The aim of this work was to evaluate the electrochemical behaviour of hypoeutectic Al-Cu alloys immersed in two different solutions containing sulphate and chloride ions, respectively. The influence of Al2Cu associate...The aim of this work was to evaluate the electrochemical behaviour of hypoeutectic Al-Cu alloys immersed in two different solutions containing sulphate and chloride ions, respectively. The influence of Al2Cu associated to the dendritic arm spacing on the general corrosion resistance of such alloys is analysed. The typical microstructural pattern was examined by using scanning electron microscope. The corrosion tests were performed in both 0.5 M sulphuric acid and 0.5 M NaCl solutions at 25℃ by using an electrochemical impedance spectroscopy (EIS) technique and potentiodynamic polarization curves. Equivalent circuits by using the ZView software, were also used to provide quantitative support for the discussions. It was found that as the Cu content increased (i.e., increasing the Al2Cu fraction), a higher susceptibility to the corrosion action in the NaCl solution is detected. In contrast, the tests carried out in the H2SO4 solution resulted in similar corrosion,rates for the three different hypoeutectic alloys.展开更多
AI-Pb alloys with monotectic and hypermonotectic compositions were directionally solidified under unsteady- state heat flow conditions. The cooling curves recorded during solidification allowed solidification thermal ...AI-Pb alloys with monotectic and hypermonotectic compositions were directionally solidified under unsteady- state heat flow conditions. The cooling curves recorded during solidification allowed solidification thermal parameters such as the cooling rate (T), growth rate (v) and thermal gradient (G) to be experimentally determined. Different microstructural patterns have been associated with the alloy solute content, i.e., AI-1.2 and 2.1 wt% Pb. A sequence of morphologies from the bottom to the top of the A1-1.2 wt% Pb alloy casting (monotectic) can be observed: Pb-rich droplets in the aluminum-rich matrix, followed by a region of microstructural transition formed by droplets and fibers and finally by a mixture of fibers and strings of pearls. A completely fibrous structure (without transition) has been observed along the entire AI-2.1 wt% Pb alloy casting (hypermonotectic). The interphase spacing (λ) was measured along the casting length, and experimental correlations between λand experimental solidification thermal parameters have been established. Power laws with a -2.2 exponent expressing λ as a function of the growth rate, v, were found to better represent the fibrous growth of both AI-Pb alloys. Moreover, a single experimental law expressing λ as a function of both G and v was found to describe the fibrous growth of both the monotectic and the hypermonotectic alloys experimentally examined.展开更多
In the present experimental investigation,Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(G...In the present experimental investigation,Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(GR),cooling rate(CR),secondary dendrite arm spacing(λ2),Vickers microhardness(HV),and corrosion behavior in a 0.5 M NaCl solution.The intermetallic phases of the as-solidified microstructures,that is,h-Al2Cu,S–Al2CuMg,and x-Al7Cu2 Fe,are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software,optical microscopy,and scanning electron microscopy/energy-dispersive spectroscopy.Moreover,electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings.Hall–Petch-type equations are proposed to represent the HV dependence onλ2.It is shown that the addition of Mg to the Al–Cu alloy has led to a considerable increase in HV;however,the Al–Cu binary alloy is shown to have lower corrosion current density(icorr)as well as higher polarization resistance as compared to the corresponding results of the Al–Cu–Mg ternary alloy.展开更多
The present investigation is based on the results of a directionally solidified (DS) Sn-9 wt%Zn-2 wt%Cu alloy, including primary/secondary/tertiary dendrite arm spacings of the Sn-rich matrix, the morphologies of th...The present investigation is based on the results of a directionally solidified (DS) Sn-9 wt%Zn-2 wt%Cu alloy, including primary/secondary/tertiary dendrite arm spacings of the Sn-rich matrix, the morphologies of the eutectic mixture and the corresponding interphase spacing, the nature and proportion of the Cu-Zn intermetallic compound (IMC). The main purpose is to establish interrelations of these microstructure features with experimental solidification thermal parameters, such as cooling rates and growth rates (v), macrosegregation and hardness. Such interrelations are interesting for both industry and academy since they represent a tool permitting the preprogramming of final properties based on the design of the microstructure. In the case of Sn-Zn-Cu alloys, hardly anything is known about the combined effects of the length scale of the microstructure and fraction and distribution of the primary IMC on hardness. The alloy microstructure is composed of a β-Sn dendritic region, surrounded by a eutectic mixture of α-Zn and β-Sn phases and the γ-Cu5Zn8 IMC. The eutectic interphase spacing varies in the range 1.2-3.6 μm, with the α-Zn phase having a globular morphology for ν 〉 0.5 mm/s and a needle-like morphology for ν 〈 0.3 mm/s. A modified Hall-Petch-type experimental expression relating hardness to the interphase spacing is proposed.展开更多
基金CNPq-National Council for Scientific and Technological Development(Grant:407871/2018-7)CAPES-Coordenação de Aperfeiçoamento de Pessoal de Nível Superior,Brazil,for the financial support。
文摘The aim of this work was to evaluate the electrochemical behaviour of hypoeutectic Al-Cu alloys immersed in two different solutions containing sulphate and chloride ions, respectively. The influence of Al2Cu associated to the dendritic arm spacing on the general corrosion resistance of such alloys is analysed. The typical microstructural pattern was examined by using scanning electron microscope. The corrosion tests were performed in both 0.5 M sulphuric acid and 0.5 M NaCl solutions at 25℃ by using an electrochemical impedance spectroscopy (EIS) technique and potentiodynamic polarization curves. Equivalent circuits by using the ZView software, were also used to provide quantitative support for the discussions. It was found that as the Cu content increased (i.e., increasing the Al2Cu fraction), a higher susceptibility to the corrosion action in the NaCl solution is detected. In contrast, the tests carried out in the H2SO4 solution resulted in similar corrosion,rates for the three different hypoeutectic alloys.
