1991 Volume 55 Issue 4 Pages 360-365
The quench sensitivity of an 8090 (Al-Li-Cu-Mg-Zr) alloy was evaluated by adopting heat-treatment including step-quenching followed by aging. It was confirmed that the quench sensitivity of the 8090 alloy was quite low compared with that of the other age-hardenable aluminum alloys. In other words, the age-hardenability of this alloy was hardly lowered by slow cooling from solution-treatment temperatures. This was ascribed to the fact that almost all dispersoids of an Al3(Zr, Li) phase were still coherent after solution-treatment, since coherent dispersoids never act as the heterogeneous nucleation site for incoherent stable phases during slow cooling. The dispersoids maintained their coherency, because no recrystallization occurred in the cold-worked specimens. This was probably due to the fact that the volume fraction of the dispersoid was high enough on account of Li-bearing. In addition, most of the dispersoids were found to remain coherent even in a specially recrystallized region because of the occurrence of dissolution and reprecipitation of the dispersoids. The reason was discussed why the dissolution was possible only in this alloy and not in Al-Zn-Mg-Cu-Zr alloys, when high angle boundaries were in contact with the Zr-bearing dispersoids.
