Ultralow-Density, High-Modulus, and High-Strength RSP Al-Li-Be Alloys

Abstract

Aluminum-lithium-beryllium alloys have been prepared by melt spinning, using prealloyed arc-melted buttons. The alloy ribbon was comminuted and cold compacted to 30 to 50% density, vacuum hot pressed to 100% density, and extruded. The bar product was subsequently solution heat treated, quenched, and aged. The microstructure of the alloys consists of a relatively featureless matrix containing a homogeneous dispersion of fine beryllium particles, mostly 50 to 500 nm in size. The results of heat treatment show that the alloys respond to age hardening in a manner similar to that of binary Al-Li alloys. Preliminary results on the mechanical properties and their relationships with microstructural features are presented for the Al-Li-Be alloys, as well as their potential for weight savings. The authors estimate that these monolithic aluminum alloys may exhibit specific strength and elastic modulus values comparable to those of the best whisker or particulate metal-matrix composites, while showing concomitant high weight savings.

Microstructural evaluation of rapidly solidified Al-Li-Be alloys

“…Two alloys (A1-3Li-2Be and A1-3Li-10Be by wt %) were converted to melt-spun ribbon using equipment designed and built at the Lockheed Palo Alto Research Laboratory [1]. Ribbon of approximate dimensions 1 to 2 mm in width and 20 to 70/~m thickness was produced.…”

“…The rationale for the development of ternary AI-Li-Be alloys has been presented recently by Lockheed scientists [1,2]. It was shown that such alloys could have important applications for aerospace structures because of their high potential weight savings.…”

“…The production of wrought A1-Li-Be alloys by conventional ingot casting having useful engineering properties is not possible [1,2]. This is because beryllium segregates in a coarse distribution upon freezing, and this results in poor ductility and toughness.…”

“…In RSP aluminium alloys containing both lithium and beryllium, two different precipitates form independently [1]. The A13 Li (f') phase precipitates.as fine, coherent spheroids which will provide a significant contribution to strength [5,6].…”

Microstructural evaluation of arc-melted Al-Li-Be alloys

“…The potential for weight savings in such structures is significantly higher for A1-Li-Be alloys than for any other aluminium alloy system, including metal-matrix composites. In a preliminary study of A1-Li-Be alloys [6] using the S-3A Naval Patrol Aircraft as a structural example [4,7], the weight savings were calculated for two illustrative AI-Li-Be compositions: A1-3Li-3Be and A1-3Li-10Be. The results, together with similar calculations (made using experimental data [8][9][10]) for other advanced aluminium alloys, as well as for a metal-matrix composite [11], have clearly demonstrated the important potential benefits of the A1-Li-Be alloys.…”