View Full Version : aluminum welding TIG vrs A/O torch HAZ questions
Here is an interesting question I hope someone can answer
OK since the TIG's HAZ is so small and sharp(as you move perpendicular away from bead the temp drops exponetially in short distance) wouldnt that mean that the boarder of the HAZ would be weakend by the expansion and cooling compared to the metal adjacent to it which recieved no heat.. couldnt the metal theroetically 'pull' away internally and possibly crack due to this.
I would figure that the larger HAZ of a O/A setup would provide more suitible conditions. basically opposite of above.
I just think the extreme temp differences over a small distance from TIG welding would make for some interesting stresses.
opinion/flames/facts desperately wanted.
btw i started thinking about this after I read a book by carol smith(engineer to win)...although I coulda misread it...I was reading in car and kinda dosed off a couple of times
01-26-2004, 10:17 AM
Have you ever tried to weld alum. using torch or tig. Torch welding I did 25 years ago and only because I was in school, I would think you will do much better with tig. Torch on alum. is quite tricky.
yea I went back and glanced at the book. It was Chrom-moly 4340 he was talking about. something about forming masonite at the boarder of the HAZ. I havent taken metalurgy yet and was wondering if this is true on all metals welded with TIG.
also I would figure a GOOD pre-heat and post-heat will ellimante all the problems on most metals.
Im not really looking to do any al welding if I can help it since my TIG is a HF(yea yea) DC inverter with a torch on it....
any al I would have to have weldedd I'd prolly do it with my powermig200 any ways
01-26-2004, 12:35 PM
Not sure how helpful this is, but a site called tinmantech.com is run by an old school guy who thinks oxy-fuel is the only way to go, even with aluminum. I had some questions once, called their shop and ended up speaking to the owner. He was really helpful. He sells flux for such things as well (something I've never seen for Aluminum in my local welding shops). I tried it once on some scrap and it wasn't too bad. Not sure about the weld strength though. I didn't notice any cracking.
01-26-2004, 01:25 PM
We talked about this a few days ago in another posting. You are right about the narrow HAZ, especially on 4130. What may form along the edges of the HAZ is untempered martensite.
Martensite is the hardest austenite decomposition product and results from excessive cooling rates (i.e., no preheat or postheat), where the surrounding steel acts as a heat sink. High carbon martensite is hard and strong, but also brittle and can create problems in the HAZ. The higher the carbon content of the steel, the worse the problem.
Martensite alone will not cause cracking, dissolved hydrogen and residual stresses are also necessary. The hardness of the HAZ is usually a good indication of the cracking tendancy. If the Brinnell hardness is below 250HB, you usually won't have a problem. But if it approaches 450HB and no tempering has been done, you may be in the world of hurt. Comparing the base metal hardness with the weld hardness should be useful to predict cracking tendancies.
With O/A welding, the HAZ is much broader, some preheat is a given and postheat is easy. It's a lot more foolproof. All of this is why I am reluctant to strap my posterior into an air'chine with a 4130 tubing fuselage that has been tig welded and go beat up the sky.
01-26-2004, 03:19 PM
Here is a link to answer your questions on 4130
I saw the previous post after I got home from class. But thanks for the info guys.
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