Abstract
The characteristics of the fatigue crack growth in the base metal, weld metal and heat affected zone (HAZ) were quantified by testing compact type specimens of 6061-T6 welds obtained by the modified indirect electric arc technique. The fatigue crack growth depends on the microstructure imposed by the welding thermal cycle and it was observed that in the HAZ the crack growth rate is lower than that in the weld metal, but higher than that in the base metal. Microhardness maps revealed that this behaviour is due to the formation of a larger plastic zone around of the crack tip produced by loss of hardening. A comparison of fatigue crack growth of weld metal and HAZ for modified indirect electric arc and friction stir welding shows that the weld metal produced by friction stir welding exhibits better resistance to crack propagation, but both processes behaved similarly in the HAZ.