Influences of strain rate and grain size on yield and serrated flow in commercial Al-Mg alloy 5086

Abstract

The deterioration in surface quality due to the formation of Lüders lines is a typical phenomenon in 5xxx series Al–Mg alloys. Traditional efforts show that an increase of the grain size results in the suppression of the Lüders elongation. This paper presents that the suppression of the Lüders elongation can be realized at a smaller grain size by the addition of Zn/Cu elements in the 5xxx series alloys and by pre-aging treatment. The alloys with (Zn + Cu)/Mg ratios below 1.0 result in an increase of the strength by the precipitation of T-Mg32(AlZnCu)49 phase, and quite different from 7xxx series Al–Zn–Mg alloys strengthened by η-MgZn2 precipitates. The decisive measurement for suppressing Lüders elongation is based on the depletion of Mg atom concentrations in the matrix due to the formation of GP zones after pre-aging treatment.