Rapidly solidified Al-Mo and Al-Mn ribbons: microstructure and mechanical properties of extruded profiles

Two alloys of composition Al-Mo(3; 5) at.% and Al-Mn(3; 5) at.% were studied in the form of compacted cuts of rapid solidification ribbons. The structure of samples was composed of fcc alpha-Al solid solution oversaturated with Mo and Mn, intermetallic Al12Mo and Al6Mn phases, all in ultrafine submicron grain size. The kinetics of structural changes and their effect on mechanical properties were described as a function of annealing temperature and time. The discrete RS particles (chopped ribbons) were compacted into simple structural profiles using conventional and relatively inexpensive direct extrusion method. All compacted profiles exhibited similar structure as precursor materials, incl. even grain size. Almost theoretical density with no identified porosity and gas entrapment was achieved. The extruded profiles were extremely thermally stable; no structural changes were detected even after annealing at 300 degrees C for 24 h. The best mechanical properties were obtained for compacted RS A1Mo5 ribbons: their UTS at room temperature exceeded 385 MPa at 5 % elongation to fracture. UTS at 300 degrees C/24 h regularly exceeded 375 MPa what is 5 times higher than UTS of conventionally used Al alloys. Young's modulus (B) of extruded compact at RT was 90 GPa what means an increase of more than 25 % in E/rho compared with standard Al.