アルミニウム金属間化合物の電気化学的性質とアルミニウム合金の腐食形態の関係

抄録

The corrosion potentials of binary aluminum alloys (Al-0.5% Fe, Al-0.5% Ni, Al-0.5% Mn and Al-4% Cu) and the polarization curves of pure aluminum (99.999% Al) and aluminum intermetallic compounds (Al₃Fe, Al₃Ni, Al₄Mn and Al₂Cu) have been measured in 1 mol solutions of H₂SO₄, NaCl, Na₂SO₄ and NaOH. The binary alloys were heat-treated at proper temperatures in order to precipitate intermetallic compounds, so that the resulting phases are the aluminum matrix and intermetallic compounds. The corrosion morphology of the alloys containing a small amount of intermetallic compounds was discussed on the basis of the differences between the dissolution rates of pure aluminum and the intermetallic compounds at the potentials coresponding to the corrosion potentials of the binary alloys.
The corrosion morphology of the binary alloys tested can be classified into the following four types according to the kinds of solutions used: (1) The intermetallic compounds are attacked preferentialy with an acid solution, (2) the intermetallic compounds undissolved remain on the specimen surfaces in an alkaline solution, (3) the pitting corrosion breaks out around the intermetallic compounds in a neutral solution with chloride ions and the intermetallic compounds will remain in corrosion pits because the dissolution rate of these compounds is lower than that of the pitting corrosion of the matrix phase, and (4) no apparent changes by corrosion occur in a neutral solution without chloride ions because of the very small dissolution rates of both the matrix and the intermetallic compound phases.