Table of Contents

1. Introduction: Friction Stir Welding, MIG/TIG Welding and Aluminum Alloy Welding

2. Key Differences Between FSW, MIG Welding and TIG Welding

3. Metallurgical Quality in Aluminum Alloy Welding: Core Evaluation Indicators

4. Porosity Control: A Critical Challenge in Aluminum Alloy Welding

5. Performance Comparison: FSW vs MIG Welding vs TIG Welding

6. Industry-Related FAQs

1. Introduction: Friction Stir Welding, MIG/TIG Welding and Aluminum Alloy Welding

Aluminum alloy welding is a critical process in aerospace, automotive, and construction industries. Its demand keeps growing as lightweight materials become more popular.

Three common techniques dominate this field: friction stir welding (FSW), MIG welding (Metal Inert Gas Welding), and TIG welding (Tungsten Inert Gas Welding). Each has its own strengths and weaknesses.

The global aluminum welding market was valued at $8.2 billion in 2025, and is projected to grow at a CAGR of 5.3% from 2026 to 2033. Metallurgical quality and porosity control are the two most important factors that determine the reliability of aluminum alloy welds.

This article compares FSW, MIG, and TIG welding, focusing on how they perform in terms of metallurgical quality and porosity control for aluminum alloy welding projects.

2. Key Differences Between FSW, MIG Welding and TIG Welding

2.1 Friction Stir Welding (FSW): Solid-State Welding Technology

FSW is a solid-state welding process, which means the aluminum alloy does not melt during welding. It uses a rotating tool to generate friction heat, softening the material and forming a joint through plastic flow.

Unlike MIG and TIG welding, FSW has no molten pool. This avoids many defects caused by melting and solidification.

It’s particularly suitable for high-strength aluminum alloys, such as 5083, 6061, and 7075 series, which are widely used in aerospace and automotive industries.

2.2 MIG Welding: High-Efficiency Fusion Welding

MIG welding is a fusion welding process that uses a consumable electrode to melt the base metal and filler metal, forming a weld joint under inert gas protection.

It’s known for its high welding speed and efficiency, making it ideal for mass production of aluminum alloy components.

However, the molten pool in MIG welding is prone to porosity and other defects if the process parameters are not properly controlled.

2.3 TIG Welding: High-Precision Fusion Welding

TIG welding uses a non-consumable tungsten electrode to create an arc between the electrode and the base metal, melting the aluminum alloy to form a weld.

It offers excellent welding precision and surface finish, suitable for thin-walled aluminum parts and high-precision components.

Its welding speed is slower than MIG welding, and it requires skilled operators to ensure consistent quality.

3. Metallurgical Quality in Aluminum Alloy Welding: Core Evaluation Indicators

3.1 What is Metallurgical Quality?

Metallurgical quality refers to the microstructural and mechanical properties of the weld joint. It includes grain size, heat-affected zone (HAZ) width, and joint strength.

For aluminum alloy welding, good metallurgical quality means fine and uniform grains, narrow HAZ, and high joint strength (close to the base metal).

3.2 Metallurgical Quality of Each Welding Process

FSW has the best metallurgical quality among the three processes. The friction heat and plastic deformation promote dynamic recrystallization, resulting in fine grains (10-20 μm) in the weld zone.

The HAZ of FSW is very narrow, usually 1-3 mm, which minimizes the softening of the base metal. The joint strength of FSW can reach 85-95% of the base metal.

TIG welding produces relatively fine grains (20-30 μm) due to its stable arc and slow cooling speed. Its HAZ width is 3-5 mm, and joint strength is 75-85% of the base metal.

MIG welding has coarser grains (30-50 μm) because of its fast cooling rate. The HAZ width is 4-6 mm, and joint strength is 70-80% of the base metal. Sometimes, it can be lower if porosity is present.

4. Porosity Control: A Critical Challenge in Aluminum Alloy Welding

4.1 Causes of Porosity in Aluminum Alloy Welding

Porosity is the most common defect in aluminum alloy welding. It is mainly caused by hydrogen absorption during the welding process.

Aluminum has a high affinity for hydrogen, which can come from moisture in the air, contaminated filler metal, or oil on the base metal surface.

When the molten aluminum solidifies rapidly, the hydrogen cannot escape in time, forming small pores in the weld joint. These pores reduce the joint strength and corrosion resistance.

4.2 Porosity Control Capabilities of Each Process

FSW has the best porosity control performance. Since it is a solid-state process, there is no molten pool, so hydrogen absorption is greatly reduced.

The porosity rate of FSW welds is usually less than 0.5%, which meets the highest industry standards. Some high-precision FSW processes can even achieve a porosity rate of less than 0.1%.

TIG welding has a moderate porosity control effect. Its porosity rate is generally 0.8-2.0%, thanks to the effective inert gas protection. But improper gas flow or contaminated electrodes can increase porosity.

MIG welding has the poorest porosity control among the three. Its porosity rate ranges from 1.8% to 5.1%, especially when the welding speed is too high. The fast welding speed leaves little time for hydrogen to escape from the molten pool.

5. Performance Comparison: FSW vs MIG Welding vs TIG Welding

6. Industry-Related FAQs

Q1: Why does FSW have better metallurgical quality than MIG and TIG welding for aluminum alloy welding?

A1: FSW is a solid-state welding process, no molten pool is formed during welding. This avoids defects like grain coarsening and segregation caused by melting and solidification. The friction heat and plastic deformation also promote dynamic recrystallization, resulting in finer grains and narrower HAZ, which improves metallurgical quality.

Q2: How to improve porosity control in MIG welding of aluminum alloys?

A2: First, ensure the base metal and filler metal are clean, free of oil, moisture, and oxide. Second, adjust the welding parameters—reduce welding speed to give hydrogen more time to escape. Third, use high-purity inert gas (argon) and maintain proper gas flow to ensure effective protection.

Q3: Which welding process is more suitable for high-precision aluminum alloy components?

A3: TIG welding is more suitable for high-precision thin-walled components, thanks to its excellent welding precision and surface finish. For high-strength thick-walled components that require good metallurgical quality and low porosity, FSW is the better choice.

Q4: What is the impact of porosity on the performance of aluminum alloy welds?

A4: Porosity reduces the effective cross-sectional area of the weld joint, which lowers its tensile strength and fatigue strength. It also creates stress concentration points, increasing the risk of crack initiation. In severe cases, porosity can lead to weld failure, especially in load-bearing components.