The aging characteristics of rapidly solidified high lithium AlLiMg alloys

AlLiMg alloys containing 3.1-3.9wt.% (10.8-13.6 at.%) Li and 1.0-7.4 wt.% (1.0-7.5 at.%) Mg were rapidly solidified by chill-block melt spinning to produce ribbons typically 35 μm in thickness. An initial hardness of 66-178 kgf mm^-2 increased to 160-240 kgf mm^-2 on heat treatment at 160 or 190 °C. Studies by X-ray diffraction and transmission electron microscopy showed that formation of equilibrium δ (A1Li) phase had been suppressed in all the alloys by melt spinning but that δ′ (Al₃Li) phase had precipitated at high volume fraction and on a fine scale in the α-Al matrix, as spun. Heat treatment of alloys containing less than 4 wt.% Mg resulted in coarsening of this δ′ phase and precipitation of δ phase. For alloys containing more than 4 wt.% Mg, coarsening of δ′ was followed by some replacement of this phase by the equilibrium Al₂MgLi when heat treated at 190°C. The ternary phase precipitated in a homogeneous distribution of particles, about 300 nm in size, which maintained the hardness of the alloys. Prolonged heat treatment caused complete dissolution of the δ′ particles. The significance of these results for the development of high Li, high Mg aluminium alloys with attractive mechanical properties and a low density is discussed.