Strength and Fatigue Resistance of Laser-MIG Hybrid Butt Welds of an Airframe Aluminium Alloy AA6013

Abstract

Hybrid welding is, as regards selection of welding parameters, a tolerant process. On the other hand, the weld seam and the heat affected zone may tend to be wider as in an arc process, which may be detrimental to mechanical stability. With CO 2 laser beam buttwelds as a basis for comparison, properties of butt-welds of a peak-aged airframe alloy AA6013-T6/3.2 mm, produced by Nd:YAG-MIG hybrid, are investigated. A filler wire (AA4047; AlSi12) was used for both types of welding. It is found that the hybrid process coarsened the microstructure in the fusion zone partly. Furthermore, although the weld seam and the heat affected zone were wider, mechanical properties were not at all adversely affected. Changes in hardness and tensile strength were marginal and the fatigue performance was in fact improved for the hybrid welds. These results are presented and discussed. It is concluded that the hybrid welding deserves consideration for fatigue critical applications.

Structure‐property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications. Part II: Resistance to fatigue crack propagation and fracture

“…Resistance to fatigue crack propagation in the underaged condition (T4; GP zones) is found to be better than that in the peakaged condition (T6; " precipitates), both for the base material and the laser beam welded butt-joints of AA6056 [21][22]. Moreover, overageing ( " '/Q' precipitates) in the heat affected zone of a comparable alloy has been found to provide a fatigue crack propagation behaviour as good as to that in the base material [23]. Thus, a type of precipitates that improves strength and hardness (e.g., ") may not necessarily improve the fatigue crack propagation behaviour.…”

“…Thus, as regards the resistance to fatigue crack propagation, underageing or overageing turns out to be more beneficial than peakageing [21][22][23]. It also needs to be mentioned that at the interface stable fatigue crack propagation was observed (and not uncontrolled separation or debonding) and when welded in T6, the fatigue crack propagation response was as good as that of AA6056.…”

“…Nonetheless, some microstructural influence depending on the ageing has been found in 6XXX Al-alloys [21][22][23]. Resistance to fatigue crack propagation in the underaged condition (T4; GP zones) is found to be better than that in the peakaged condition (T6; " precipitates), both for the base material and the laser beam welded butt-joints of AA6056 [21][22].…”

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

“…Grain boundary liquation is typical [29][30][31][32][33] to butt joints of laser beam welded 6XXX Alalloys that are welded by the keyhole mode. In the present case energy input was not that high due to the heat conduction mode.…”

“…Towards the end of the fusion zone a transition zone was formed where the elongated grain started to appear and their form tended to become comparable to that of the base material. At the end of the fusion zone and the beginning of the heat affected zone grain boundary liquation was observed up to a length of about 4 grains.Grain boundary liquation is typical [29][30][31][32][33] to butt joints of laser beam welded 6XXX Alalloys that are welded by the keyhole mode. In the present case energy input was not that high due to the heat conduction mode.…”