An Accelerated Bulk Immersion Surrogate for ASTM B117 Corrosion Testing for Secondary A356-T6 (AlSi7Mg0.3) Al Alloy Low-Pressure Die Castings

This work developed an accelerated bulk immersion surrogate that reproduces the corrosion mode and extent exhibited by secondary A356-T6 (AlSi7Mg0.3) Al alloy samples made by the low-pressure die castings process after 1000 h of ASTM B117 continuous salt fog exposure. The accelerated test will be used to determine the effect of pre-corrosion on the uniaxial tensile properties including strength and ductility (elongation) in an expedited manner. The corrosion mode exhibited after 1000 h of ASTM B117 exposure was interdendritic with the eutectic Al phase serving as the anode and the eutectic Si phase serving as the cathode and without any significant attack of the primary Al matrix. Of the various bulk immersion surrogates tested (with and without electrochemical polarization), the one involving 96 h of bulk immersion in 5% NaCl (aq) + an initial addition of 30% H2O2 (aq) (9 mL in 1000 mL) at 35 °C under open-circuit conditions was most successful.