Evaluation of properties and microstructure of non-heat treatable Al-Mg-Li-C-Oalloyswith variable Li concentration

Fine grained AI-Mg-Li-C alloys, with lithium concentrations from 0.7 to 1.5 wt-%, have been produced by a mechanical alloying-powder metallurgy route. An initial range of compositions was chosen for manufacture into 10 kg bil lets which were uniaxially forged into plate; subsequently two compositions , alloy A (Al-3.7Mg-0.7Li-1.0C (wt-%)) and alloy B (Al-4.4Mg-1.4Li-1.0C), w ere down-selected for a 20 kg scale-up exercise. Billets were forged at 300 degreesC, using an 8:1 reduction ratio, which provided a sufficient level of work to develop properties, while avoiding excessive grain growth. Ahoy B exhibited tensile properties (0.2% proof stress 450 MPa; ultimate tensile strength 510 MPa; strain to failure 6%) that exceeded the AECMA specificat ion for AA 5091, Both alloys were confirmed as non-heat treatable and there fore exploitable in the as forged T1 condition. Microstructural analysis ha s confirmed that a fine grain size (<1 pm) and nanoscale Al2O3/Al4C3 and Mg O dispersoids provided significant Hall-Fetch and Orowan strengthening, res pectively, capable of increasing the 0.2% proof stress to 450 MPa, Although optimisation of thermomechanical practice is still required, these Al-Mg-L i-C alloys show considerable potential for aerospace, land, and space appli cations. MST/4728.