RECYCLING OF ALUMINIUM-LITHIUM PROCESS SCRAP

The yield of finished aluminium-lithium product from suppliers' semi-fabrication facilities varies with the product form but is generally quite low. The yield of finished aircraft parts in the aircraft manufacturers' fabrication processes is even lower. Of their scrap, some is heavy, relatively easily segregated and might be taken back by semi-fabrication plants for direct recycling. However, the bulk is in the form of machining swarf which will be unsuitable for direct recycling due to mixing with other aluminium alloys and other aircraft materials such as stainless steel and titanium. For conventional 2XXX and 7XXX aircraft alloys, swarf is sold off to scrap dealers and secondary aluminium smelters for conversion to aluminium-silicon foundry alloys. The paper seeks to quantify the material flows for the industry as a whole, identify the problem areas and indicate a range of potential short and medium term solutions requiring R & D. In particular, results will be presented on mechanical property measurements on laboratory cast samples of two aluminium-silicon alloys containing up to 8000 ppm of lithium. While modification of the microstructure occurred in the region 200-400 ppm, no significant effects on UTS were observed. Further work on a wider range of alloys and properties (including electrochemical properties) is planned.