AbstractThe present paper concerns the microstructure of electron beam (EB) butt welded 2219 aluminium alloy. Crack and porosity free joints were obtained. The EB was also used to carry out in situ post-weld treatments. As a consequence, the microhardness was raised significantly to values very similar to that of the untreated alloy after five pass EB treatments. The contribution to the enhanced microhardness is thought to be related to the early precipitated CuAl2phase and immobile dislocations. The microstructure is discussed in terms of effects induced specifically by EB processing. This investigation shows that the in situ post-weld treatments can be regarded as a useful procedure for improving both microstructure and properties of EB welded joints.MST/3084