Cast Aluminum Welding - Tips for Tig Welding Cast Aluminum 

Cast aluminum welding repairs can be tricky.

For the most part, the level of difficulty depends on the service environment the part was subjected to.

For example, aluminum can be exposed to fresh water, salt water, exhaust gas carbon, oil, and other nasty things.

The worst cast aluminum weld repairs are usually due to oil or exhaust gas carbon....or a blend of the 2.

A few fun facts about the cast aluminum welding repair in the video above...

cast aluminum welding repair jet pump housing
  • Its a jet pump for an outboard boat motor that hit some rocks and made some extensive cracks.
  • The owner of the boat is a machinist and so was able to face off the flange and redrill and tap the threaded holes and replace studs.
  • The repair was done as a favor...If I were doing this repair for a customer I probably would have charged around $200

Things to do to make a cast aluminum weld repair go better

  • 3 c's  Clean...Clean...Clean
  • Preheat part to around 200f
  • Carbide burrs designed for aluminum are best bet for grooving out cracks but grinding wheels work too ( Sometimes I use Irish Spring bar soap to prevent loading of a grinding or sanding disc)
  • if you have AC balance, a setting of 65 or less EN helps ( since some machines have use a scale of cleaning on AC balance, a setting of around 35% cleaning works good)
  • Sometimes you have to be willing to remove crapped up weld metal...the next pass usually goes better after you do this.
  • A cleaning pass helps...where you allow the cleaning action of the arc to etch the surface before you actually puddle the metal.
  • think braze...use a forward and back torch motion to gently flow weld metal ahead using just enough amperage to flow the puddle
  • 4047 weld rod can really help but it is slightly softer than 4043.
  • 4047 usually gets less porosity so that can help on things like polished crankcases

video of a small cast aluminum repair on a gun piece

Why does cast aluminum weld like Fidos Butt?

Cast aluminum welding is hard because castings have impurities.

Oil soaked castings like crankcases from motorcycles, machinery parts, or even cookware, can give you fits. As soon as you strike an arc, you can see crap boiling to the surface.

When heat is applied, small voids become like little pressure cookers and the gas will try to escape somewhere. Mostly in the molten aluminum puddle and the gas gets trapped as bubbles as the aluminum solidifies....and becomes porosity.

Where does porosity come from?

Porosity is gas bubbles....plain and simple..but what is not so simple is what causes those gas bubbles.

The gas can come from lubricants, abrasive grit, moisture, hydrogen, oxides, etc.

Sometimes it is very hard to know exactly what causes porosity.

Sometimes its something as simple as the level of humidity.

Sometimes its a thick layer of oxide...or a rough sheared edge. Determining the exact cause of porosity can be like chasing a ghost.

What is the best tig rod for cast aluminum?

here is a little known resource for selection of tig welding rods for cast aluminum

5356 is stronger than 4043 but tends to get porosity when used to weld aluminum castings.

4043 is fine and usually a pretty good choice for castings because the silicon content makes it a close match for most aluminum castings.

Maxals  4943 is a fairly new alloy that is touted as a great replacement for 4043 on aluminum castings.  it works pretty good.

But in my opinion, 4047 usually is better for preventing porosity.


Because of the higher silicon content.

Silicon is a deoxidizer but also lowers the melting point of aluminum alloys.

A lower melting point means the filler wire will flow at lower amperage...and that means it will be less likely to draw impurities out of the cast aluminum base metal.

4047 aluminum filler wire contains around 12 % silicon and although has a slightly lower tensile strength than 4043, tends to make welds that have considerably less porosity than welds made using 4043 filler metal.
see more videos on aluminum welding