Hello schulerg, I would say the short answer is that it is possible. Unfortunately I believe the long answer is that it isn't very probable. A number of things come to mind here, you have a very thin ring that has very little heat absorption ability when compared to the thicker part that you may be joining it to. That being the case it will be very difficult to bring both parts to the same energy level at the same time to perform an autogenous weld. Depending upon it's use it may also exhibit an excessive amount of undercut at the toes of the weld bead, how much will this affect it's purpose? How will you position and hold this ring while the welding is being performed? The coefficient of expansion of aluminum tends to make it crawl all over the place so keeping it round and tightly contacted to the other part might be difficult. If you are planning on tack welding it before making the weld I believe that will also interfere with your plans to perform the welding. Using a backing fixture made of stainless steel might help with issues of equal heat distribution, yet you would probably need to invest considerable time getting this figured out. Your material would also need to be spotlessly clean and oxide free, otherwise you wouldn't be able to readily get it to fuse. A little better description of the parts and their relationships to one another might allow for a better response from everyone. You are proposing a tough one here. Best regards, aevald