arrays, the Si particles seem to be the driving-forces related to the corrosion resistance and for these cases coarser microstructures were shown to improve the corrosion resistance.
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dendritic arm spacing affecting mechanical properties and wear behavior of al sn and al si alloys directionally solidified under unsteady state conditions
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2010Co-Authors: Kleber S. Cruz, Elisangela Dos Santos Meza, Frederico Augusto Pires Fernandes, Jose Maria Do Vale Quaresma, Luiz Carlos Casteletti, Amauri GarciaAbstract:Alloys of Al-Sn and Al-Si are widely used in tribological applications such as cylinder liners and journal bearings. Studies of the influence of the as-cast microstructures of these alloys on the final mechanical properties and wear resistance can be very useful for planning solidification conditions in order to permit a desired level of final properties to be achieved. The aim of the present study was to contribute to a better understanding about the relationship between the scale of the dendritic network and the corresponding mechanical properties and wear behavior. The Al-Sn (15 and 20 wt pct Sn) and Al-Si (3 and 5 wt pct Si) alloys were directionally solidified under unsteady-state heat flow conditions in water-cooled molds in order to permit samples with a wide range of dendritic spacings to be obtained. These samples were subjected to tensile and wear tests, and experimental quantitative expressions correlating the ultimate tensile strength (UTS), yield tensile strength, elongation, and wear volume to the primary dendritic arm spacing (DAS) have been determined. The wear resistance was shown to be significantly affected by the scale of primary dendrite arm spacing. For Al-Si alloys, the refinement of the dendritic array improved the wear resistance, while for the Al-Sn alloys, an opposite effect was observed, i.e., the increase in primary dendrite arm spacing improved the wear resistance. The effect of Inverse Segregation, which is observed for Al-Sn alloys, on the wear resistance is also discussed.
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alloy composition and metal mold heat transfer efficiency affecting Inverse Segregation and porosity of as cast al cu alloys
Materials & Design, 2009Co-Authors: Alexandre P. Boeira, Ivaldo L. Ferreira, Amauri GarciaAbstract:Abstract Porosity is one of the most important defects in metals casting. In this study, macroSegregation and porosity formation were investigated by a numerical model and by solidification experiments. The local composition along the length of Al–Cu castings was calculated by the macroSegregation model and used as an input parameter for simulation of microporosity. The effects exerted by gravity upon the solute redistribution and microporosity are also encompassed by this model. X-ray fluorescence spectrometry was used to determine the Segregation profiles. The measurement of microporosity was performed using pyknometry analysis. The results have demonstrated that both the decrease on alloy solute content and the increase on metal/mold heat transfer coefficient are connected to lower porosity levels at regions closer to the casting surface.
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Inverse Segregation during transient directional solidification of an Al–Sn alloy: Numerical and experimental analysis
Materials Chemistry and Physics, 2009Co-Authors: Kleber S. Cruz, Ivaldo L. Ferreira, José E. Spinelli, Noé Cheung, Amauri GarciaAbstract:Abstract In this article macroSegregation phenomenon is investigated by a finite volume numerical modeling technique and by upward unidirectional solidification of an Al–23 wt%Sn alloy casting. The numerical model consists of an explicit/implicit time integration scheme to couple thermal and solutal fields. The experimental solidification set-up allows a vertically aligned macrostructure to be obtained. The concentration profile was obtained by an X-ray fluorescence spectrometry technique carried out in cylindrical slices representing certain position inside the casting from the casting/chill interface. The simulated and experimental temperature and concentration profiles are compared and very good agreement has been observed.
Ivaldo L. Ferreira - One of the best experts on this subject based on the ideXlab platform.
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MacroSegregation and microstructure dendritic array affecting the electrochemical behaviour of ternary Al-Cu-Si alloys
Electrochimica Acta, 2011Co-Authors: Wislei R. Osório, Ivaldo L. Ferreira, Daniel J. Moutinho, Leandro C. Peixoto, Amauri GarciaAbstract:Abstract The aim of the present study is to evaluate the electrochemical corrosion behaviour of ternary as-cast Al–Cu–Si alloys. Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that silicon and copper contents, which are affected by position in casting due to macroSegregation, and the dendrite arm spacing, can play an interdependent role on the corrosion behaviour. For the region with predominant Cu Inverse Segregation, i.e., close to the casting surface, the Cu content is the driving-force leading to a decrease in the corrosion resistance, but the favorable effect of the fineness of the dendritic array has also to be taken into account. However, from secondary dendrite arm spacings of about 15 μm up to coarser dendritic arrays, the Si particles seem to be the driving-forces related to the corrosion resistance and for these cases coarser microstructures were shown to improve the corrosion resistance.
