SEDL / STP / STP890-EB / STP33027S

Al³Li Precipitate Modification in an Al-Li-Zr Alloy

Gayle, FW
Graduate student and professor of materials science, Massachusetts Institute of TechnologyReynolds Metals Co., CambridgeRichmond, MAVA

Vander Sande, JB
Graduate student and professor of materials science, Massachusetts Institute of TechnologyReynolds Metals Co., CambridgeRichmond, MAVA

Pages: 17    Published: Jan 1986

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Abstract

An Al-2.34Li-1.07Zr (weight percent) alloy was produced using rapid solidification processing in an attempt to modify the δ′ (Al³Li) precipitate found in the Al-Li binary system to a complex Al³(Li,Zr) phase. Such a modification is expected to increase fracture toughness and ductility by decreasing shear localization, which is a major drawback in Al-Li alloys. A novel microstructure is presented in which a zirconium-rich phase present as fine spheres or discontinuously precipitated rods (with diameters of 6 to 20 nm) is subsequently enveloped by δ′ during aging at 190°C.

Electron diffraction effects, energy-dispersive X-ray analysis in scanning transmission electron microscopy, and preliminary electron energy loss spectroscopy results indicate that the precipitate phase stable at 500°C is Al³(Li^x,Zr^1−x), where x appears to be 0.45 to 0.8. This is in contrast to the Al-Li and Al-Zr binary systems, in which the equilibrium phases at 500°C for these solute levels are aluminum solid solution and Al³Zr in an aluminum matrix, respectively. The alloy shows longitudinal strength-ductility combinations which are significantly better than those of a low-zirconium control alloy and which compare quite favorably with those of other Al-Li alloys.