Understanding the Differences Between AC and DC TIG Welding

Gas Tungsten Arc Welding (GTAW), or TIG welding, is a process that professional welders and engineers rely on for its precision and control. The choice between Direct Current (DC) and Alternating Current (AC) directly impacts weld quality, arc behaviour, and which materials can be joined effectively. For workshop operators, choosing the right current type and the correct equipment, such as DC or AC/DC capable welding inverters, determines how efficiently tasks are completed.

This article explains the technical differences between DC and AC TIG welding, highlighting real-world applications and product examples like the Strata EziTig200DCi and EziTig200ACDCi. It provides insights into polarity, arc control, and material suitability—essential knowledge for welders working with steel, stainless, aluminium, and more.

Understanding TIG Welding Polarity in DC Mode

The current type and polarity in TIG welding affect arc characteristics, heat distribution, and penetration. DC TIG welding uses a single, steady flow of current and can be configured in two polarity modes: DC Electrode Negative (DCEN) and DC Electrode Positive (DCEP).

DCEN (Direct Current Electrode Negative)

DCEN, or straight polarity, connects the tungsten electrode to the negative terminal and the workpiece to the positive terminal. Approximately 70% of the arc heat is concentrated on the workpiece and 30% on the tungsten electrode.

This polarity is standard for welding steels and stainless steels. It ensures deep weld penetration, low tungsten heating, and excellent arc stability. These features make it the preferred method for most ferrous metals, offering a clean, narrow bead with good fusion.

The Strata EziTig200DCi 200A TIG/ARC Inverter Welder is built for this kind of work. This unit combines the power of a 200A output with advanced IGBT Inverter Technology, delivering a smooth, stable DC arc suited for professional-grade TIG and ARC welding on mild steel and stainless components.

What sets the EziTig200DCi apart is its dual start modes, offering both Lift TIG and High-Frequency (HF) ignition. The HF start allows touch-free arc starting, reducing tungsten contamination and ensuring precise arc control. This feature is beneficial when working near sensitive electronics or in demanding fabrication settings.

The Cold Arc and Spot-Welding modes are proper for delicate work. These features allow welders to work on fragile materials without a filler rod, significantly reducing the risk of distortion and heat damage. This makes the machine ideal for fine fabrication, stainless sheet work, or ornamental welding.

At only 12.5kg, the EziTig200DCi is lightweight and portable, yet packed with innovative features like a digital microprocessor for accurate control settings, innovative cooling fan technology for quieter operation, and quick-connect gas fittings for hassle-free setup. It’s built for field or site work, with proven generator compatibility and rugged internal protection — production tested at 440V to handle real-world power fluctuations.

Whether you're in fabrication, light engineering, site maintenance, or general workshop work, the Strata EziTig200DCi offers a robust, efficient, and precision-focused welding solution — built to perform in the most demanding environments while maintaining control and comfort for the user.

DCEP (Direct Current Electrode Positive)

DCEP, or reverse polarity, connects the tungsten to the positive terminal and the workpiece to the negative. This setup shifts the heat balance, with 70% of the heat focused on the tungsten electrode and 30% on the workpiece.

While DCEP is rarely used for TIG welding, it plays a niche role. The intense heat on the electrode risks melting the tungsten, leading to tungsten contamination in the weld pool. However, during the positive half of the arc, DCEP helps break down aluminium oxide—an otherwise stubborn barrier on aluminium surfaces.

Due to the risk of overheating, DCEP alone is not practical for welding. Instead, the oxide-cleaning benefit of DCEP is combined with the penetration advantages of DCEN in AC TIG welding.

AC TIG Welding: The Solution for Aluminium and Magnesium

Alternating Current (AC) TIG welding is essential for non-ferrous metals like aluminium and magnesium, which form oxide layers that inhibit welding. In AC mode, the polarity alternates rapidly between electrode negative and positive. Each complete cycle contains one positive and one negative half. Standard AC frequency in New Zealand is 50 Hz, meaning the current switches polarity 100 times per second.

During the electrode-positive phase, the arc breaks down aluminium oxide. Heat is directed into the base metal during the electrode-negative phase, creating penetration. This dual action allows clean, strong welds on aluminium without pre-grinding or chemical cleaning.

A key benefit of AC TIG is that it eliminates arc blow, where the arc wanders due to magnetic forces, particularly in DC welding of magnetised steel. By constantly reversing polarity, AC prevents magnetic buildup.

Sine Wave vs Square Wave

Traditional TIG machines generated a sine wave AC output, where current flows in a smooth, rounded pattern. While functional, sine wave AC has gradual transitions through zero, which can lead to arc instability, inconsistent arc starts, and less control, particularly in aluminium welding.

Modern inverter-based machines like the Strata EziTig200ACDCi use square wave technology, which transitions sharply between polarities. This produces a more focused, crisper arc with longer peak amperage time, enhancing penetration and arc stability. The result is better weld puddle control, especially beneficial when working on aluminium or magnesium alloys that form stubborn oxide layers.

AC Frequency and Balance Control

High-performance TIG welders such as the EziTig200ACDCi offer adjustable AC frequency and AC balance control, which are key features when welding aluminium.

• Increasing AC frequency narrows the arc cone, allowing welders to focus the arc more precisely, reduce the heat-affected zone (HAZ), and weld tight joints or intricate parts with greater control.
• AC balance control lets users fine-tune the time spent in electrode-negative (EN) and electrode-positive (EP) cycles. EN promotes penetration and protects the tungsten, while EP assists in cleaning oxidation off the material surface — essential when working with dirty or cast aluminium.

