Influence of thermal and surface treatments on distributions of lead in Al-Pb foils

Thr effects of heat-treatment, electropolishing, alkaline etching, and anod izing on the distributions of lead in 100 mu m thick, two-phase aluminium f oils, containing 100, 500 1000,;md 10,000 ppm le;lead, have been examined b y scanning electron microscopy and Rutherford backscattering spectroscopy. Heat-treatment at 823 K for 20 ks resulted in segregation of similar to 3 t o 15% of the lend to within approximately 500 nm of the surfaces of the foi ls. The enrichments, dependent upon foil composition, were largely retained in the near-surface regions during subsequent alkaline etching. but electr opolishing caused depletion of lead. with respect to the bulk composition, over a depth up to about 500 nm, associated with loss of lead-rich particle s, No significant enrichments were developed during subsequent anodizing of electropolished foils. In contrast, following anodizing of etc foils, lead was enriched both in the metal layers immediately adjacent to the metal/an odic: film interfaces and at the surfaces of the anodic films. Further, lea d oxide or hydroxide particulates associated with anodic oxidation of lead particles, decorated the foil surfaces. It is suggested that lead species a re present throughout anodic film material formed above matrix regions of m etal. where they migrate outward faster than Al3+ ions to form a layer of l ead-rich oxide at the film/electrolyte interface. The anodizing process res ulted in loss of roughly 50% of the of original enrichment of the etched fo il. (C) 2000 The Electrochemical Society. S0013-4651(99)06-069-3. All right s reserved.