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Alüminyum gümüş alaşımlarının oyuklanma davranışı

Pitting behavior of Al-Ag alloys

  1. Tez No: 39499
  2. Yazar: GÜRHAN TOPGÜL
  3. Danışmanlar: DOÇ.DR. MUSTAFA ÜRGEN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Metalurji Mühendisliği, Metallurgical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1994
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 71

Özet

In galvanostatic experiments, programmable electrometer, Keithley 617, was added to potentiostatic experiment system. During the experiments 1 mA/cm2 current density was applied until a fixed potential obtained. When potential reached a fixed value current was interrupted in 3 seconds and then potential change was observed. During the experiments potential versus time data measured by the programmable electrometer. In these experiments, it has been found that silver additions to aluminum decreased anodic over voltage like copper, and did not change open circuit corrosion potential after certain values unlike copper (this value was approximately 0.9 % Ag). Therefore, it can be said that silver effected pitting behavior of aluminum by changing its open circuit corrosion potential in pit solution. In addition to performed experiments in saturated AICI3, to understand the effect of silver on corrosion behavior of aluminum in AICI3 solution better, anodic and cathodic polarization curves were obtained for pure aluminum, pure silver and some aluminum-silver alloys (0.02, 0.9, 5 % Ag) According to the results obtained from anodic and cathodic polarization curves, it has been understood that silver changed, unlike copper, corrosion potential of aluminum by accelerating especially the anodic reaction. Intermetallic particles that can form in aluminum alloys are very important in governing the pitting and localized corrosion properties of Al alloys. The determination of electrochemical properties of the phases is very important in terms of better understanding of corrosion behavior of the alloy which contain these intermetallics. Ag2AI intermetallic is the main precipitated phase in Aluminum-Silver system and preferentially precipitates in grain boundaries. To determine corrosion behavior of Ag2AI intermetalic with respect to Al matrix, the corrosion and pitting potential of Ag2AI intermetalic was investigated in 3.5 % NaCI solutions of different pH's. The results obtained from this study can be summarized as follow. 1. It has been observed that silver additions to aluminum up to 15 % Ag did not change significantly the pitting potential of aluminum. 2. Experimentally obtained pitting potentials of Al-Ag alloys is in accordance with the pitting potential values calculated theoretically from the model of Galvele, within ± 40 mV. IX

Özet (Çeviri)

