Localised T (tau) phase precipitation at the weld toe of gas metal arc welds was correlated to stress corrosion cracking in the lap joints of aluminium alloy 7003 (Al-Zn-Mg) welded with AA 5356 (Al-Mg) type filler wire. To further investigate the detrimental effect of T phase precipitates on cracking initiation, two strategies were developed. First, welds were made with AA 4043 (AlSi), eliminating the T phase precipitation, while maintaining similar heat affected zone characteristics. Second, the toe region of Al-Zn-Mg weld, made with AA 5356 filler wire, was post-weld friction stir processed through which the T precipitates were displaced and encapsulated in a subsurface region, isolating those precipitates from the surface corrosive environment. For both cases, an increase in cracking resistance was demonstrated. The impact of processing on joint strength was discussed based on the lap shear tensile testing data.

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