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mixing metals

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  • mixing metals

    I know some of you will have the answer to this question- what are the best screws\bolts to use when fastening metals? I generally fabricate in aluminum, and some of the applications are meant to live outdoors, in the rain, and with temperature changes. Will stainless hardware be the best option with al, and how strong are they compared to the options,(socket head bolts, ordinary chromed or zinc plated bolts, or brass hardware) How well will socket head bolts stand up to wet, esp in contact with aluminum? Will I be ok to use socket head bolts outside if I wax them before use? Mostly I will be joining al to al, and welding is not an option for the most part.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    You shouldn't have any trouble with the s/s fasteners.Just remember to use never-sieze to prevent galling.Never combine steel and aluminum because of electrolisis as well as other combinations such as aluminum/copper.The zinc plated are fine for indoor use but will rust outside in the rain.While the s/s is good for about grade3-5 tensile strength(55,000psi) the fatique stength is greater.I try to stay away from hot dipped galvinized in the smaller sizes because the strength is poor at best.If you want to save some money on the s/s fasteners try ebay.
    I just need one more tool,just one!


    • #3
      When I worked for Kenworth Sales for several years there was a popular use of Aluminum frame members in Trucks. I think that is completely over now. It was a common situation with the steel brackets and the bolts used, that the bolts would have to be broken off and drilled out. I think the aluminum and aluminum oxides will migrate toward the steel and bind the threads on a molecular level and sieze the bolts. Dissimular metals create the electrolysis problem. You may be able to use steel bushings or inserts where the binding becomes an asset to overcome the problem.
      Good Luck.


      • #4
        Aluminum is normally hard anodised when minimal electro-chemical interaction is required. Otherwise use the Stainless steel and antiseize - use it on your wheel lug nuts and the nut face too!


        • #5
          Here's a link to a galvanic series chart. For any two metals touching or even very near each other in a moist environment, the one higher on the chart will corrode, and the farther apart they are on the chart, the worse the corrosion will be. Other charts, with perhaps more explanation, are available on the net. Search for "galvanic series".

          [This message has been edited by Uncle Dunc (edited 02-04-2003).]


          • #6
            Thanks for the input. I must remember to get some anti seize, I want to try it for tapping in stainless, amongst other things. The galvanic series is interesting. I can see how zinc and copper would make a somewhat energetic battery of sorts, now add the drano-- hey, didn't we do this in school a few yarn ago? So long ago.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


            • #7
              You might also try the anti-oxidant grease that electricians use on aluminum service entrance wiring. It keeps the aluminum from oxidizing and eventually creating a bad connection, which will result in arcing and a fire.