基金The authors are grateful to FAPESP-São Paulo Research Foundation,Brazil(2014/50502-5 and 2017/16058-9)Capes-Coordenação de Aperfeiçoamento de Pessoal de Nível Superior,Brazil(Funding code 001)and CNPq-National Council for Scientific and Technological Development(406239/2018-5)for their financial supportThe authors would like to thank the Brazilian Nanotechnology National Laboratory–LNNano for allowing us to use its facilities.
基金the financial support provided by FAPESP(The Scientific Research Foundation of the State of Sao Paulo,Brazil)and CNPq(The Brazilian Research Council)
文摘AI-Pb alloys with monotectic and hypermonotectic compositions were directionally solidified under unsteady- state heat flow conditions. The cooling curves recorded during solidification allowed solidification thermal parameters such as the cooling rate (T), growth rate (v) and thermal gradient (G) to be experimentally determined. Different microstructural patterns have been associated with the alloy solute content, i.e., AI-1.2 and 2.1 wt% Pb. A sequence of morphologies from the bottom to the top of the A1-1.2 wt% Pb alloy casting (monotectic) can be observed: Pb-rich droplets in the aluminum-rich matrix, followed by a region of microstructural transition formed by droplets and fibers and finally by a mixture of fibers and strings of pearls. A completely fibrous structure (without transition) has been observed along the entire AI-2.1 wt% Pb alloy casting (hypermonotectic). The interphase spacing (λ) was measured along the casting length, and experimental correlations between λand experimental solidification thermal parameters have been established. Power laws with a -2.2 exponent expressing λ as a function of the growth rate, v, were found to better represent the fibrous growth of both AI-Pb alloys. Moreover, a single experimental law expressing λ as a function of both G and v was found to describe the fibrous growth of both the monotectic and the hypermonotectic alloys experimentally examined.
基金financial support provided by IFPA-Federal Institute of Education,Science and Technology of Pará,UFPA-Federal University of Pará,and CNPq-The Brazilian Research Council(Grants 302846/2017-4,400634/2016-3,and 301600/2015-5)CAPES-Coordination of Superior Level Staff Improvement,Brazil,and FAPESP(Sao Paulo Research Foundation,Brazil:Grant 2017/16058-9)
文摘In the present experimental investigation,Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(GR),cooling rate(CR),secondary dendrite arm spacing(λ2),Vickers microhardness(HV),and corrosion behavior in a 0.5 M NaCl solution.The intermetallic phases of the as-solidified microstructures,that is,h-Al2Cu,S–Al2CuMg,and x-Al7Cu2 Fe,are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software,optical microscopy,and scanning electron microscopy/energy-dispersive spectroscopy.Moreover,electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings.Hall–Petch-type equations are proposed to represent the HV dependence onλ2.It is shown that the addition of Mg to the Al–Cu alloy has led to a considerable increase in HV;however,the Al–Cu binary alloy is shown to have lower corrosion current density(icorr)as well as higher polarization resistance as compared to the corresponding results of the Al–Cu–Mg ternary alloy.
基金financial support provided by FAPESP(So Paulo Research Foundation,Brazil:Grants 2013/08259-3 and 2015/11863-5)CNPq
文摘The present investigation is based on the results of a directionally solidified (DS) Sn-9 wt%Zn-2 wt%Cu alloy, including primary/secondary/tertiary dendrite arm spacings of the Sn-rich matrix, the morphologies of the eutectic mixture and the corresponding interphase spacing, the nature and proportion of the Cu-Zn intermetallic compound (IMC). The main purpose is to establish interrelations of these microstructure features with experimental solidification thermal parameters, such as cooling rates and growth rates (v), macrosegregation and hardness. Such interrelations are interesting for both industry and academy since they represent a tool permitting the preprogramming of final properties based on the design of the microstructure. In the case of Sn-Zn-Cu alloys, hardly anything is known about the combined effects of the length scale of the microstructure and fraction and distribution of the primary IMC on hardness. The alloy microstructure is composed of a β-Sn dendritic region, surrounded by a eutectic mixture of α-Zn and β-Sn phases and the γ-Cu5Zn8 IMC. The eutectic interphase spacing varies in the range 1.2-3.6 μm, with the α-Zn phase having a globular morphology for ν 〉 0.5 mm/s and a needle-like morphology for ν 〈 0.3 mm/s. A modified Hall-Petch-type experimental expression relating hardness to the interphase spacing is proposed.