Stress relaxation in Al alloys of Al-Mg-Mn, Al-Mg-Se and Al-Mg-Li-systems

The paper deals with the investigation results of stress relaxation in deformed semiproducts from AL-alloys of AL-Mg-Mn, AL-Mg-Sc, AL-Mg-Li- systems during their heating from 70 to 210 degrees C and exposure up to 500 hrs. It was established that on the stretcher straightening the compression (up, to 180 Mpa) and on the cold rolling the tensile (up to 80 Mpa) stresses occur in specimens. In nonheat-treatable alloys of AL-Mg-Mn, AL-Mg-So, AL-Mg-Li- systems the resudial stresses at 70 degrees C for 100 hrs are 60-80% whereas at 120 degrees C - 10-30%. In heat-tretable AL-Mg-Li-alloys the higher level (50%) of residual stresses is retaind on heating at temperature above 120 degrees C. Scandium in combination with zirconium hamper the diffusion mobility in the aluminium solid solution at 70 to 120 degrees C to the greater degree than the manganese does and so decrease the stress relaxation rate.