ANODIC-DISSOLUTION CHARACTERISTICS OF AL2 CU INTERMETALLIC COMPOUND IN DILUTE HCLO4 SOLUTION

The anodic dissolution characteristics of Al2Cu intermetallic compound s which is stoichiometric or Al-rich specimens are investigated by the measurements of an electrochemical method such as anodic polarization curves and potentiostatic dissolution tests, immersed corrosion tests and scanning electron microscopic observations of corroded surfaces f or the specimens in a dilute HClO4 solution. The main results obtained are summarized as follows: (1) The anodic polarization curves of Al2C u intermetallic compound specimens in a dilute HClO4 solution show a t ypical active-passive transition, and the limiting anodic current dens ity of the specimens increases with an increase in the concentration o f HClO4 and the solution temperature irrespective stoichiometries of t he specimens. However, the anodic dissolution rate of the Al-rich spec imen is larger than that of stoichiometric ones under the same conditi ons. (2) The activation energies of anodic dissolution of Al2Cu are 27 .6 kJ/mol for the Al-rich specimen and 48.5 kJ/mol for the stoichiomet ric ones. (3) The proposed anodic dissolution mechanism for Al2Cu inte rmetallic compound specimens in the dilute HClO4 solution under the po tentiostatic condition is shown in the following equations: The select ive anodic dissolution of Al species from the stoichiometric Al2Cu int ermetallic compound: (1)Al2Cu(s) --> 2Al((aq.))(3+)+Cu-(s)(0)+6e(-) (2 )Al2Cu(s) --> Al-(aq.)(3+) +AlCu(s)+3e(-) The selective anodic dissolu tion of Al species from the eutectic phase in the Al-rich Al2Cu interm etallic compound specimen: Al2Cu+Al(in solid solution)+Cu(in solid sol ution)--> (3)Al-(aq.)(3+)+Al2Cu(s)+Cu-(s)(0)+3e(-)