Weldability of Li-bearing aluminium alloys

Lithium bearing aluminium alloys constitute a. relatively new generation of high performance, lightweight aviation alloys that are being considered fo r a variety of applications requiring welded construction. As with other al uminium alloys, there are a number of weldability issues associated with th ese alloys, including resistance to defect formation during fabrication, me chanical property degradation, and service performance. This report reviews the pertinent literature regarding the welding characteristics, properties , and weldability of a number of commercial alloys. The review is divided i nto the following major sections: (1) development and physical metallurgy o f AI-LI-X alloys, (2) microstructure evolution, (3) mechanical properties, (4) weld cracking susceptibility, (5) porosity formation and prevention, an d (6) corrosion behaviour. The commercial AI-LI-X alloys are welded using a variety of processes, including are welding, high energy density welding, and solid state welding. The strength of welds in these alloys varies widel y, depending on the welding process, filler metal selection, and post-weld heat treatment. In general, these alloys have low joint efficiency (ratio o f weld strength to base metal strength) in the as welded condition and requ ire post-weld aging to achieve efficiencies substantially above 50%. Weld p orosity has been a particular problem with these alloys in part due to the hygroscopic nature of Li-containing aluminium oxides. This problem can be c ontrolled if proper surface preparation and cleaning procedures are used. T he AI-Li-X alloys tend to be more susceptible to weld solidification cracki ng than comparable alloys without Li additions. Basic weld solidification t heory is used to explain this increase in susceptibility. Some of these all oys exhibit an unusual fusion boundary cracking phenomenon that is associat ed with an equiaxed grain zone that forms via a solidification mechanism in alloys containing Li and Zr.