Pitting Behavior of A l-Ağ Alloys SUMMARY Aluminium and its alloys are a group of very important materials for engineering applications because of their lightness, malleability, resistance to corrosion, mechanical and physical properties. Since aluminum is a light and soft metal the additions of various alloying elements are necessary to improve its strength. VVhile strength is increased with alloying elements its corrosion resistance is decreased. This creates some problems during the use of aluminum alloys. To optimize strength and corrosion resistance of aluminum, another alloying elements are added to aluminum. Cu, Mn, Si, Mg, Zn, and Sn are used as primary alloying elements, besides these elements Li, Cr, Ni, Ağ, Zr, V, Ga, Ti, Pb, Co, Cd, Be, Bi are also added to aluminum alloys. The main aim of both majör and minör alloying is to improve mechanical and physical properties. Although silver has a significantly high solubility in aluminum and provides age hardenability in the alloy, it is not used as primary alloying element because of economic reasons. Hovvever recently, addition of low amounts of silver (< 1% Ağ), to the high strength Al alloys such as AI-Cu- Mg, AI-Zn-Mg and AI-Cu-Li are becoming increasingly popular. Silver changes significantly precipitation process in these alloys and improves strength. The use of silver as an alloying element in Weldalite-049 that was developed by NASA for space programs provided better understanding of the importance of silver in Al alloys. The studies on the effect of silver on the general and localized corrosion of aluminum were conducted with alloys having high silver content (10-20 %Ag). in the literatüre, there are no systematic studies on the corrosion of binary aluminum - silver alloys with low silver (up to 1 %Ag). Hovvever, it has been proposed that silver additions to AI-Cu-Mg and AI-Zn-Mg systems provided resistance to stress corrosion cracking and intergranular corrosion. in this investigation, the effect of silver on localized corrosion of aluminum was studied systematically in 3.5 % NaCI. in accordance with this objective, binary AI-Ag alloys with various contents of Ağ and AggAl intermetallic were prepared. Aluminum-Silver alloys and Ag2AI intermetallic were prepared from high purity materials (99.999 %AI, 99.99 % viIn galvanostatic experiments, programmable electrometer, Keithley 617, was added to potentiostatic experiment system. During the experiments 1 mA/cm2 current density was applied until a fixed potential obtained. When potential reached a fixed value current was interrupted in 3 seconds and then potential change was observed. During the experiments potential versus time data measured by the programmable electrometer. In these experiments, it has been found that silver additions to aluminum decreased anodic over voltage like copper, and did not change open circuit corrosion potential after certain values unlike copper (this value was approximately 0.9 % Ag). Therefore, it can be said that silver effected pitting behavior of aluminum by changing its open circuit corrosion potential in pit solution. In addition to performed experiments in saturated AICI3, to understand the effect of silver on corrosion behavior of aluminum in AICI3 solution better, anodic and cathodic polarization curves were obtained for pure aluminum, pure silver and some aluminum-silver alloys (0.02, 0.9, 5 % Ag) According to the results obtained from anodic and cathodic polarization curves, it has been understood that silver changed, unlike copper, corrosion potential of aluminum by accelerating especially the anodic reaction. Intermetallic particles that can form in aluminum alloys are very important in governing the pitting and localized corrosion properties of Al alloys. The determination of electrochemical properties of the phases is very important in terms of better understanding of corrosion behavior of the alloy which contain these intermetallics. Ag2AI intermetallic is the main precipitated phase in Aluminum-Silver system and preferentially precipitates in grain boundaries. To determine corrosion behavior of Ag2AI intermetalic with respect to Al matrix, the corrosion and pitting potential of Ag2AI intermetalic was investigated in 3.5 % NaCI solutions of different pH's. The results obtained from this study can be summarized as follow. 1. It has been observed that silver additions to aluminum up to 15 % Ag did not change significantly the pitting potential of aluminum. 2. Experimentally obtained pitting potentials of Al-Ag alloys is in accordance with the pitting potential values calculated theoretically from the model of Galvele, within ± 40 mV. IXPitting Behavior of A l-Ağ Alloys SUMMARY Aluminium and its alloys are a group of very important materials for engineering applications because of their lightness, malleability, resistance to corrosion, mechanical and physical properties. Since aluminum is a light and soft metal the additions of various alloying elements are necessary to improve its strength. VVhile strength is increased with alloying elements its corrosion resistance is decreased. This creates some problems during the use of aluminum alloys. To optimize strength and corrosion resistance of aluminum, another alloying elements are added to aluminum. Cu, Mn, Si, Mg, Zn, and Sn are used as primary alloying elements, besides these elements Li, Cr, Ni, Ağ, Zr, V, Ga, Ti, Pb, Co, Cd, Be, Bi are also added to aluminum alloys. The main aim of both majör and minör alloying is to improve mechanical and physical properties. Although silver has a significantly high solubility in aluminum and provides age hardenability in the alloy, it is not used as primary alloying element because of economic reasons. Hovvever recently, addition of low amounts of silver (< 1% Ağ), to the high strength Al alloys such as