Use AC (Alternating Current) TIG welding for aluminium and magnesium, because it helps remove the oxide layer during welding. Use DC (Direct Current) TIG welding for steels, stainless steel, copper, titanium and most other metals. Choosing the correct current type is essential for achieving good penetration, arc stability and weld quality.
AC vs DC TIG welding — what’s the difference?
AC TIG welding is used primarily for aluminium and magnesium because the alternating current helps break up and remove the oxide layer that forms on these metals during welding. DC TIG welding is used for steels, stainless steel, copper, titanium and most other metals. Selecting the wrong current type will compromise penetration, arc stability and the overall quality of the weld, so it is one of the first decisions to get right.
This is also why machine choice matters: DC-only machines suit steel and stainless steel, while AC/DC machines add the capability to weld aluminium. For more on selecting a machine, see our guide to buying TIG welders and consumables.
What TIG amperage should I use?
The correct amperage depends on material type, thickness and joint design. Thin sheet requires lower current, while thicker materials require higher output for adequate penetration. Most welding machine manufacturers provide recommended amperage ranges for common applications, which is the best starting point for dialling in your settings.
For thin materials, low amperage combined with pulse TIG welding gives even finer control of heat input and helps reduce distortion.
Matching current and tungsten
Your current choice also drives your tungsten choice. Blue (2% Lanthanated) tungsten works well on both AC and DC, while Zirconiated (white) tungsten is geared towards AC aluminium welding. See our TIG tungsten electrode guide for the full breakdown.
Choosing the right TIG welder
If you are buying or upgrading a machine, base the decision on the materials you intend to weld, the required output current, and whether AC capability is needed for aluminium. AC/DC machines offer the greatest versatility. Our TIG welder and consumables buying guide walks through duty cycle, pulse functions and portability in detail.
If you need help matching current type, tungsten and filler to your job, the Weldability SIF technical team is happy to advise — get in touch.