The origin of softening in predeformed metals

One of the main limitation in industrial sheet metal working processes is t he appearance of plastic instability phenomena that reduce the ductility an d promote premature failures of the material. Instabilities are amplified b y flow softening and both textural and structural processes may be responsi ble for the decrease of the stress level. The purpose of the present work i s to analyse the importance of these two mechanisms on the formability of l ow carbon steel and aluminium 1050 alloy. The two metals were prestrained b y rolling and then reloaded in simple shear mode. Structural evolutions are determined by transmission electron microscopy while textural changes are estimated by X-rays measurements. Viscoplastic self-consistent calculations were used to correlate the texture evolution during reloading with the wor k-hardening behaviour. For the low carbon stell the presence of microbands after reloading reveals a structural destabilisation. For aluminium the pla stic instability are associated with the texture evolution.