Lightweight, resistant to rust, and easy to process—. Aluminum is a metal material used in a wide range of fields, from automobiles, aircraft, and electronic devices to building materials and household goods, thanks to these characteristics. In recent years, demand has accelerated further due to the shift to EVs (electric vehicles) and the growing need for lighter-weight components.

However, “easy to process” does not mean “easy to weld.”

In reality, because it has different properties from iron and stainless steel, welding aluminum requires advanced skills and specialized knowledge.

Compared to iron and stainless steel, welding aluminum is more difficult in the following respects:

Due to these factors, it is often said that “welding aluminum is difficult.”

This article explains the fundamental knowledge and practical techniques for successful aluminum welding.

The content will be particularly beneficial for the following individuals:

Starting with “why it’s difficult,” this article will explain the differences between welding methods like TIG and MIG, suitability by material and application, and common failures and their countermeasures, using examples and diagrams.

Even those with experience welding iron and stainless steel will often feel that “aluminum is a different beast.” Here, we will explain the fundamental reasons why aluminum welding is difficult from four perspectives.

Aluminum is characterized by a low melting point of 660°C and extremely high thermal conductivity. Specifically, its thermal conductivity is about 237 W/m·K, approximately three times that of iron (about 80 W/m·K).

Furthermore, aluminum’s coefficient of thermal expansion is 23.1×10⁻⁶/°C (at 20-100°C), nearly twice that of iron (about 11.7×10⁻⁶/°C). For this reason, arc heat tends to spread rapidly throughout the entire base material, making burn-through and thermal deformation outside the weld zone more likely to occur.

Especially in the welding of thin aluminum sheets, the bead often collapses, creating holes, making the operator’s torch handling and current settings crucial.

Aluminum is highly reactive with oxygen in the air, forming an oxide film (Al₂O₃) even at room temperature. The melting point of this film is about 2,000°C, which is much higher than the base material, so it does not melt with normal heating and interferes with welding.

To resolve this:

These methods are effective. In AC mode, the polarity alternates, and the oxide film is broken down on the positive side, which stabilizes bead formation.

Defects specific to aluminum welding include “weld cracking” and “blowholes (pinholes).”

To mitigate these risks, utilizing a pulse function, using a mixed gas (Ar + He), and performing preheating and degreasing treatments are effective.

For example, A5052 (Al-Mg series) contains 2.2-2.8% Mg and has excellent corrosion resistance and weldability. On the other hand, A6063 (Al-Mg-Si series) contains 0.2-0.6% Si and 0.45-0.9% Mg; while suitable for extrusion, care must be taken to prevent weld cracking.

Furthermore, the high-strength material A7075 (Al-Zn-Mg series) reaches a tensile strength of about 572 MPa with T6 heat treatment and is used in the aerospace and automotive sectors.

Especially for DIY purposes, choosing a grade with high weldability like A5052 is considered a safe bet.

For welding aluminum, it is important to choose the optimal method according to the thickness, shape, and application of the base material. Here, we will explain the features and application scenarios of three commonly used welding techniques.

TIG (Tungsten Inert Gas) welding is a method that uses a non-consumable tungsten electrode and protects the arc and weld zone with an inert gas like argon. It is ideal for situations requiring a precise and beautiful finish. It does not produce spatter or slag, allowing for very clean welding. It is particularly suitable for joining thin sheets or small-diameter pipes, as well as for DIY and one-off repairs. A key feature is the ability to work in AC (alternating current) mode to break down the oxide film.

However, the working speed is slow, the equipment is expensive, and it presupposes manual operation by a skilled technician, making it unsuitable for mass production.

MIG (Metal Inert Gas) welding is a semi-automatic method where the wire is fed automatically. The welding speed is fast, and it can handle long, continuous welds. The stability of the welding conditions is high, contributing to labor savings. It is particularly suited for mass-produced items of medium to thick plates, such as building materials and automotive parts.

By using a modern MIG welder with a pulse function (e.g., WT-MIG225AL), it is also possible to handle thin sheets. However, one must be cautious of troubles arising from the softness of the aluminum wire and the difficulty of initial setting adjustments. The visual finish is somewhat rougher compared to TIG, but it has an overwhelming advantage in terms of welding speed.

In recent years, high-precision, high-output welding technology using laser light has been gaining attention. In particular, welding using fiber lasers creates an extremely small heat-affected zone, suppressing the risk of thermal distortion and burn-through. It enables stable joining even on thin sheets, and the bead width is very narrow, resulting in excellent aesthetics.

Specifically, it is being put to practical use in the joining of electronic device casings and precision parts, as well as in medical equipment and aircraft components. However, the initial investment in equipment is high, and regular maintenance of the optical system and safety measures are also necessary, so its introduction requires a certain scale and specific applications.

Aluminum may seem like a simple material at first glance, but in reality, many types exist, each requiring the selection of an appropriate welding method and filler material (welding rod). Here, we will organize the types of representative aluminum materials, how to choose the right welding rod, and specific precautions for castings.

The composition and properties of aluminum materials vary greatly depending on their grade.

Selecting the appropriate welding rod for these materials is the key to safe, high-quality welding.

Commonly used aluminum filler materials include “4043” and “5356.”

A4043 (Al-Si series) contains about 5.0% Si, has high fluidity, and is resistant to cracking, making it ideal for castings and the 6000 series.