The EziTig200ACDCi includes these advanced adjustments, enabling operators to customise the arc profile to suit their jobs, whether detailed fabrication or heavy-duty repair.

The EziTig200ACDCi is a fully featured AC/DC TIG and MMA welder designed for high-performance welding in both aluminium and steel. With a powerful 200A output, it delivers smooth arc characteristics, supported by IGBT inverter technology for efficient, stable performance.

Key Capabilities and Features:

• AC and DC pulse welding for versatile material compatibility
• Spot welding mode for thin sheet materials — perfect for decorative or precision work where heat input must be tightly controlled
• Lift TIG and HF TIG start modes, ensuring reliable ignition in both sensitive electronic environments and rugged field conditions
• 2T/4T and Bi-Level trigger modes for adaptable operation across short and long weld runs

Whether you're working on thin aluminium panelling or structural stainless fabrications, the EziTig200ACDCi allows users to adapt the machine to their needs with remote control options, including a wired foot pedal, torch-mounted up/down control, or thumbwheel potentiometer (optional).

Designed with the job site in mind, the EziTig200ACDCi combines a rugged, corrosion-resistant casing with an intelligent cooling system, which protects internal components from environmental contaminants and reduces fan noise. Weighing in at a manageable size, it’s compact and portable, making it ideal for workshop and mobile use. The welder is generator-friendly, tested under 440V conditions, and backed by an Intelligent Machine Protection System to guard against voltage spikes and overheating.

Whether you're a fabrication specialist, a mobile welder, or a technician working with various materials, the Strata EziTig200ACDCi offers the precision and power to meet demanding projects head-on. Its combination of modern waveform control, pulse capabilities, and innovative operational modes makes it an excellent investment for any serious welding setup.

Choosing Between DC and AC/DC Welders

For Steel and Stainless Steel

A DC-only TIG welder is suitable if your work involves steel, stainless steel, or other ferrous materials. DCEN provides excellent penetration and arc control.

The Strata EziTig200DCi is designed for this purpose. It weighs just 12.5 kg and is portable and robust, suitable for on-site welding or factory-based operations. It includes generator-friendly features and a fan-on-demand cooling system for reliability in industrial settings.

For Aluminium and Mixed-Material Applications

An AC/DC TIG welder is essential to weld aluminium or magnesium. Aluminium oxide requires the cleaning action of the AC positive half-cycle. The Strata EziTig200ACDCi provides this capability, with waveform and pulse controls for even more versatility.

It includes spot welding mode and pulse TIG functionality, making it ideal for thin aluminium jobs and improving control on thicker sections. Whether you’re building aluminium structures, repairing marine components, or fabricating heat exchangers, this machine delivers the required performance.

Both Strata models support foot pedal control, allowing the welder to adjust amperage in real time. This is vital during long weld runs or welding parts with varying thicknesses.

Pulse TIG mode, available on both models, allows fine heat management. In this mode, the machine alternates between high and low amperage at a set frequency, allowing the weld pool to cool between pulses. This helps control HAZ and avoid distortion on thin materials.

Spot welding mode adds further control for short, repeatable welds—ideal for tacking or joining thin sections without overheating.

Avoiding Common Problems in TIG Welding

Tungsten Contamination

Contamination of the tungsten electrode by contact with the weld pool can cause inclusions and arc instability. Using HF start reduces the chance of tungsten touching the base metal. A pointed tungsten is best for DC, while a slightly ball-ended tip is suitable for AC.

Arc Instability

Poor arc stability results from fluctuating arc length, electrical noise, or improper polarity. The correct start method, clean tungsten, and proper shielding gas flow ensure a consistent arc. The Strata machines use a high-frequency (HF) to create a clean arc without contact. This reduces contamination and improves arc control, especially in AC welding.

Managing Heat-Affected Zone (HAZ)

The heat-affected zone is the area of metal that changes properties due to welding heat. Using pulse mode and higher AC frequency narrows the arc and limits HAZ, which is especially important in precision fabrication or cosmetic welding. Modern TIG inverters, like the EziTig series, help reduce HAZ through advanced waveform control and real-time adjustments during welding.

Application Summary

• Steel and Stainless Steel: Use DCEN with a machine like the Strata EziTig200DCi for consistent penetration and stable arc control.
• Aluminium and Magnesium: Use AC with an AC/DC machine like the Strata EziTig200ACDCi. Use balance and frequency controls to tailor the weld to the job.
• Thin Sheet Metal: Use pulse TIG mode and spot welding to control heat and prevent distortion.
• Contaminated or Oxidised Surfaces: Rely on the cleaning action of the AC positive cycle, or pre-clean the metal surface before DC welding.

The choice between AC and DC in TIG welding directly affects your ability to weld different materials effectively. DC, particularly in DCEN configuration, is the go-to for ferrous metals due to its deep penetration and stable arc. AC is required for aluminium and magnesium, enabling oxide cleaning and controlled fusion.

Proline Industrial supports New Zealand’s welders and engineering professionals by offering expert advice and a trusted range of equipment. For those looking to expand their capabilities or refine their weld quality, now is the time to explore the full features of Strata’s TIG/ARC inverters. Choose the right welder for your work—and let Proline Industrial help you weld confidently.