The microstructural characteristics of AI-Cu-Li-Mg-Zr alloys have been studied after rapid solidification by melt spinning and after subsequent annealing at temperatures in the range 160 to 500°C, by using a combination of optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and microhardness measurements. The as-melt-spun alloys consist of a cellular microstructure with fine scale δ′ precipitates and icosahedral particles distributed within the cells and at cell boundaries. The icosahedral structure is equivalent to the T2 phase reported by Hardy and Silcock. Annealing the melt-spun alloys leads to a complex precipitation sequence: α + I +δ → α + I + S′ +θ′ → α + I → α +δ′ + T1 + T2 (bcc) + two other phases. The icosahedral particles coarsen progressively during annealing, especially at higher annealing temperatures. Fine-scale δ′ precipitates grow during annealing at low temperature, dissolve at higher annealing temperatures below 500°C, and then reprecipitate during cooling after annealing at 500°C. During annealing at low temperature, plates of θ′ and S′ precipitate and then dissolve, providing solute atoms for icosahedral particle growth. Stable T1, T2 (bcc) and two other phases precipitate after decomposition of the icosahedral particles during annealing at 500°C.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering