Deposition of Metals on Aluminum by Immersion from Solutions Containing Fluorides

Abstract

A new process has been developed for depositing zinc, cadmium, and tin by chemical displacement upon aluminum. The immersion solutions contain the metal sulfate and either hydrofluoric acid or the fluoride anion. The deposited metals have good appearance, sound structure, and excellent adhesion to the aluminum, which does not depend on any roughening of the aluminum surface. The bond between the zinc deposit and aluminum is the best of the metals deposited and is greater than the cohesive strength of the aluminum base metal. The zinc immersion deposit may thus be used as a base for plating other metals. The effectiveness of the method results from the extraordinarily high solubility of the oxide film on the aluminum in solutions containing the fluoride anion in acid environment. This is shown from published solubility data and is demonstrated by potential measurements.