Effects of eutectic modification and T4 heat treatment on mechanical properties and corrosion resistance of an Al-9Â wt%Si casting alloy

It has been reported that the mechanical properties and the corrosion resistance of metallic alloys depend strongly on the final microstructural arrangement. In order to achieve a desired level of final properties, the correlation of microstructural parameters with corrosion behavior and mechanical properties can be very useful for planning the manufacturing process. The aim of the present work was to investigate the influence of microstructural parameters of an Al-9 wt%Si alloy in as-cast, modified (eutectic) and heat-treated conditions on the resultant mechanical properties and corrosion resistance. Experimental results include ultimate tensile strength, yield strength, hardness, electrochemical impedance parameters and corrosion rates. Corrosion behavior was evaluated by both the electrochemical impedance spectroscopy technique and by Tafel plots carried out in a 0.5 M NaCl test solution at 25 °C. The impedance parameters were obtained from equivalent circuits provided by the ZView software. It was found that the ultimate tensile strength increases both with the addition of a eutectic modifier and with the T4 heat treatment. Yield strength seems to be independent of such processes. On the other hand, it was also found that the corrosion resistance has significantly decreased with the eutectic modification. The T4 heat treatment has provided a recovery on the corrosion resistance.