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fillet welds aluminum vs steel leg length

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  • fillet welds aluminum vs steel leg length

    i’m just doing some structural work on some aluminum yachts. just wondering if we follow the same formulas to find weld size (throat, leg) as steel as we have no drawings
    Last edited by megswesterman; 01-11-2018, 01:37 PM.

  • #2
    The formulas for carbon steel fillet weld strength do not apply to aluminum fillet welds,
    because the HAZ is annealed as a result of the welding process as is the weld filler material.
    Last edited by Almond farmer; 01-14-2018, 11:01 PM.


    • #3
      During my time building anodized structures for boats I was a bit shocked to learn none of the pipe joints are notched, the pipes are balogna cut and the gap filled the prettied up once the joint is connected.
      I have never subscribed to this technique so needless to say when proper fabrication (structural integrity) practices are secondary to speed and charging too much for marginal workmanship I left the boat industry, I refuse to do improper fabrication despite the fact it seems to be industry wide.
      To answer your question, my rule of thumb for aluminium is a puddle approximately 1.5 to 2 times the wall thickness depending on the pipe size, the smaller width on say 2 inch and to the wider on 2 inch plus, on 3 inch or larger don't be afraid to add a bit to bead/puddle size, most times you want to strive for a flat bead profile.
      I hope this helps.
      Last edited by Vintage Racer; 01-18-2018, 04:58 PM.


      • #4
        I generally prefer to bevel parts and then also try to make sure there is some "crowning" to prevent the weld from breaking. A bit wider than equivalent steel welds would be acceptable for me also.
        Good fit-up is key on anything welded IMO.
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        • #5
          Aluminum is different than steel for a number of reasons. Proper heat is as critical of not more so than leg length. You need the heat for penetration, as well as allowing for hydrogen to escape before the puddle cools. If your weld is too cold, or if the material needs a preheat when the heat from the arc isn't sufficient...the puddle cools faster and your weld will have more porosity, despite looking perfect on the outside. Thats more for thicker material. A pulse mig will also help you if you can't tig it. Slightly wider leg than steel though.


          • #6
            Lincoln electric has an article in the online learning center on strength of aluminum structural welding.
            Oregon has an aluminum boat industry within the state and most of the AL in the area is supplied by Pacific Metals in Portland.
            5052-0 & 5052-H32 are the preferred AL alloy for small Aluminum boats unless you are the Navy that uses, 5086,5086-H116, 5086-H32.

            ​​​​​5052-0 yield strength equals only 13 KSI, while 5052-H32 yield strength equals 28 KSI.
            The HAZ is about 3/4" long from the fusion line. The 5052-H32 Material in the HAZ , looses ~ 80% of the strain hardening strength.
            so the H32 alloy is reduced in strength to ~ 19 KSI, about the same as the less expensive 5052-0.
            The actual AL filler metal also has about the same strength , if using .045" , 5356 filler wire

            boat hulls have to endure a whole bunch of pounding loads.
            took my 30 ft , dual screw search from the Columbia river to the Willemette river junction , a fast moving large boat crossed my path and created a wake, my boat totally came out of the water, air between bottom of hull and water surface, slammed back into the river and all the glass windows retained by rubber molding popped out of the hull. DORRY style boats are very popular in the northwest because the aluminum absorbs the impact from the river rocks , while fiberglass will shatter.