I appreciate the concern. Yes, 6061 does loose its temper when welded. I am planning on doing some artificial aging to help return some of the strength. I am aware that this is less than ideal, however, I am not terribly worried because the early aluminum swing-arms from Suzuki were not heat treated post weld (this is off a '82 GS1100). Furthermore, Its fairly common practice to lengthen aluminum swing-arms and no one heat treats. The guy that did the welding has done loads of aluminum swing-arm mods over the years and has never had an issue. Once I start riding the bike I will be scrutinizing the welds for cracks. If any cracks appear I will probably build a new swing-arm from scratch so I can use the appropriate filler rod so it can be heat treated. In retrospect I should have done that in the first place, as it wouldn't have cost me much more money but it would have been substantially more time.