Effect of the Number of Welding Repairs with GTAW on the Mechanical Behavior of AA7020 Aluminum Alloy Welded Joints

In this work, two different tests were done to establish the effect of heating cycles by welding in an AA7020-T6 aluminum alloy welded with ER5087 and ER5356 electrodes. During 10 months, welds were done to simulate in the laboratory several welding repairs (up to six repairs). Tensile and hardness measurements were done to evaluate the evolution of the properties against time. It was found that a single pass is enough to generate a heat-affected zone (HAZ) of 30 mm, and after four repairs the width of the HAZ exceeds 210 mm. In the HAZ, two regions were observed: the dissolution zone, which recovers a percentage of hardness by natural aging, and the over-aging zone, showing no increase in hardness. The results indicate that there is a maximum number of welding repairs that can be performed in a heat-treatable aluminum superstructure before it fails on the HAZ of the base material, since the tensile strength is reduced around 40 pct compared to the base metal.