Metastable phases and microstructure of a rapidly solidified Al-Li-Mn-Zr alloy for high temperature applications

A new Al-Li alloy, containing 2.5 wt.% Li, 6.5 wt.% Mn and 0.80 wt.% Zr, for high-temperature applications, has been processed by rapid solidification techniques (as powders by ultrasonic gas atomization and as compacts by spray deposition), and then thermomechanically treated by HIP and Hot extrusion. The as-received deposits and powders (of various size fractions) were characterized by X-ray diffraction and by SEM/EDAX. Measurements of the lattice parameter of the αAl phase revealed a direct relationship between the degree of excess solubility of Mn in Al and the cooling rate during solidification. Phase analyses show the presence of two Mn phases (Al4Mn and Al6Mn), that could reduce the amount of soft precipitate free zones in the matrix, one Zr phase, (Al3Zr), that would contribute to dispersoid hardening and to inhibition of recovery and recrystallization, and two Li phases (the stable AlLi and the metastable Al3Li), probably affecting solution hardening and aging characteristics.