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alloy composition and metal mold heat transfer efficiency affecting Inverse Segregation and porosity of as cast al cu alloys
Materials & Design, 2009Co-Authors: Alexandre P. Boeira, Ivaldo L. Ferreira, Amauri GarciaAbstract:Abstract Porosity is one of the most important defects in metals casting. In this study, macroSegregation and porosity formation were investigated by a numerical model and by solidification experiments. The local composition along the length of Al–Cu castings was calculated by the macroSegregation model and used as an input parameter for simulation of microporosity. The effects exerted by gravity upon the solute redistribution and microporosity are also encompassed by this model. X-ray fluorescence spectrometry was used to determine the Segregation profiles. The measurement of microporosity was performed using pyknometry analysis. The results have demonstrated that both the decrease on alloy solute content and the increase on metal/mold heat transfer coefficient are connected to lower porosity levels at regions closer to the casting surface.
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Inverse Segregation during transient directional solidification of an Al–Sn alloy: Numerical and experimental analysis
Materials Chemistry and Physics, 2009Co-Authors: Kleber S. Cruz, Ivaldo L. Ferreira, José E. Spinelli, Noé Cheung, Amauri GarciaAbstract:Abstract In this article macroSegregation phenomenon is investigated by a finite volume numerical modeling technique and by upward unidirectional solidification of an Al–23 wt%Sn alloy casting. The numerical model consists of an explicit/implicit time integration scheme to couple thermal and solutal fields. The experimental solidification set-up allows a vertically aligned macrostructure to be obtained. The concentration profile was obtained by an X-ray fluorescence spectrometry technique carried out in cylindrical slices representing certain position inside the casting from the casting/chill interface. The simulated and experimental temperature and concentration profiles are compared and very good agreement has been observed.
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Alloy composition and metal/mold heat transfer efficiency affecting Inverse Segregation and porosity of as-cast Al–Cu alloys
Materials & Design, 2009Co-Authors: Alexandre P. Boeira, Ivaldo L. Ferreira, Amauri GarciaAbstract:Abstract Porosity is one of the most important defects in metals casting. In this study, macroSegregation and porosity formation were investigated by a numerical model and by solidification experiments. The local composition along the length of Al–Cu castings was calculated by the macroSegregation model and used as an input parameter for simulation of microporosity. The effects exerted by gravity upon the solute redistribution and microporosity are also encompassed by this model. X-ray fluorescence spectrometry was used to determine the Segregation profiles. The measurement of microporosity was performed using pyknometry analysis. The results have demonstrated that both the decrease on alloy solute content and the increase on metal/mold heat transfer coefficient are connected to lower porosity levels at regions closer to the casting surface.
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Gravity-driven Inverse Segregation during transient upward directional solidification of Sn–Pb hypoeutectic alloys
Journal of Alloys and Compounds, 2008Co-Authors: Ivaldo L. Ferreira, José E. Spinelli, Amauri GarciaAbstract:Abstract Upward unidirectional solidification experiments were performed with Sn–4.0 wt.%Pb and Sn–12.5 wt.%Pb alloys. Transitory conditions of heat flow extraction were sustained during these solidification experiments, which mean that all solidification variables (cooling rate, tip growth rate, thermal gradient, and metal/mold heat transfer coefficient) have varied freely along solidification. In this work, the macroSegregation phenomenon is experimentally and theoretically evaluated considering both solidification shrinkage and gravity induced flows. The numerical model is based on a one-dimensional solution consisting of an implicit/explicit time integration scheme to couple thermal and solutal fields, which is supported by a finite volume numerical modeling technique to be solved. The applied solidification system permitted columnar growth to prevail along the castings. Since the Pb-rich melt tends to flow downward (in favor of the gravity vector), the bottom of the castings exhibited positive Pb content, mainly induced by gravity. The numerically simulated and experimental temperature and concentration profiles were compared and a very good agreement has been observed.
W. S. Hwang - One of the best experts on this subject based on the ideXlab platform.
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Comparison of phosphor bronze metal sheet produced by twin roll casting and horizontal continuous casting
Journal of Materials Engineering and Performance, 1998Co-Authors: J. D. Hwang, W. S. HwangAbstract:Much effort recently has been expended to study the strip casting process used to produce thin metal strip with a near final thickness. This process eliminates the need for hot rolling, consumes less energy, and offers a feasible method of producing various hard-to-shape alloys. The finer microstructure that results from the high cooling rate used during the casting process enhances mechanical properties. In this study, strips of phosphor bronzes (Cu-Sn-P) metal were produced using a twin roll strip casting process as well as a conventional horizontal continuous casting (HCC) process. The microstructures, macroSegregations, textures, and mechanical properties of the as-cast and as-rolled metal sheet produced by these two methods were examined carefully for comparative purposes. The results indicate that cast strip produced by a twin roll caster exhibit significantly less Inverse Segregation of tin compared to that produced by the HCC process. The mechanical properties including tensile strength, elongation, and microhardness of the products produced by the twin roll strip casting process are comparable to those of the HCC processed sheet. These properties meet specifications JIS H3110 and ASTM B 103M for commercial phosphor bronze sheet. The texture of the as-rolled sheet from these two processes, as measured from XRD pole figures, were found to be virtually the same, even though a significant difference exists between them in the as-cast condition.
