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Machining aluminum welds

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  • Machining aluminum welds

    I've got a model engine block project made out of 6061-T6 that I have a fair amount of time invested in that I decided to attack with a bandsaw without thinking about where the bellhousing was going to mount to... as a result, I've got a piece of aluminum (somewhat small, 1/4" x 1/2" or so on a 6"x4" block) that was going to serve as my bellhousing mount not connected so well to the block at the moment. I have a TIG welder and know how to use it, but I have never had a lot of luck machining aluminum welds... material is gummy and finish is not so good. As luck has it, this is going to end up on the outside of the finished model, so obviously I'd like to get it to blend as well as I can. I have heard of methods to try and regain the heat treated properties of aluminum in welded zones, but I guess I was just hoping someone on here would have some first hand knowledge pro or con of trying to just heat the block up in an oven and hoping for the best. This isn't the last operation on the block or even close to it, so I'd just as soon not ruin the whole thing for the rest of the machining. I can wait until I am close to finished to try to fix it, but I'm sure you guys can sympathize with me in looking at the saw cut and wanting it fixed right now I guess I am just feeling sorry for myself a little bit and trying to find a solution at the same time, so if anyone has any ideas for me, I sure would be grateful. Thank you.


  • #2
    I had one large diameter piece which needed a hub welded on. I didn't have any problem machining it. I'll admit to not welding it myself---I am fine with steel, but no experience whatsoever with AL. If you can , bevel the joining edges between the two pieces. I asked my welder to build up a bead and I machined it back. Turns out it is pretty tricky to not see the line at all. It can look real smooth and uniform, but the line is likely to be discernible. I'm sorry to have to tell you that. If you have trouble with the "gumminess" I recommend brushing on a little Tap-Magic Aluminum or other cutting fluid while doing the cut. It helps immensely.


    • #3
      I have had to do this many times in my career. I know what you're talking about when you say gummy and I can just picture the machined finish ... been there many times. I am not aware of any heat treating procedures to regain the original machining properties. I am far from an expert on the fine points of metallurgy but I suspect that the intense heat boils off some of the added alloys or causes them to recombine in some abstract way which might preclude any heat treating solutions.

      I've always just taken my time when machining an aluminum weld for looks using plenty of cutting oil (oil vs kerosene) and a very slow feed and light cuts when approaching the end leaving just the slightest bit of material on the surface. Then, just the usual elbow grease with files, descending grades of emery and finally some Scotchbrite. It may be necessary to re-weld any pits left after finishing and repeating the process locally on the new welds, but if you are careful and patient you'd be surprised at how nice you can make it turn out especially if you have the luxury of being able to sandblast it at the very end. Good luck and I'll be checking back to see if anyone else has any better solutions ... I would sure appreciate hearing them.
      Last edited by DATo; 12-22-2011, 05:15 AM.


      • #4
        I'm sure someone with more experience will chime in, but I don't think 6061 T6 is weldable. I vaguely remember that is has to do with the heat treating.



        • #5
          Read this.

          Stu, 6000 series aluminum is very weldable. 2000 and 7000 series NO.

          Hope this helps.
          JIM : You don't get a 2nd chance to make a 1st impression.


          • #6
            Put enough bead to build up the surface you need, and then hammer the bead and flatten it out. This work hardens the metal and will give you back some better machining characteristics.


            • #7
              I have never run into your problem machining aluminum welds or the surrounding area of the weld. I TIG all my welds and use either 4043 or 5356 rod, even with the 4043 being the softer of the two it still machines like the surrounding area does, the only thing that might be noticable is a slight discoloration in the filler. I would try a different wire. 6061 welds fine!



              • #8
                Weld Alum.

                I have tig welded and machined a lot of alum. over the years. The 6061 welds very well. The main problem is that the amount of heat it takes makes it dead soft, known as condition 0 in terms of heat treat. There will always be a line between the heat affected zone and the original material, but this can be minimized as outlined above.
                The best way to cut it is with very sharp tools with a lot of back clearance and Tap Magic Aluminum for cutting fluid. Some people don't like the smell, but I think it has a pleasant cinnamon smell.
                I think I would try to find a way to press fit or thread a piece on without welding. The welded area will be weaker than the rest of the block. LocTite is your friend.
                Kansas City area


                • #9

                  1) don't kick the cat ( he didn't cut the part off)

                  2) don't throw something ( you will have to find it or pick up the pieces)

                  3)don't pout around the "old lady" (she can get even once a month)

                  So it is time to either weld it, bolt it or start over. If welding it,try the mentioned hammer process. If you can't get the finish you want, then it might have to be painted. Some painted parts along with polished parts can look great. If there is room to redesign and bolt/screw the part on it might look like it was designed that way. Starting over would be my last choice and only if I totally screwed up the weld.

                  We have all been where you are and can understand how you feel. I have learned to wash the car, dig a ditch, rake leaves or take a walk when I have made a large screw-up. Somehow this helps work out a solution to the problem.



                  • #10

                    Hello Dan, I have a tube of the material below and it works well for small aluminum welds. After it cools, it is remarkably strong and *seems* much harder than aluminum. I've never machined it, but I have tried to file seams with little success. I'm no metallurgist so unfortunately I really can't provide any critical analysis, but it may be worth looking into. Perhaps someone else with more experience can provide some insight.

                    I understand that Harbor Freight carries a similar product that they sell by the rod, but I've never used it.



                    • #11
                      This is a cool chart......and they are neighbors to Village Press


                      • #12
                        Thanks for the help guys... I think I'll just weld it up and machine it as normal and hope for the best... sounds like that's really about my only option. I'll make sure to engage my brain the next time I'm at the saw


                        • #13
                          I know what you mean by the smear. Nice and shiny in the virgin material, but nasty looking where the material lost its hardness. I don't know if it is an option for you, but what I have done in the past is run the lathe backwards against the cutter to burnish the material. It blends it in nicely, but use good amount of oil while doing it.
                          Eric Sanders in Brighton, Michigan


                          • #14
                            Just weld it up and machine away, 6061 welds fine. Use WD-40 and sharp tools with lots of rake and clearance when machining welds in aluminum. Tap Magic will work as well but I can't stand the smell.

                            Tom's Techniques