Corrosion Behavior of Extruded near Eutectic Al-Si-Mg and 6063 Alloys

In this work, a comparison study on corrosion behavior of extruded near eutectic Al-12.3%Si-0.26%Mg and 6063 alloys has been carried out by mass loss test in 4% H2SO4 aqueous solution in the open air and potentiodynamic polarization test in 3.5 wt.% NaCl aqueous solution. Results indicate that the corrosion resistance of the near eutectic Al-Si-Mg alloy is less than that of 6063 alloy. Macro/microscopy and scanning electron microscopy results clearly show the difference of the corrosion progress of these two alloys in 4% H2SO4 aqueous solution. The corrosion type of 6063 alloy is pitting corrosion. The Mg2Si and AlFeSi particles and surface defects act as nucleation sites for pitting, and the amount and distribution of them have a significant effect on the pitting behavior. For the near eutectic alloy, there are two types of corrosion cells. One is between the extruded primary alpha-Al and the eutectic, the other is between the eutectic Al and eutectic Si particles. Combination of these two types of corrosion cells leads to a lower corrosion resistance, a higher mass loss of the near eutectic alloy compared with 6063 alloy, and the formation of the paralleling corroded grooves.