Aluminum TIG topics
AC Alternating Current
AC Balance Control
AC Frequency Control
Aluminum Filler Metal
TIG Welding aluminum
TIG welding is one of the best ways to weld aluminum. It provides the necessary control to get a nice bead appearance. However, welding aluminum is much different than welding steel and other alloys. Why? First, it has a high melting surface oxide and it conducts heat very fast - making it difficult to form a puddle. On top of that, aluminum doesn't change color when heated so it's difficult to tell when it's ready to weld and take a trained eye to read the puddle.
Cleaning Aluminum: Remove the Oxides
Surface oxides exist on all metals. On steel we call is rust. On stainless steel, chromium oxide forms a protective layer that reduces corrosion. So why are oxides a problem on aluminum and magnesium?
It's quite simple. Aluminum and magnesium have high-melting surface oxides. That is, they melt at a higher temperature than the base metal. In order to weld aluminum and avoid the "water-bed" affect, it helps dramatically to clean the surface. There are 3 ways to clean your aluminum:
1. Mechanically: Use a stainless steel wire brush dedicated to aluminum for removing surface oxides. Brush the joint before you start and again between weld passes.
2. Electrically: That's right, use AC welding current to provide real-time surface etching that scrubs and removes the oxides around the weld zone. Some advanced applications actually run low current DCEP ahead of the welding arc just to clean the aluminum joint.
3. Chemically: This typically a last resort and reserved for ultra-high purity applications. But, you can use a chemical cleaner just prior to welding to help remove oxides. However, you should only use approved cleaners and use a lint-free clothe to prevent causing more issues than you're solving. If you need to make x-ray quality welds and can't pass the test, you may need a chemical cleaner. Otherwise, there are NOT widely used or necessary.
When to Add Filler Metal
When you establish an arc on aluminum, the first thing you'll notice is etching or cleaning action. Keep adding heat until you see a nice shiny weld puddle form. Once the puddle forms and reaches the desired width, you can begin to add filler metal. Follow these steps for good results:
1. Allow a puddle to form & keep adding heat until you see a round, mirror-like appearance directly beneath your torch.
2. Make sure you dip the filler metal into the puddle & allow the puddle to melt the rod.
3. Quickly dip the filler in the puddle and retract it away from the arc. The heat of the arc can cause the filler rod to oxide or ball up before it reaches the weld puddle.
4. Never rest aluminum filler metal on the part - it conducts heat rapidly and will oxide or ball back due to the conductive heat from the base metal.
5. Use a steady rhythm - even try counting in your head to get a consistent ripple pattern in your weld bead. Like a musician, you need to monitor and maintain your timing.
6. Don't forget to move! Once the puddle is formed, you need to push it along. If you stay in the same place for too long, your puddle will get too wide and eventually you will melt through the aluminum. So, monitor your heat by keeping a uniform puddle width as you travel along the weld joint. If the puddle gets too wide - use less amperage or pick up your travel speed.
AC vs. DC
In the beginning, AC machines were very unreliable. So, DC was used for almost every application - including aluminum. DCEN (direct current electrode negative) was used for most applications with 100% helium. That produced good welds but heat input was difficult to control, it required lots of pre-cleaning and helium was expensive. DCEP (direct current electrode positive) was also used, and although it produced an etching or cleaning action - it heated, balled and eroded the tungsten severely even at low amperages.
So, AC machines were improved which provided the best of both worlds. High frequency current was added to the units in order to stabilize the arc - because it wanted to go out every time the polarity changed which would cause annoying instability. Argon was also found to produce better results at a lower cost than helium, so the process benefitted all around from the use of AC TIG machines.
Tips for adding filler:
Dynasty setup guide:
This Dynasty setup guide covers need-to-know info for anyone who is welding aluminum with an inverter welding machine like this popular model.