Vacancy-type defects study on ultra-fine grained aluminium processed by severe plastic deformation

Vacancy-type defects play an important role in the metal materials deformed by severe plastic deformation (SPD). The present work use positron annihilation lifetime spectroscopy (PALS) to test the vacancy-type defects in aluminium alloys processed by equal channel angular pressing (ECAP) and accumulative roll bonding (ARB). ECAP at room temperature and cryogenic temperature was conducted to AA1050 and ARB with 200 C preheating was conducted to AA1050 and AA6061 to produce laminated AA1050 sheets, AA6061 sheets and AA1050/AA6061 composites. High fraction of vacancy-type defects were detected in all the deformed samples. Vacancies associated with dislocations and bulk mono-vacancies have been identified in RT-ECAP deformed samples. Three types of vacancy-type defects, vacancies associated with dislocations, bulk mono-vacancies and bulk di-vacancies, have been identified in the CT-ECAP processed samples. The ARB process is more efficient in grain refinement and strengthening. However, the accumulation of vacancy-type defects in ARB deformation seems less efficient. Vacancies associated with dislocations are the major vacancy-type defects for ARB processed AA1050 sheets but there exist some bulk mono-vacancies. However, most of the vacancy-type defects in the ARB processed AA6061 are vacancies associated with dislocations. A very small fraction of bulk mono-vacancies can be extracted but it is so small that it can be neglected. The lifetimes of ARB processed AA1050/AA6061 composites are generally in between the values of AA1050 sheets and AA6061 sheets. Voids were not detected in neither of the samples.