Welding Tips and Tricks

OK here goes. The material in question is 6061 T-6 aluminum tubing. It has had a propane torch flame applied to the inside end of it to soften some industrial grade epoxy structure adhesive. The adhesive has a glass transition temperature of 68 deg C. or about 155 deg F. This is the point that the adhesive starts to get soft. I know that the T-6 ages at or near 250 deg F. Anything hotter than this starts the temper down hill from there. I know that the flame from the propane is a around 1000 deg F. The tube was said to be heated enough to soften the adhesive and no more. I feel sure my helper meant well but I think there has been a weakening of the metal. After welding it is temper “O” right next to the weld. 18 KSI or near it....down from the 45KSI in full T-6 temper correct so far? But a propane torch is far from a weld pool temperature. Or does it need to be looked at like a TIG machine with too low heat to make a puddle....Bad. I have read some peoples theory that it will naturally age harden to near T-4 in a few days but I can’t find any documents to justify this with less than a 250 deg interpass temp. The lowdown of this is it will be easier for an elephant to ride a Harley than to replace it. So what do you guys think on this? I really don’t know exactly how hot the tubing got...but I am sure it was done a lot faster than a weld would take to do. Is it scrap? It can’t be re-heat treated....has other components on/inside it....carbon fiber parts.

Hey,

Too late now, but should have used boiling water to soften the glue.

Mick

weldin mike 27 wrote:Hey,
Too late now, but should have used boiling water to soften the glue.
Mick

+1 for boiling water

My knowledge of aluminum metallurgy is relatively weak and my references for it are in storage, BUT,

If the epoxy didn't smolder, or carbonize anywhere during this "cooking", you probably did not exceed a critical temperature. Generally, thermosetting plastics will begin to break down and carbonize around 450F, and the flame will bring the plastic to that temp before the metal reaches it (as the epoxy conducts heat away poorly, and aluminum quite efficiently).

My opinion is, if you're not cleaning lamp-black and burnt glue off the material, no harm was done.

Steve S

Thanks for the info...been chasing info all day. And tested some same materials...I learned things today. Dug my torch and IR temp gun out and wanted to see what could be found with what I have on hand....no hardness testing. I set a piece of the same tubing on the table and heated it as if I were trying to get the glue to soften....and made a test part with glue and all. It released at 233 deg F. The old sharpy annealing test showed a 268 deg F when it went away. Didn't check it with the O/A torch by sooting and burning that off. Closing off the end of the tube increased the temperature by 5-6%. The absolute highest temp I could get with the torch was 338 deg F indicated. I took some smaller strips about 1" wide and could melt them ! It would measure way over 370 when it would plop off the end of it- it got hot fast and I am not sure if it was getting the hottest part of the strip. I could not get the tube to melt at all. I tried to leave the torch propped up on it and just left it for a couple minutes....nothing.
I think that the tube dissipated more heat than I thought. The heat seemed to move evenly and dropped quickly as it spread from the heated area. Even at 8 inches away it was very hot to the touch , but measured less than 160 deg F. I checked the temp gun with ice, the thermometer in the freezer and fridge, pot of boiling water{bubbles @ 186 deg F} and just for kicks and giggles torched a small piece of 4130 to see the blue colors and try and match those with readings and blacksmith's charts. Seemed very close.
The tube that was tested met with my linesman pliers. The heated area on the end was easy to peel around and tear it off. Assumed fully annealed there for sure. About 8 inches inward it started to feel more solid and resisted tearing away. This was confirmed by sampling an unheated tube in the same manor. I tore that whole tube up on chunk at a time with the pliers just to see where it was not soft.
Sorry to be so long winded...just wanted to share what I had learned today with backyard experiments. So it seems the area that is/was most affected is right where the heat was put in. Guess I need to get a Vickers type tester out here to know for sure. That unit makes a diamond impression in the test metal and is compared to known charts for that material. This has gotten a lot deeper than I thought it could go....another learning curve with hardest lessons least forgot ....
Would pay to see what the AWS D1.2/D1.2M:2008 has to say about this......just can't afford the whole book!