I thought you might like to see this short video showing what is involved in welding and machining repairs for aluminum cylinder heads.
This kind of repair is fairly common but it looks like Brodix has the process down pretty well. According to the video, they only repair Brodix parts. Not Mitsubishi, Not Hyundai, Not Kia.
That way They can be sure of the chemical composition of the aluminum before they start welding because they made the part to begin with. That is a big help.
Aluminum castings can be difficult to weld. No matter how clean you get the surface, there is always some contamination lurking in aluminum metal that has been in service and is impregnated with oil and carbon.
Aluminum heads are usually cast using 355, 356, a356 or 357 aluminum. All of which contain somewhere in the neighborhood of 5-8% silicon.
Some Cylinder head repair shops use matching filler metal when they know what they are welding, but an awful lot of shop just use whatever works.
4043 aluminum welding filler rod is the most commonly used general purpose aluminum rod for general stuff.
The newer alloy 4943 works almost the same except with somewhat better properties than 4043 and it can be heat treated.
For Castings like cylinder heads, a high silicon rod like 4047 is often chosen because of its lower melting temperature and fluidity along with less of a tendency to get porosity. In fact 4047 is often referred to as a brazing rod.
The 12% silicon content lowers the melting temperature and slows the shrinkage rate enough to help hot cracking and lessen the tendency for porosity. Repair shops that weld aluminum boat propellers often use the 4047 filler rod to avoid porosity on final finish.
A good tip for you if you weld aluminum castings with any regularity is to get yourself some 4047.
Another tip is to have 2 die grinders handy, one with a stainless wire brush and the other with a course carbide burr. Trust me on this one. you will need to remove tungsten, grind out porosity, and brush off soot when you dip your wick. Sometimes skimming the surface of beads reveals hidden porosity before final machining and save time and embarrassment in the long run.
A good preheat to about 200f helps a bunch too.
And for the best tip of all....Get some Argon/helium mix. 50/50 will do but even mixes with up to 80 percent helium sometimes work better. You can also by a Y valve and another regulator/flowmeter and a bottle of straight helium,and just mix it yourself but it is easier to just get the mix.
Check out the torch the tig welder is using in the video. It is a flex head, water cooled, gooseneck torch. Weldcraft makes one like this that is water cooled and the number is WP-25. It’s called a wp-25 flexible neck tig torch and it is really handy for welding down inside ports and in tight areas where a standard rigid torch just wont cut it.
Water cooled torches for welding heavy castings like this are a must.
There are at least 3 main things you have to watch out for when you do weld build up repairs like this on cylinder heads or anything else that will be re-machined after welding.
1. Tungsten….Imagine what happens on the final fly cut if the cutting tool grabs a hard tungsten inclusions
2. Putting on enough weld metal without adding too much. It sucks when you think you have built up enough but it does not quite clean up on final machining
3. Porosity. Sometimes you know when its in there…sometimes you don’t know until its dressed down.