Pitting Corrosion of Cast Metallurgy Aluminum-Beryllium Alloys in Sulfuric Acid Solutions

Abstract

Abstract Four casting alloys of aluminum-beryllium ranging in a Be composition from 15 wt% to 68 wt% were tested in sulfuric acid (H2SO4) solutions of pH 2 and 4. Cyclic potentiodynamic polarization tests of the Al-Be alloys demonstrated passive behavior and positive hysteresis. Following cyclic polarization testing, all alloys showed preferential corrosion of the Be-rich phase in the forms of pitting or phase boundary attack with evidence of crystallographic etching. Total pit surface area in the Be phase was proportional to the volume fraction of the Al phase. Immersion test specimens showed uniform corrosion of the Al phase at pH 4, while the Be phase showed phase boundary and crystallographic attack at pH 2. Corrosion potentials were most noble for alloys with the highest Be wt% while corrosion current density decreased with Be wt%. A lower pH increased the corrosion rate for all alloys.