In aeronautics industry, airframes are primarily made of riveted Al-alloy panels, with a skin and stringer configuration. The requirement for reducing manufacturing and operational costs has lead aerospace industries to look for new, attractive ways to substitute conventional riveting techniques in airframes. Towards this direction, advanced welding technologies such as friction stir and laser beam welding are a promising solution. Innovative aluminum alloy 2198 is a relatively new alloy compromising low density, high modulus of elasticity and good damage tolerance and has been already used for aerospace applications. The mechanical properties of these alloys are quite often associated with the Li concentration that enables the formation of several strengthening precipitates. The tensile mechanical behavior of both reference and laser beam welded aluminum alloy 2198-T3specimens will be examined in the present work. Sheets of 3.2 mm thickness were laser beam butt welded and two different filler wires were examined, namely AA4047 and AA2319 having 1.2mm and 1.0 mm diameter, respectively. The tensile specimens were machined from the welded sheets from the longitudinal (L) rolling direction of the sheets, according to ASTM standards. The specimens were post weld heat treated (PWHT) at 170oC and for different ageing times so as to bring the material in all possible ageing conditions, namely under-ageing (UA), peak-ageing (PA)and over-ageing (OA).The experimental results showed that when using filler wire AA4047 more sound joints were produced with the absence of structural faults. This was not the case for AA2319 where hot cracking and porosity was observed in a considerable way. It was observed that the angle of the filler wire feeder has a significant role of the surface and the distribution of the filler material during welding. As expected, filler AA4047 is less sensitive that AA2319 to the ageing conditions due to low precipitation fraction that has a profound effect on the evaluated tensile mechanical properties. Microstructure evaluation, hardness measurements along with the essential trade-off between tensile strength over tensile ductility for the investigated ageing conditions are discussed in this thesis.
University of the Aegena
