Welding should't weaken any material if done properly, but the material Has to have some sort of a defect to crack. Welding on defective material will only introduce stresses into another part of the defective material. The material must not have been heat treated in the proper manner

 

My riding buddy owns a aluminum fab and weld shop and tells me he has repaired several aluminum swing arms from bikes, none have come back, welding should only be done by a experienced welder with a TIG to get excellent penetration, may want to add some reinforcment. With a aluminum unit I would give it a close inspection before each ride, personaly for a DS I like chromo, just another .02

 

Hey guys thanks for the input. I will see if he is going to replace the swing arm today. I will let everyone know what kind of customer service this shop is offering after getting the money. I hope I have only good things to say later in the day.