Effect of silicon content on the corrosion behavior of AL-SI piston alloys in some aqueous media

1- The corrosion behavior of AI-Si alloys in aqueous solution resulting from condensed part of the exhaust on the piston head is complex. It depends on the pH, anion type and alloy composition.2- The eutectic alloy with 11.2% Si showed the highest corrosion rate due to its relatively fine grained structure and its high surface energy.3- The hypoeutectic alloys (1% Si and 8% Si) and hypereutectic alloy (15% Si) corrode in aqueous media less than eutectic alloy (11.2% Si). This may be due to presence ofelemental silicon or aluminum each causes stabilization of oxide film on the alloy surface.4- Shift of the OCP to more noble values with both simulated condensate (pH=3.5) and H2S04 (pH=3.7) electrolytes as compared with electrolytes cpntaining•Fe203 (pH=7.75) or Ah03 (pH=7.4) particles as well as the 10/0 NaCI electrolyte may be ascribed to the difference in the pH values of these electrolytes.5- The high degree of attack of simulating condensate solution of fuel combustion products may be due to its higher acidity (pH=3.5), compared with the other test electrolytes containing alumina or ferric oxide as well as that of 1 % NaCI electrolyte.6-H2S04 electrolyte has the highest effect on the corrosion rate as compared with other constituent in simulated condensate electrolyte7- The range of re-passivation potential Increases with mcrease of silicon content in the alloy.8- Both the corrosion rate and frequency of current oscillations increased remarkably with increasing stirring.9- Upon increasing stirring rotation speeds, the corrosion potential was shifted to more noble value.10- The relatively severe corrOSion rate at high stirring rotation speed in simulated condensate solution can be ascribed to the removable of the passive film under erosive action of AhO) and FezOJ particles.