STRUCTURE, PROPERTIES AND RESPONSE TO HEAT-TREATMENT OF MELT-SPUN AL-Y AND AL-LA ALLOYS

Al-Y and Al-La binary alloys containing 0.7-18 wt% (0.2-6.3 at%) Y and 0.9-18 wt% (0.2-4.2 at%) La, were rapidly solidified by chill-block m elt-spinning to produce ribbons between 35 and 70 mum thick. Microstru ctures were of the classical zone A/zone B type With a notable increas e in alphaAl lattice parameter for the Al-6.3 at% Y composition, which exhibited a Knoop hardness of 430 +/- 30 kg mm-2 as-spun. Isochronal ageing for 2 h at 200-500-degrees-C gave significant hardening at 200 and/or 300-degrees-C for all of the more concentrated alloys, the larg est responses being produced by Al-6.3 at%Y and Al-4.2 at% La at 200-d egrees-C. X-ray diffraction as-spun indicated the presence of only alp haAl and equilibrium Al11La3 in the Al-La alloy ribbons and alphaAl an d a non-equilibrium Al4Y/Al11Y3 in the Al-Y ribbons. This non-equilibr ium Al-Y phase was identified by X-ray diffraction as isomorphous with orthorhombic or tetragonal Al11La3 with lattice parameters determined as a(o) = 0.42 +/- 0.02 nm (b(o) = 1.26 +/- 0.06 nm) and c(o) = 0.97 +/- 0.05 nm. TEM showed that it was present as an intercellular networ k with Energy dispersive spectroscopic analysis indicating an average composition Al-46 wt% Y consistent with the A14Y/Al11Y3 stoichiometry and diffraction patterns consistent with an orthorhombic or tetragonal cell with these lattice parameters. While no significant change in ph ase constitution of the Al-La ribbons was detected by X-ray diffractio n as a result of heat treatment, the Al11Y3 in Al-Y ribbons was seen t o be replaced by betaA13Y on heat treatment at 400 and 500-degrees-C.