6063 is a bit more formable than 6082 for any given temper although probably very little in it when annealed. What CLR and DOB are we talking about? What's your annealing procedure?
Aha thanks Richard. Ive formed bends up to 90 deg and 2xCLR.Degree of bend. Centre line radius.
To know How it is failing would help. It can fail because of two two reasons (assuming there is no material problems) 1 under annealing and 2 over annealing. From what you have said and the colour you are taking the soap to, you are under annealing and and leaving the material too hard this normally fails with of bit of a bang and its an instant fail rather than a progressive one. I suggest you do some practice runs on getting the annealing process correct. If you are using a soap you need to take the soap to black which is a very fine line from the brown and can easily be confused as you will get black tinges in the brown. as soon as it black remove the heat otherwise you will over anneal. A better method is always preferred as mentioned like heat soaking in a controlled conditions ie an oven or some better method to detect the temp, but of course those our out of the reach of most people.
You must also keep in mind its a tube, you can not simply apply the heat to one side having a soap line on the other. Put several soap lines down the piece a minim of 3, you can then see what is actually happening with the material with one you can not. The heat soaks through therefore you will will have one side hotter than the other, you need to rotate the tube and play the flame up and down the area you want annealed the to give even coverage and proper heat soak. If this is not done correctly you will end up with hard areas and softer areas and the result of that is self explanatory.
The fact you are doing 1.6 isn't really helping as the heat increase will be rapid, something that soaks the heat more, is more controllable for manual annealing. Also my personal feeling is Oxy ace is a bit fierce and very concentrated and makes it harder to give an even heat. I have always used propane with an adjustable regulator because it gives more coverage is a softer flame which means the heat input is far more controllable. It's a controlled soak you are after not a big concentrated heat input. This one i think is about technique and practice.
There are more formable flavours of tube but you'll struggle to get them (or 6063 / 6082 in any temper other than T6) without paying for a min production run and/or they'll be available in a very limited range of sizes for example https://www.aircraftmaterials.com/data/aluminium/5083.html
Personally i've always hated soap as a crude/cheap temp indicator. With oxy acetylene i'd soot the area up instead and then bring in the O2 to heat the thing up until the soot burns off. As said it's fairly easy to overheat stuff or even melt it if not paying enough attention. Dark coloured permanent markers work in the same way as soot so with propane etc can colour in the area to be annealed and heat until the ink burns off. Works best if you 'chase' the ink i.e. don't heat it directly, start next to the coloured in area and chase it as the ink starts to disappear while rotating the tube. If you've got some channel kicking about can weld/clamp a couple of sheet metal 'v-blocks' into it to make life easier and help reflect the heat around the tube
Or, as said, a tempilstik makes for a more accurate temp guide. Annealing temp for the 6xxx series is 412°C and to truely anneal from T6 they need soaking for ~ 3 hours and controlled cooling according to the books although simply taking them upto temp and letting them cool naturally softens 'em lots and should be enough providing the tube isn't put aside for a day or 2 before bending
Does it collapse before failing or just break? Under annealing makes more sense at the min but mandrel position could be playing a role