Formation of Manganese-Containing PEO Coatings on Aluminum Alloys
337
experimental details are similar to that described in [17]. The indicators of catalytic
activity were the ignition temperature (T i ) and the conversion degree (X, %).
2 Peculiar Properties of PEO of Aluminum Alloys
in Alkaline Electrolytes
Properties of Al alloys essentially depend on the chemical composition and alloy
components/impurity elements ratio. Intermetallic compounds (IMC) of enough
various composition and amount (Table 2) presenting in aluminum alloys as
hardening phases in many respects cause a difference in their properties.
The change of alloy electrochemical properties is caused by pointed intermetallic
compounds localization in the surface layer. It is allowed for in parameter q i —the
specific surface area corresponding to the appropriate structure element localization. For example, it is known [19], that AA 2024-T alloy contain intermetallic
compound Al-Cu-Mg with the considerable proportion of surface area, therefore as
a first approximation it is possible to introduce such surface as
(AA 2024 − T3) s ≈ θ 1 (Al) + θ 2 (Al − Cu − Mg) + . . . + θ i (IMC),
or in limiting state:
θ (IMC) 0, θ(Al) > 0, θ(Cu) → 0, θ(Mg) → 0,
at invariable fulfillment of normality condition θ i = 1.
Manganese presence in the AMn alloy favorably influences its corrosionelectrochemical behavior due to the formation of intermetallic compounds with iron
Al 6 (Fe, Mn), AlFeSiMn, and others with enough negative electrode potential [19]. It
eliminates the contribution of the cathode sections of a corrosion process localized,
as a rule, on iron. However, at the common decrease of the surfaces hetero-resistivity,
there is a propagation of its reactive capacity. Therefore, the variation of aluminum
alloys and intermetallic compounds electrode potentials over a wide range (Table 3)
Table 2 The Intermetallic compounds in aluminum alloys [18, 19]
Alloy (ISO)
Intermetallic compounds
D16 (2024)
Hardening phases θ (Al 2 Cu) i S (Al 2 CuMg), intermetallic compounds
(Fe, Mn)
AMn (AlMn1Cu)
Al 2 Cu, Al 20 Cu 2 (MnFe) 3 , Al-Cu-Mg, Al-Cu-Mn–Fe
AL25
(AlSi12CuNiMg)
MnAl 6 , in Si and Fe presence—Al 6 (Fe, Mn), AlFeSiMn, α (AlFeSi)
337
experimental details are similar to that described in [17]. The indicators of catalytic
activity were the ignition temperature (T i ) and the conversion degree (X, %).
2 Peculiar Properties of PEO of Aluminum Alloys
in Alkaline Electrolytes
Properties of Al alloys essentially depend on the chemical composition and alloy
components/impurity elements ratio. Intermetallic compounds (IMC) of enough
various composition and amount (Table 2) presenting in aluminum alloys as
hardening phases in many respects cause a difference in their properties.
The change of alloy electrochemical properties is caused by pointed intermetallic
compounds localization in the surface layer. It is allowed for in parameter q i —the
specific surface area corresponding to the appropriate structure element localization. For example, it is known [19], that AA 2024-T alloy contain intermetallic
compound Al-Cu-Mg with the considerable proportion of surface area, therefore as
a first approximation it is possible to introduce such surface as
(AA 2024 − T3) s ≈ θ 1 (Al) + θ 2 (Al − Cu − Mg) + . . . + θ i (IMC),
or in limiting state:
θ (IMC) 0, θ(Al) > 0, θ(Cu) → 0, θ(Mg) → 0,
at invariable fulfillment of normality condition θ i = 1.
Manganese presence in the AMn alloy favorably influences its corrosionelectrochemical behavior due to the formation of intermetallic compounds with iron
Al 6 (Fe, Mn), AlFeSiMn, and others with enough negative electrode potential [19]. It
eliminates the contribution of the cathode sections of a corrosion process localized,
as a rule, on iron. However, at the common decrease of the surfaces hetero-resistivity,
there is a propagation of its reactive capacity. Therefore, the variation of aluminum
alloys and intermetallic compounds electrode potentials over a wide range (Table 3)
Table 2 The Intermetallic compounds in aluminum alloys [18, 19]
Alloy (ISO)
Intermetallic compounds
D16 (2024)
Hardening phases θ (Al 2 Cu) i S (Al 2 CuMg), intermetallic compounds
(Fe, Mn)
AMn (AlMn1Cu)
Al 2 Cu, Al 20 Cu 2 (MnFe) 3 , Al-Cu-Mg, Al-Cu-Mn–Fe
AL25
(AlSi12CuNiMg)
MnAl 6 , in Si and Fe presence—Al 6 (Fe, Mn), AlFeSiMn, α (AlFeSi)