AI-Cu- Mg, AI-Zn-Mg and AI-Cu-Li are becoming increasingly popular. Silver changes significantly precipitation process in these alloys and improves strength. The use of silver as an alloying element in Weldalite-049 that was developed by NASA for space programs provided better understanding of the importance of silver in Al alloys. The studies on the effect of silver on the general and localized corrosion of aluminum were conducted with alloys having high silver content (10-20 %Ag). in the literatüre, there are no systematic studies on the corrosion of binary aluminum - silver alloys with low silver (up to 1 %Ag). Hovvever, it has been proposed that silver additions to AI-Cu-Mg and AI-Zn-Mg systems provided resistance to stress corrosion cracking and intergranular corrosion. in this investigation, the effect of silver on localized corrosion of aluminum was studied systematically in 3.5 % NaCI. in accordance with this objective, binary AI-Ag alloys with various contents of Ağ and AggAl intermetallic were prepared. Aluminum-Silver alloys and Ag2AI intermetallic were prepared from high purity materials (99.999 %AI, 99.99 % viIn galvanostatic experiments, programmable electrometer, Keithley 617, was added to potentiostatic experiment system. During the experiments 1 mA/cm2 current density was applied until a fixed potential obtained. When potential reached a fixed value current was interrupted in 3 seconds and then potential change was observed. During the experiments potential versus time data measured by the programmable electrometer. In these experiments, it has been found that silver additions to aluminum decreased anodic over voltage like copper, and did not change open circuit corrosion potential after certain values unlike copper (this value was approximately 0.9 % Ag). Therefore, it can be said that silver effected pitting behavior of aluminum by changing its open circuit corrosion potential in pit solution. In addition to performed experiments in saturated AICI3, to understand the effect of silver on corrosion behavior of aluminum in AICI3 solution better, anodic and cathodic polarization curves were obtained for pure aluminum, pure silver and some aluminum-silver alloys (0.02, 0.9, 5 % Ag) According to the results obtained from anodic and cathodic polarization curves, it has been understood that silver changed, unlike copper, corrosion potential of aluminum by accelerating especially the anodic reaction. Intermetallic particles that can form in aluminum alloys are very important in governing the pitting and localized corrosion properties of Al alloys. The determination of electrochemical properties of the phases is very important in terms of better understanding of corrosion behavior of the alloy which contain these intermetallics. Ag2AI intermetallic is the main precipitated phase in Aluminum-Silver system and preferentially precipitates in grain boundaries. To determine corrosion behavior of Ag2AI intermetalic with respect to Al matrix, the corrosion and pitting potential of Ag2AI intermetalic was investigated in 3.5 % NaCI solutions of different pH's. The results obtained from this study can be summarized as follow. 1. It has been observed that silver additions to aluminum up to 15 % Ag did not change significantly the pitting potential of aluminum. 2. Experimentally obtained pitting potentials of Al-Ag alloys is in accordance with the pitting potential values calculated theoretically from the model of Galvele, within ± 40 mV. IXPitting Behavior of A l-Ağ Alloys SUMMARY Aluminium and its alloys are a group of very important materials for engineering applications because of their lightness, malleability, resistance to corrosion, mechanical and physical properties. Since aluminum is a light and soft metal the additions of various alloying elements are necessary to improve its strength. VVhile strength is increased with alloying elements its corrosion resistance is decreased. This creates some problems during the use of aluminum alloys. To optimize strength and corrosion resistance of aluminum, another alloying elements are added to aluminum. Cu, Mn, Si, Mg, Zn, and Sn are used as primary alloying elements, besides these elements Li, Cr, Ni, Ağ, Zr, V, Ga, Ti, Pb, Co, Cd, Be, Bi are also added to aluminum alloys. The main aim of both majör and minör alloying is to improve mechanical and physical properties. Although silver has a significantly high solubility in aluminum and provides age hardenability in the alloy, it is not used as primary alloying element because of economic reasons. Hovvever recently, addition of low amounts of silver (< 1% Ağ), to the high strength Al alloys such as AI-Cu- Mg, AI-Zn-Mg and AI-Cu-Li are becoming increasingly popular. Silver changes significantly precipitation process in these alloys and improves strength. The use of silver as an alloying element in Weldalite-049 that was developed by NASA for space programs provided better understanding of the importance of silver in Al alloys. The studies on the effect of silver on the general and localized corrosion of aluminum were conducted with alloys having high silver content (10-20 %Ag). in the literatüre, there are no systematic studies on the corrosion of binary aluminum - silver alloys with low silver (up to 1 %Ag). Hovvever, it has been proposed that silver additions to AI-Cu-Mg and AI-Zn-Mg systems provided resistance to stress corrosion cracking and intergranular corrosion. in this investigation, the effect of silver on localized corrosion of aluminum was studied systematically in 3.5 % NaCI. in accordance with this objective, binary AI-Ag alloys with various contents of Ağ and AggAl intermetallic were prepared. Aluminum-Silver alloys and Ag2AI intermetallic were prepared from high purity materials (99.999 %AI, 99.99 % vi

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