NONDESTRUCTIVE EVALUATION OF PLASTIC-DEFORMATION IN AA6061 ALUMINUM-ALLOY BY ELECTROMAGNETIC DISCHARGE IMAGE

The electromagnetic discharge imaging (EDI) technique is combined with image analysis methods and used as a nondestructive method to evaluat e the amount of plastic deformation of AA6061 aluminum alloy. Various amounts of plastic deformation was introduced mechanically by cold rol ling on specimens having identical surface conditions to the specimen. Since the EDI discharge characteristics and intensity are affected by plastic deformation, the results can be used as a correlation. It is shown that the EDI discharge intensity increases with increasing rolli ng ratio up to 25% and reaches a saturation limit, beyond which the di scharge intensity is inversely proportional to the rolling ratio. Sinc e the changes of the internal energy and the electrical properties of the specimen caused by cold rolling has opposing effects on the EDI di scharge intensity. That would eventually be saturated. Further analysi s shows that the high intensity region of EDI discharge pattern is inc reased from 0-10% rolling ratio and then from 30% and up. As the AC fr equency increased, the discharge intensity becomes proportional to the increase rolling ratio. (C) 1997 Elsevier Science Ltd.