Evolution of discontinuous/continuous Al3(Sc,Zr) precipitation in Al-Mg-Mn 5083 alloy during thermomechanical process and its impact on tensile properties

The evolution of discontinuous and continuous Al3(Sc,Zr) precipitation in an Al-Mg-Mn AA5083 alloy during heat treatment and hot rolling was investigated. The results showed that, at a high Sc content (0.43 wt%), a large number of line/fan-shaped structures were formed as discontinuous Al3(Sc,Zr) precipitation during solidification, while no such discontinuous precipitation was observed when the amount of Sc added was low (0.15 wt%). During the three-step heat treatment (275 C /12 h + 375 C/48 h + 425 C/12 h), two types of precipitates - Mn-bearing dispersoids and spherical Al3(Sc,Zr) precipitates - were formed as the main strengthening phases. In the high-Sc alloy, the discontinuous Al3(Sc,Zr) precipitates dissolved partially. However, the quantity of the spherical Al3(Sc,Zr) precipitates in the high-Sc alloy was much lower than that in the low-Sc alloy, which degraded its aging hardening response. During hot rolling, although the discontinuous precipitates were completely dissolved, the number density of the spherical Al3(Sc,Zr) precipitates in the high-Sc alloy was still lower than that in the low-Sc alloy. The tensile properties of the Sc-containing alloys improved significantly compared with those of the base alloy. However, the yield and ultimate tensile strengths of the high-Sc alloy were lower than those of the low-Sc alloy. This indicates that the discontinuous precipitation had a deleterious effect on the mechanical properties of the alloy.