A5356 (Al-Mg series) contains 4.5-5.5% Mg and excels in tensile strength and corrosion resistance, so it is used for structural members of the 5000 series.

Also, the melting point of 4043 is about 573-582°C, while 5356 is 588-649°C, and this difference in the temperature at which they start to melt is another factor in selection.

In aluminum welding, cast and rolled materials have vastly different properties, so the construction methods must also be adapted.

The following measures are effective when welding castings:

With these工夫 (innovations/adjustments), it becomes possible to handle the difficult welding of castings.

In aluminum welding, defects are prone to occur depending on the properties of the base material and the welding conditions. Therefore, it is extremely important to correctly understand the necessary preparations and precautions during welding. Here, we will organize four points that require special attention on-site.

Aluminum has high thermal conductivity and a low melting point, so in the case of thin sheets, heat diffuses quickly, making them susceptible to burn-through or deformation. If the torch is moved at a constant speed, the molten pool can become too large, widening the bead or creating a hole.

The following countermeasures are effective:

In the case of thin sheets, the technician’s experience and ability to make visual adjustments are particularly tested.

Since aluminum often has an oxide film or anodized treatment on its surface, pre-weld surface treatment is essential. Especially when using materials for DIY purposes or second-hand parts, it can be difficult to judge by appearance, so the following preparations are necessary:

Also, when choosing a TIG welder, being “AC (alternating current) mode compatible” is an essential condition.

In recent years, TIG welders with a “pulse function” have become mainstream. This is a mechanism that alternates between high and low currents to balance penetration and solidification, achieving a beautiful bead and stability.

The main benefits of the pulse function are as follows:

Additionally, in AC mode, the polarity of the base material and the electrode alternates, providing a “cleaning effect” that stabilizes the arc while automatically removing the oxide film.

Although there is little spatter in aluminum welding, strong arc light, heat, and harmful gases are generated, so the following protective equipment is essential:

Especially for long hours of work or semi-automatic welding, it is advisable to prepare leather sleeves that protect up to the arms and a heat-resistant apron for added safety.

Aluminum welding is not a straightforward task, but by learning from both success and failure stories, you can avoid mistakes on-site and achieve more reliable processing. Here are three representative examples.

An auto repair shop repaired a crack in an aluminum wheel of a vehicle used for drift competitions in-house. The base material was cast aluminum with a thickness of about 6mm. They used a TIG welder and a 4043 welding rod. Before welding, they carefully removed the oxide film with a grinder and performed the welding while shielding with argon gas. The bead was left as is for the finish, and grinding treatment was intentionally not performed.

As a result, no recurring cracks occurred in the welded area, and it was able to withstand the intense vibrations during competition. The selection of the appropriate material and a “finish without over-grinding” are cited as the factors for success.

A DIY user trying to weld a motorcycle engine cover (aluminum casting) encountered a phenomenon where bubbles suddenly frothed up from the base material during welding. This was because “porosity,” which are microscopic voids inside the casting, contained oil and moisture, which evaporated all at once due to the arc heat.

In such cases, measures such as thoroughly heating the base material with a torch before welding to evaporate the oil, or grinding deeply from the surface to expose a “sound metal layer,” are effective. This case shows that the outcome of welding castings is greatly influenced by whether pre-weld heating and cleaning are performed.

A user who repaired a crack in an aluminum motorcycle frame with TIG welding later ground the bead flat with a grinder for post-processing, only to have the same spot fracture a few weeks later.

This was caused by “residual stress concentration” due to grinding away the tensile stress distribution effect that the weld bead provides. Especially in areas subjected to vibration or load, the shape of the bead itself plays a role in supporting the structural strength, offering the lesson that aesthetic appearance and strength are often a trade-off.

A: For small parts and repair-level work, DIY with a TIG welder is entirely possible. However, this is on the premise that the base material (grade), oxide film removal, and welding rod selection are all appropriate. Since an AC-compatible TIG welder and argon gas are required, the initial investment is considerable. If you want to work stably, a thickness range of about 1-3mm is a good guideline.

A: Most aluminum materials sold at home improvement stores have an anodized (anodic oxide film) coating on the surface. This film obstructs electrical current and significantly degrades weldability, so it must be physically removed with a grinder or similar tool. Also, the material grade is often not specified, making it difficult to know the compatibility with the welding rod, which is another challenge for DIY.

A: TIG welding is performed with manual control, so the bead (weld line) tends to be beautiful and uniform, with little spatter. It is particularly suitable for products where appearance is important or a fine finish is required. On the other hand, semi-automatic (MIG) welding excels in speed and productivity, but the bead tends to be slightly thicker and some spatter occurs, so the finish is more practical. The choice depends on the application and the importance of aesthetics.

In this article, we have organized practical knowledge about aluminum welding, covering its technical characteristics, selection of welding methods, choice of filler materials, and even success and failure stories that can occur on-site.

While aluminum is excellent in processability, it is a material that requires a high degree of caution in welding due to the effects of oxidation and thermal conductivity. With the right knowledge and preparation, it becomes possible to properly use various methods such as TIG, MIG, and laser.

For engineers, the ability to judge the optimal welding conditions according to the application and material is required. For procurement managers, material selection and the evaluation of the technical capabilities of subcontractors are directly linked to achieving both quality and cost.

As the demand for aluminum continues to grow, “how to handle weldable aluminum materials” will become a crucial theme that determines the success or failure of design and processing.

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