The difficulty of removing the oxides makes soldering aluminium difficult. Aluminium conduit, made from 6xxx series aluminium with a magnesium alloy, poses a more difficult problem. According to a 2010 article by A. E. Gickler in the American Welding Society's online magazine, "the 6xxx (silicon and magnesium added) series may or may not be solderable depending upon the individual alloy." And since aluminium thin wall tubing (EMT) isn't designed to be soldered, you have to experiment to see if you can solder your particular alloy.
- Skill level:
Things you need
- Soldering flux
- Soldering torch
Clean off any dirt, paint, oil or grease from the conduit with solvent and a rag.
Apply flux to the areas to be soldered. Place the surfaces so that they are touching, since solder will not fill gaps.
Thoroughly heat the area with your torch.
Touch your solder to the aluminium joint. If the solder melts instantly, the joint is hot enough. If not, continue heating. Do not melt the solder with the torch. The hot aluminium has to melt the solder directly.
Watch the solder as it melts. If your flux and solder suit your particular alloy, the solder should flow onto the aluminium and seep into the joint. If it just rolls off, experiment with different fluxes and solders. There is no guarantee you will find a solder that works.
Tips and warnings
- Try an organic amine-based flux or an inorganic chloride or fluoride flux with a soft solder made of 95 per cent tin and 5 per cent zinc. You can also try a complex fluoroaluminate salts flux with zinc-based hard solder.
- Allied Aluminum makes a thin wall of 6005 series aluminium, and rigid conduit of 6063, but does not give soldering specifications on its data sheet, as it is not designed to be soldered. It does provide coupling hardware.
- EMT stands for electrical metal tubing.
- Since aluminium has a relatively low melting point, overheating it may cause it to warp. Only heat it enough to melt the solder.
- Work in a well-ventilated area, because your solder and fluxes may give off toxic fumes.
- Even if you are successful in soldering aluminium thin wall with a tin-based solder, it may slowly react with the aluminium and corrode over time.
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