Corrosion behavior of A 356 Al alloy in acid rain

The open circuit potential for A 356 Al alloy and its composites prepared by vortex and squeeze casting techniques increases in noble direction with time indicating growth of the air formed passive film on the tested materials in the acid rain. The polarization results revealed that the addition of zirconia up to 20% to A 356 Al alloy increases its corrosion resistance but when this content increases to 30% this corrosion resistance decreases slightly but still very high than that of the unreinforced A 356 alloy. Also, the values of the corrosion rate for the squeeze composites are lower than that for vortex cast composite of the same percentage of zirconia. the squeeze cast alloys have high corrosion resistance than the vortex cast ones due to the first ones contain low porosity than the vortex ones. The SEM micrographs showed that for the vortex composite contains 20% ZrO2 and squeeze one contains 5% ZrO2 at 50 MPa protective passive films include much less very minor pits were formed on their surfaces. Additionally, The EDS spectra conformed that the films grew on the vortex and squeeze composites consist of aluminium oxide.