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Aluminum brazing vs. welding

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  • #16
    Ive done some aluminum brazing with a rod called alladin 3 in 1,worked real good cleaned with a ss brush dida little preheat and it flowed right in,was a hole patch on an aluminum row boat they also use this rod for rebuilding boat props

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    • #17
      Originally posted by Laiky
      I disagree on brazing causing less warpage of stainless. The total heat input is larger and over a larger area. The TIG arc although 4 times as hot is in a much smaller area and the total heat input should be less. You also get the option of a pulser with TIG

      I gotta agree with you Laiky, the heat is much more focused with the tig welder as compared to o/a brazing. I would think that you would get a ton of warpage with brazing....esp s.s.

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      • #18
        Originally posted by Luna
        Less heat = less expansion
        Less heat ? maybe lower temp but bigger h.a.z.

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        • #19
          HAZ means you have gone past a temperature of which the basemetals crystaline structure has changed due to the heat input. Al wickes heat away so fast that the issue becomes that of how long are you putting heat into the piece.

          Since these Al brazing rods only require a hair shy of 800*F a very hot o/a is the best choice since you can really move fast. With tig, well, it takes a while. Mig of course is pretty fast. I've never timed it but since I can weld Al with O/A quite a bit faster than with TIG, I think the brazin operation should be just as fast. So just compare the two simplistically time_of_heat_input x temperature per inch. (This still ignores the all important extra amount of energy used in TIG for the phase change, so TIG is being given a helping hand here)

          800xTorchTimInSec/per_inch vs 1200xTIGTimeInSec/per_inch

          Lets assume 1 inch (I'm doning this quickly so please excuse a lapse of reason or accuracy )

          So if O/A braze is 2x TIG speed=(800*.5)/1200 =30% of the TIG heat input
          So if O/A braze is 1.5x TIG speed=(800*.75)/1200 =50% of the TIG heat input
          So if O/A braze is 1x TIG speed=(800*1)/1200 =66% of the TIG heat input
          So if O/A braze is .5x TIG speed=(800*1.5)/1200 =100%/same as TIG heat input

          So it ultimately comes down to speed in regard to HAZ. However haz isn't the cause of warpage though. Snce the discussion is really about Al, warpage isn't much of an issue anyways.

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          • #20
            I was referring to stainless. But i think it still holds true with alluminum
            Dynasty 200 DX
            Millermatic 175
            Spectrum 375
            All kinds of Smith OA gear

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            • #21
              Jeff,

              I have done lots of AL welding. Mig, Tig, gas and also a fair amount of AL brazing. The answer to your question is that everything else being equal, welding will always be stronger than brazing.

              Now, the question is, when is everything equal. A proper AL weld is more difficult (no matter the process) than a AL braze. So is a proper AL braze stronger than a poor AL weld? Very possibly.

              I do lots of AL brazing of thin AL sheet and in many cases, welding would not even possible because of the necessity of not melting the base metal and brazing is strong enough. But brazing large 1/4" AL plates would not be practical or in most cases, not strong enough for the application.

              But if you still find muggy weld fits all your needs, I'll be glad to pay the shipping charges for your welder.

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              • #22
                Brazing Aluminum

                All,

                Another very important consideration for brazing vs. welding is fatigue strength . When most talk about strength, they are talking ultimate or yield strength . Fatigue strength is just as important in many applications . Brazing metals relies on lots of surface area adhesion to create the strength . But this is a surface effect and more highly stressed by fatigue loads . Don't get caught up in the "strength" contests of a welding process without asking all the questions .

                I remember using the "Alumiweld" rod for brazing some thin tubing . It was quite strong but failed quickly due to very little fatigue strength . Making a larger fillet, help slightly but you couldn't put enough rod on to get any real long-term strength .

                Brazing has its place, IMO, for less loaded or non-critical joints (and never for but joints) . Welding does cause the parent material to become weaker, but the fatigue strength may actually improve to the gain in ductility .


                >>Tim

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