Improving Corrosion Resistance of Al through Sever Plastic Deformation 1-under Free Condition

THE CORROSION rate of Al in 3.5 % NaCl at room temperature can be reduced by subjecting the metal to sever plastic deformation (SPD) through the procedure of surface mechanical attrition treatment (SMAT).  The corrosion resistance of grain refined Al in 3.5% NaCl by SMAT for 5, 10, 15, 20 and 25 min in comparison with Al as rolled(0) and after annealing for 5 hr at 600 ^◦C (blank) was investigated by open circuit potential measurement. The results show that as increasing the time of SMAT up to 15min, the steady state potential (E_st.) shifted to less negative values. In contradiction, further increasing the time to 20 and 25 min, the potential returned to more negative values. Surface examination using scanning electron microscope (SEM), electron dispersive X-ray (EDX) and X-ray diffraction (XRD) proved that the above results are controlled by the time of oxide film formation. This depends on different factors such as the grain refinement, the segregation of Fe to the outer surface, the formation of micro cavities, the crystallographic orientation and habit Al (111) plane phases.