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 melt-spinning to produce ribbons between 35 and 70 μm thick. Microstructures were of the classical zone A/zone B type with a notable increase in αAl 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 °C gave significant hardening at 200 and/or 300 °C for all of the more concentrated alloys, the largest responses being produced by Al-6.3 at % Y and Al-4.2 at % La at 200 °C. X-ray diffraction asspun indicated the presence of only αAl and equilibrium Al₁₁La₃ in the Al-La alloy ribbons and αAl and a non-equilibrium Al₄Y/Al₁₁Y₃ in the Al-Y ribbons. This non-equilibrium Al-Y phase was identified by X-ray diffraction as isomorphous with orthorhombic or tetragonal Al₁₁ La₃ 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 network with Energy dispersive spectroscopic analysis indicating an average composition Al-46 wt% Y consistent with the Al₄Y/Al₁₁Y₃ stoichiometry and diffraction patterns consistent with an orthorhombic or tetragonal cell with these lattice parameters. While no significant change in phase constitution of the Al-La ribbons was detected by X-ray diffraction as a result of heat treatment, the Al₁₁Y₃ in Al-Y ribbons was seen to be replaced by βAI₃Y on heat treatment at 400 and 500 °C.