What's inside
As an Amazon Associate I earn from qualifying purchases. This post may contain affiliate links at no extra cost to you.
Repairing a cast aluminum housing is a demanding TIG job. The casting may contain oil, paint, corrosion, sand, porosity, and inclusions that were trapped during manufacture. A weld can look clean on the surface and still leak when the housing is put back into service. The welder matters, but preparation, heat control, and access usually matter more than buying the most expensive machine.
What to Look For in a TIG Welder
For cast aluminum, choose an AC/DC TIG welder with high-frequency start, adjustable AC balance, and adjustable AC frequency. AC is necessary because it provides the cleaning action that breaks up aluminum oxide. DC TIG is useful for steel, stainless, and copper, but it is not the right choice for normal aluminum repair.
A practical minimum is about 180 to 200 amps of AC output. That covers many small covers, brackets, pump bodies, gearbox housings, and motorcycle or automotive parts. A 250-amp machine gives more reserve for thick sections and large castings, but it will not automatically produce better welds. Extra amperage mainly helps you reach a stable puddle without running the welder continuously at its limit.
Look for a duty cycle of at least 40 percent at the machine’s rated output. A welder advertised at 200 amps may only deliver that output for a short period before its thermal protection activates. For occasional repairs, this is usually acceptable. For repeated industrial work, a 60 percent or higher duty cycle is worth paying for.
Best Welder Categories for Cast Aluminum Repairs
| Welder type | Best use | Advantages | Limitations |
|---|---|---|---|
| 200-amp AC/DC inverter TIG | Most garage and repair work | Portable, efficient, precise controls, usually affordable | Limited reserve on large castings; some have small torches |
| 250- to 300-amp AC/DC TIG | Thick housings and frequent repairs | More heat capacity, better duty cycle, larger torch options | Higher price, heavier, requires a stronger circuit |
| AC/DC TIG with pulse | Thin walls, heat-sensitive parts, controlled repairs | Reduces heat input and helps manage distortion | Pulse is not a substitute for correct cleaning and technique |
| DC-only TIG or AC/DC stick welder | Steel and general fabrication | Often inexpensive and versatile for other work | Not suitable for quality aluminum TIG repairs |
For most owners, a 200-amp AC/DC TIG welder is the sensible starting point. A budget inverter can be perfectly adequate if it has stable AC output, a foot pedal, gas pre-flow and post-flow, and usable balance and frequency controls. The cheaper option is fine for a few repairs each year, especially when the parts are under 6 mm thick and you already have a suitable 240-volt circuit.
Move up to a 250-amp AC/DC TIG welder if you repair large housings, weld for long periods, or commonly work on sections 10 mm or thicker. These machines also tend to have better cooling, larger torches, and more useful control over waveform and AC frequency.
Useful Starting Settings
For clean 3 mm aluminum, start around 100 to 130 amps. For 6 mm material, begin around 180 to 220 amps, depending on joint design and how much heat the casting absorbs. A rule of thumb of roughly 1 amp per 0.001 inch of aluminum thickness is only a starting point; castings vary greatly in conductivity and mass.
Set AC frequency around 80 to 120 Hz for general repair work. Higher frequency tightens the arc and improves control on small joints, while lower frequency produces a broader, softer arc that can help heat a larger area. Set AC balance near 70 to 75 percent electrode-negative as a starting point. If the surface remains heavily oxidized, use more cleaning action, but excessive cleaning reduces penetration and can overheat the tungsten.
Pulse is useful on thin walls and edges. Try a peak current of 100 to 140 amps, a background current of 30 to 50 percent, and one to two pulses per second. These are starting points, not fixed recipes. Watch the puddle and adjust for the casting’s thickness and heat sink effect.
A foot pedal or fingertip amperage control is strongly recommended. Castings often demand more current at the beginning and less as they heat up. Fixed-current machines make that transition harder and increase the risk of burning through a thin wall.
Preparation Determines the Result
Remove every trace of oil before welding. Heat the housing gently to draw oil out of pores, let it cool, then degrease it with a residue-free solvent. Do not weld over brake cleaner, chlorinated solvents, paint, or unknown cleaners. Some products can produce toxic gases when exposed to an arc.
Grind or machine the damaged area back to bright metal, extending beyond visible cracks. Use a dedicated stainless-steel brush only for aluminum, and brush immediately before welding. A carbide burr is useful for opening a crack into a shallow V, but avoid smearing contaminated metal across the repair.
Preheat large castings to roughly 120 to 175°C (250 to 350°F), checking with temperature-indicating crayons or an infrared thermometer. Preheating helps the puddle form and reduces the time spent at high amperage. Do not overheat unknown alloys; excessive temperature can worsen porosity, distort machined surfaces, or damage seals and heat-treated areas.
Torch and Consumable Choices
A water-cooled torch is valuable above about 200 amps or during long repairs. An air-cooled torch is simpler and cheaper for occasional work, but it becomes uncomfortable and may overheat when run near its rating. Choose a gas lens, a sharp 2.4 mm lanthanated tungsten, and 100 percent argon. Begin with argon flow around 15 to 20 cubic feet per hour and increase it only when drafts or a large cup require it.
ER4043 filler wets easily and is often a good choice for cast aluminum because it flows at a relatively low temperature. ER5356 offers higher strength and better color match in some applications, but it can be less forgiving and is not suitable for every alloy or service environment. If the housing carries structural loads, pressure, fuel, or corrosive chemicals, identify the base alloy and verify the filler choice rather than guessing.
Common Failure Modes
Porosity usually comes from oil, moisture, poor shielding, a dirty filler rod, or gas turbulence. Cracking can result from the wrong filler, excessive restraint, contamination, or welding an alloy that is not readily weldable. Lack of fusion occurs when the casting is too cold, the joint is too tight, or the oxide layer was not removed.
After welding, inspect the repair for pinholes and undercut. For a leak-prone housing, pressure-test it gradually with the appropriate fluid or low-pressure air and soapy water; never exceed the component’s safe test pressure. Machine or sand the repair only after it has cooled completely. A welder with good AC controls helps, but it cannot compensate for contaminated cast metal or an unidentified alloy.