The influence of small voids on the fatigue strength of friction stir welds in the aluminium alloy AA6061-T6

S. Kahl
Sapa Technology, Finspong, Sweden

Flat rectangular profiles of the aluminium alloy AA6061-T6 were friction stir welded to butt joints. Welding parameters outside the process window generated a random mixture of good welds and welds with small voids. These voids approximately reduced the tensile strength by 10%, the ductility by half, and the fatigue strength by 20% as compared to void-free welds. Voids can easily be detected on fracture surfaces. Void-free specimens have approximately 10% lower fatigue strength if the fatigue crack extends over a corner of the specimen cross section as compared to a semi-elliptical fatigue crack.

Key words: Fatigue testing, friction stir welding, aluminium alloy