Structure and properties of a rapidly solidified Al-Li-Mn-Zr alloy for high-temperature applications: Part II. spray atomization and deposition processing

A new Al-Li alloy containing 2.3 wt pct Li, 6.5 wt pct Mn, and 0.65 wt pet Zr for high-temperature applications has been processed by a rapid solidification (RS) technique (as compacts by spray atomization and deposition) and then thermomechanically treated by hot extrusion. As-received and thermomechanically treated deposits were characterized by X-ray diffraction and scanning electron microscopy (SEM). Phase analyses in the as-processed materials revealed the presence of two Mn phases (Al₄Mn and Al₆Mn), one Zr phase (Al₃Zr), two Li phases (the stable AlLi and the metastable Al₃Li), and the aAl solid solution with high excess in Mn solubility (up to close the nominal composition in the as-atomized powders). As-deposited and extruded pieces were given heating treatments at 430 °C and 530 °C. A two-step aging treatment was practiced, to check for the optimal (for tensile properties) aging procedure, which was found to be the following: solutioning at 430 °C for 1 hour and water quenching + a first-step aging at 120 °C for 12 hours + a second-step aging at 175 °C for 15 hours. The mechanical properties, at room and elevated temperatures, of the hot extruded deposits are compared, following the optimal solutioning and aging treatments. The room-temperature (RT) strength of the proposed alloy is distinctly better for the as-deposited specimens (highest yield strength, 320 MPa) than for the as-atomized (highest yield strength, 215 MPa), though less than 65 pct of the RT strength is conserved at 250 °C. Ultimate strengths are quite comparable (in the 420 to 470 MPa range). Ductilities at RTs are in the low 1.5 to 2.5 pct range and show no improvement over other Al-Li alloys.