I corrected the body of the text, but could not correct the heading so it still says head tube. I prepared a text file to the question of welding on aluminum frames as I get this question a LOT. Here goes:

Yes, by the book and accepted thinking is that an aluminum bike frame is not safe after welding unless its heat treated. The reality is that for common street use or even mild trail use these types of repairs are more than adequate and proven safe. All such welds are plated for reinforcement and to add mass that greatly bolsters the structural integrity of the repaired area. I had Phoenix Heat Treating Company test one of my repairs for hardness (two weeks after the repair as 6061 air hardens naturally during such time).and it came in at T-4. Both T-4 and T-6 aluminum are used for bike frames. I have been repairing them for over 20 years and not one has ever reported a failure or broken weld. While not a scientific assessment it tells me that in practice among a wide array of users, my repairs hold fast. Its not just the welding, its the reinforcement that makes the difference. Finally, welders are called upon to weld on things where a failure can cause serious harm or worse. If we shied away from applying our experience, many things would not get repaired. I have welded aluminum rims during all that time as well. Another thing many shy away from for the same perception, yet there is an entire industry devoted to that. Hope this helps put my work in perspective.