Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications Part I: Local gradients in microstructure, hardness and strength

Sheets of AA6056 and Ti6Al4V were butt‐joined by inserting the Ti‐sheet into the profiled Al‐sheet and by melting the Al‐alloy alone using a split beam Nd:YAG laser. To study microstructural effects on properties, the Al‐alloy was used in two tempers; T4 followed by post weld heat treatment T6, and in T6 followed by a defined duration of natural ageing at room temperature. As a basic step for fatigue and fracture investigations, local gradients in properties of this dissimilar joint are investigated using microscopy, hardness and tensile tests. Possible sites, from which fracture may initiate, have been then identified. All property changes are found to confine to the aluminium side. An intermetallic layer, although very thin, is found to form on the interface. The changeovers, firstly between the fusion zone and the heat affected zone and secondly between the heat affected zone and the base material, are found to be associated with changes in microstructure, hardness and strength. These are identified as the possible critical sites in addition to the interface.