J. R. Cahoon - One of the best experts on this subject based on the ideXlab platform.
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Solidification of hypereutectic Al-38 Wt Pct Cu alloy in microgravity and in unit gravity
Metallurgical and Materials Transactions A, 1997Co-Authors: K. N. Tandon, J. R. CahoonAbstract:Solidification in microgravity aboard the space shuttle Endeavour resulted in a dramatic change in the morphology of the primary Al_2Cu phase compared to ground-based solidification in unit gravity. An Al-38 wt pct Cu ingot directionally solidified at a rate of 0.015 mm/s with a temperature gradient of 1.69 K/mm exhibited large, well-formed dendrites of primary Al_2Cu phase. Ingots solidified under similar conditions in unit gravity contained primary Al_2Cu phase with smooth, faceted surfaces. The primary Al_2Cu phase spacing in the microgravity ingot was much greater than that in the unit gravity ingot, 670 µm compared to 171 µm. It is suggested that thermosolutal mixing in the unit gravity ingot reduces the buildup of an Al-rich layer at the solid/liquid interface, which increases the stability of the interface resulting in smooth, faceted particles of Al_2Cu phase. It is also suggested that the large difference in primary phase spacings is due mostly to the difference in morphology rather than changes in parameters that might influence dendrite ripening mechanisms. The presence or absence of gravity had no effect on the interlamellar spacing of the inter-Al_2Cu phase eutectic. The ingot solidified in microgravity exhibited almost no longitudinal macroSegregation, in agreement with the theory of Inverse Segregation in the absence of thermosolutal convection. The ingot solidified in unit gravity exhibited considerable longitudinal macroSegregation, with the chilled end having about 6 wt pct more Cu than the average composition. It is not clear whether the Segregation results from thermosolutal convection during solidification or from sedimentation during melting.
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A re-evaluation of Inverse Segregation in the Al(rich)-Cu system
Materials Science and Engineering: A, 1994Co-Authors: J. R. CahoonAbstract:Abstract The chill-face Inverse Segregation in Al(rich)-Cu alloy is re-calculated using an updated phase diagram and specific volume data. The newly calculated values of chill-face Segregation are considerably higher than experimental results and previously calculated values. It was previously assumed that there was no concentration gradient in the liquid alloy at the dendrite-liquid interface and the good agreement between the experimental and calculated values of chill-face Inverse Segregation was cited to confirm this assumption. Agreement between the experimental values and calculated values using the updated specific volume data can be obtained if it is assumed that a concentration gradient exists in the liquid at the solid-liquid interface, and an effective distribution coefficient rather than the equilibrium value is used in the calculations. The values of effective distribution coefficient required in the calculations are presented.
J. D. Hwang - One of the best experts on this subject based on the ideXlab platform.
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Comparison of phosphor bronze metal sheet produced by twin roll casting and horizontal continuous casting
Journal of Materials Engineering and Performance, 1998Co-Authors: J. D. Hwang, W. S. HwangAbstract:Much effort recently has been expended to study the strip casting process used to produce thin metal strip with a near final thickness. This process eliminates the need for hot rolling, consumes less energy, and offers a feasible method of producing various hard-to-shape alloys. The finer microstructure that results from the high cooling rate used during the casting process enhances mechanical properties. In this study, strips of phosphor bronzes (Cu-Sn-P) metal were produced using a twin roll strip casting process as well as a conventional horizontal continuous casting (HCC) process. The microstructures, macroSegregations, textures, and mechanical properties of the as-cast and as-rolled metal sheet produced by these two methods were examined carefully for comparative purposes. The results indicate that cast strip produced by a twin roll caster exhibit significantly less Inverse Segregation of tin compared to that produced by the HCC process. The mechanical properties including tensile strength, elongation, and microhardness of the products produced by the twin roll strip casting process are comparable to those of the HCC processed sheet. These properties meet specifications JIS H3110 and ASTM B 103M for commercial phosphor bronze sheet. The texture of the as-rolled sheet from these two processes, as measured from XRD pole figures, were found to be virtually the same, even though a significant difference exists between them in the as-cast condition.
