Not entirely true, hence my comment about the welder staying on it too long. Changes on strength depend on heat, time and amount of weld depsosited, which contributes to your heat affected zone, not to mention the type of force being applied under working load. Not sure how you were able to come up with the calculations to indicate a 70% weakening. Alluminum can actually be heat treated without needing to be annealed, especially for this aplication. Good luck.