The effect of scandium on the as-homogenized microstructure of 5083 alloy for extrusion

The microstructure of 5083 alloys, standard and modified by Sc, before/after homogenizing heat treatment were examined. The optimum condition for homogenizing heat treatment and the effect of Sc were discussed. In the results of this study, the microstructure of the 5083 alloys was improved largely by the addition of Sc. As for the cast structure, DAS (dendrite arm spacing) was considerably decreased. The intermetallic compounds formed between dendrite arms became smaller in Sc modified 5083. In ordinary 5083 and Sc modified 5083 alloys, the area fraction of intermetallic compounds approaches the minimum at the homogenizing temperature around 520 degrees C. Detailed analysis regarding the composition of existing intermetallic compounds, shows that the Sc added is mostly utilized in the Al3Sc phase, not in the intermetallic compounds other than Al3Sc. These favorable effects of modification by Sc are considered to come mainly from the fine, uniform distribution of the coherent and spherical Al3Sc precipitates. (C) 2000 Elsevier Science S.A. All rights reserved.