Structure, properties and response to heat treatment of melt-spun Al-Y and Al-La alloys
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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 ao = 0.42 ± 0.02 nm (bo = 1.26 ± 0.06 nm) and co = 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.
KeywordsHeat Treatment Binary Alloy Energy Dispersive Spectroscopic Analysis Average Composition Notable Increase
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