Cast Aluminum Welding - Tips for Tig Welding Cast Aluminum...there are 3 videos on this page 

Video #1 Tig Welding A Cast aluminum boat motor part

see more tig welding aluminum videos or go to the main TIG welding page

Video #2 Q&A on Tig Welding Cast Aluminum

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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 details about the cast aluminum welding repair in the videos 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 #3 tig weldng a small cast aluminum gun part

Why does cast aluminum weld like Fidos Butt?

Cast aluminum welding is sometimes difficult 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

Q&A on Tig Welding Cast Aluminum

Q: What filler rod did you use for this repair?

A:  I used 4043 for the actual part.

but a few days after I did the weld repair, I got some 4943 filler rod.

I decided to mock up some arc shots for the thicker parts of the jet pump  and I hogged out some sections of thick aluminum that would resemble the thick areas on the part.  I used 4943 to fill in those thick areas and it wet out very well.

Q: I am disabled and unable to use a foot pedal.

Are there any other options like torch mounted torch amperage controls?

A: Yes there are some other options. Quite a few actually.

I just happened to have some Ck Worldwide torch mounted amperage controls on the shelf and I will show some options...

there are north south slide switches, east west dials, and all kinds of other options.

for a guy like me who prefers a foot pedal, any of these would take a bit of getting used to in order to feel comfortable.

but I know its possible because I see awesome welds posted all the time from welders who use torch mounted amperage controls.

Q:I cant buy that dye check where I live so I use kerosene mixed with food coloring in a spray bottle.  for the developer, I use Dr. Shcolls athletes foot spray and it works great.

A: that sounds like something I would do.

I am definitely going to try that.

Q:Are you going to fabtech this year in Vegas?

A: Yes I am

Q: what were the machine and amperage settings for this weld repair?

A: amperage was set to either 175-200 and I used a foot pedal.

I would guess I was at about 175 for the thick section and 140 amps for the thinner areas.

ac balance set to 35% cleaning, ac frequency set to 80hz, using a #6 cup with around 15 cfh argon.

Q: what is your favorite tig rod for cast aluminum welding?

A: I like the new 4943 rod...but I think my favorite go to rod is still 4047 due to its lower melt point and the way it flows at such a low heat.

thats a real benefit for tig welding aluminum castings.

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