I have this skateboard truck for my off-road skateboard. I want to mig weld a piece of aluminum to it to mount a motor. How would I test if it is something I can weld to with a MIG welder? I think it is aluminum, how can I be sure?

From what I understand

  • if magnets don't stick to it, it is aluminum.

  • if I test for continuity with my multimeter and I don't have continuity, it is probably anodized.

  • if it were polished it would be very shiny and probably reflect light.

How do tell if it is in fact annodized, and if so, what do I need in order to weld through it? Do I sand it down? I was going to use a flux core mig welder.

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For reflection

Also here is the inside where they have an existing weld. enter image description here

  • 1
    $\begingroup$ magnets don't stick to brass either $\endgroup$
    – Solar Mike
    Jun 17 '17 at 19:07
  • $\begingroup$ magnets don't stick (or stick much) to stainless steel either. $\endgroup$
    – agentp
    Jun 19 '17 at 19:13
  • $\begingroup$ or any other metal without iron in it… $\endgroup$
    – hdrz
    Jun 21 '17 at 7:13

That does look a lot like aluminium. All grades of aluminium are non-magnetic as are some stainless steels. The best test is weight as aluminium is significantly less dense than steel but has lower tensile strength so judging by the bulk aluminium seems likely. a final test is that if you grind aluminium with an abrasive wheel it will produce virtually no sparks.

I've not heard of flux core wire for aluminium, stick rods for aluminium alloys do exist but tend not to give great results in general.

Generally TIG is the best option for aluminium alloy welding but a decent MIG machine with pure argon shielding gas and the appropriate filler wire can produce good results. The difficulty with MIG is that aluminium wire is significantly softer than steel so tends to have more problems with wire feed.

Another issue is that not all grades of aluminium have good weldability this article gives good overview.

The other issue, which applies to welding any finished part is that the welding process inevitably puts a significant amount of heat into it which can affect its mechanical properties on a material level an also cause dimensional distortion, which can be mitigated but never entirely eliminated.

The short answer is that it may not be impossible to do but is likely to be considerably more difficult than just welding a bracket to bit of mild steel and modifying finished parts by welding is always a bit risky when you don't know the specific of their material and manufacturing process.

  • $\begingroup$ Thanks. I updated my question with a picture. On the inside they have a weld. Any idea what type of weld it would be? Using what type of welder? i.stack.imgur.com/NtGsC.jpg $\endgroup$
    – Johnston
    Jun 17 '17 at 23:25
  • $\begingroup$ This site : mig-welding.co.uk/aluminium-welding.htm suggests TIG is easier for those welders with less experience - mig tends to be used by production runs apparently. $\endgroup$
    – Solar Mike
    Jun 18 '17 at 5:55
  • $\begingroup$ I cant tell exactly what is in that last picture, definitely not a TIG weld though and looks more like sealant or adhesive that anything else. $\endgroup$ Jun 18 '17 at 9:44
  • $\begingroup$ @Johnston - I agree. Don't weld it. 1. Remove those bolts and get longer ones. 2. Get another piece of metal, flat or a bracket (angle iron) shape. 3. Drill holes in the new piece of metal and attach it to the truck to check it fits. 4. Remove it and drill additional holes to mount the motor. 5. Bolt it back on. 6. Bolt on the motor. --- Nothing damaged and easy to do. --- If you insist on welding do it on the other inexpensive piece of metal and not your trucks. --- Welds not correctly made will break. $\endgroup$
    – Rob
    Oct 2 '18 at 12:32

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