Characterization of Lead Enrichment on Electrochemically Active AlPb Model Alloy

Abstract

Certain com. Al alloys can become electrochem. activated by heat-treatment of enrichment of the trace element Pb at the surface. For a better understanding of the nature of activation, Pb enrichment resulting from annealing for 1-24 h at 300-600° in air, followed by quenching in H2O, was studied on an AlPb binary model alloy, using electrochem. polarization, electron optical techniques, and glow discharge optical emission spectroscopy. Most of the enriched Pb is near the oxide film-Al matrix interface, probably in solid soln. with Al. The surface concn. reached an apparent satn. level of 0.8% at 600°, up from 20 ppm in the bulk. Segregated metallic Pb particles were detected at an increasing d. and size with increasing time of annealing at 600°. However, segregation of Pb particles did not have an appreciable effect on activation. It is suggested, therefore, that the electrochem. activation is related to reduced passivity of the overlying oxide by Pb enriched in solid soln. at the metal surface and ensuing pitting potential depression in the combined presence of aggressive chloride ions in the test soln. [on SciFinder(R)]