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Aluminum Welding: The Ultimate Guide to Perfect Welds
Aluminum is undeniably beneficial for engineering applications such as aviation, automotive, and sheet metal fabrication.
Like any metal in such applications, weldability is crucial for widespread use. Welding aluminum is a challenging skill that requires knowledge and practice to master.
This article will explore the process of welding aluminum, the different methods of aluminum welding, and the best practices recommended by industry experts.
Challenges of Welding Aluminum
Welding aluminum is a complex process that demands knowledge, skill, and experience. To achieve successful welding joints, it is essential to understand the various welding processes suitable for aluminum and the challenges and workarounds associated with those methods.
Thermal Conductivity
Combining these properties makes heat conduction through aluminum very efficient yet challenging to control. Potential issues such as part distortion, cracks, and burn-through are highly likely due to these properties.
Aluminum Oxide Layer
Aluminum quickly oxidizes when air is exposed, creating a thin oxide layer with a higher melting temperature (2072°C) than aluminum (660°C). Welding through this barrier may burn holes in the workpiece.
Before welding the workpiece, the oxide layer can be dissolved using solvents or acids. It can also be physically removed through mechanical abrasive techniques, such as using a stainless steel wire brush or sandblasting.
Impurities
Aluminum is susceptible and can easily become contaminated by dirt, air, and water during welding. Contamination can occur due to poor shielding or excessively long arcs which allow air to reach the weld. It can reduce aluminum’s strength and ductility and the formation of oxide on the welds, affecting appearance and complicating multipass welding. Hydrogen can also contribute to contamination, stemming from sources such as moisture in electrode fluxes, humid air, and damp weld joints. Therefore, it is crucial to thoroughly clean and store aluminum correctly before welding.
Thickness
When working with aluminum, welding materials of different thicknesses can be challenging. Welding thin and thick materials together can be challenging because the heat applied to the workpiece may melt through the thin material to create a strong weld joint.
To effectively weld different thicknesses of aluminum sheets, it is essential to have a deep understanding of aluminum grades, welding methods, and techniques. Welders can achieve successful results by adjusting parameters such as amperage and heat input to the optimal levels.
No Color Change
Most metals change color before melting, but aluminum is an exception. As a result, an aluminum welder lacks an indication of when the metal is about to melt.
Hot Cracking
High thermal stress can cause hot cracking in aluminum welds, making aluminum unsuitable for arc welding. Alloying elements and treatment can improve mechanical properties. Heat-treatable aluminum alloys include the (Al-Cu) 2xxx and (Al-Zn) 7xxx series.
6 Techniques For How To Weld Aluminum
Several welding processes are used for aluminum, each with its strengths and weaknesses. Welders typically opt for TIG and MIG welding, although other methods can be used to achieve specific and desirable results.
1. Gas Tungsten Arc Welding (TIG)
The preferred method for welding aluminum is TIG welding. This method gives the welder the most control, allowing them to regulate heat input, weld through the oxide layer, and manage the weld pool to prevent warping from excessive temperatures.
TIG welding with high-frequency AC is ideal due to its low contamination levels. The tungsten electrode does not need to touch the workpiece, reducing the risk of deposits in the weld pool.
However, TIG welding is slower and more costly due to the high skill requirement and expensive setup.
2. Metal Inert Gas Welding (MIG)
The second option for professionals is aluminum MIG welding. It is suitable for aluminum welding applications because of its ease of use, low cost, and wide availability. The bead quality is lower than TIG, but the results are promising.
It allows for better welding process control and is faster than TIG welding. Adjusting process parameters such as travel speed and part preheating can solve common aluminum welding issues like high thermal conductivity.
The softness of the aluminum wire can pose a problem.To avoid this issue, a spool or push/pull gun is required. Aluminum MIG welding necessitates 100% pure argon gas, which is inexpensive but generally unavailable in workshops due to its limited use.
Despite these limitations, MIG welding remains one of the best processes for welding aluminum.
3. Electron Beam Welding
Electron beam welding is an exact and effective method for welding aluminum. It directs a concentrated beam of high-velocity electrons to the joint interface, creating a high-temperature localized zone to achieve the weld.
One advantage of electron beam welding is its accuracy and cleanliness. It applies heat selectively to the exact desired location, minimizing the heat-affected zone and related defects. Additionally, the electron beam operates very quickly (approximately ten times faster than TIG or MIG welding), preventing excess heat from entering the material.
Furthermore, electron beam welding ensures high joint purity because the process occurs in a vacuum, removing most impurities from the welding zone during preparation. Additionally, the electron beam can penetrate as deep as 15 cm into aluminum, allowing for welding capabilities beyond just sheet metal.
However, electron beam welding has drawbacks, including high costs and skill requirements. Additionally, due to the restricted chamber size of the machines, part size is limited, which can be problematic when dealing with long aluminum extrusions.
4. Laser Welding
Laser welding is a rapid process focusing a high-power density beam on the aluminum surface. It enables precise welding of narrow widths and large weld depths, producing clean weld zones using shielding gas. 6xxx aluminum alloys are generally suitable for laser welding and are commonly used with a 4032 or 4047 aluminum-grade filler rod.
5. Resistance Welding
Resistance welding aluminum involves applying pressure and current to achieve fusion. Spot and seam welding are often used to join aluminum sheets. One challenge of this technique is dealing with high thermal and electrical conductivity.
6. Friction Stir Welding
Its innovative aluminum welding method is quickly gaining popularity due to its high potential. It uses a rotary tool to generate heat at the joint interface through friction.
One of its key advantages is that it is a solid-phase process that fuses materials below their melting point. As a result, heat-related issues are nearly eliminated. The heat-affected zone is minimal; there is no opportunity for contaminants to enter the joint as it never reaches a molten state, and there is minimal warping.
Additionally, friction stir welding is repeatable and cost-effective. However, it is still an evolving technology that will require time to reach its full potential.
How To Prepare For Aluminum Welding?
As mentioned at the outset, aluminum welding poses a challenge. Overcoming this challenge requires skill and experience. This section will discuss some precautions and preparation tips for aluminum welders that can help improve their learning curve.
Safety and Preparation
Any welding method requires protective gear (goggles, helmets, gloves, etc.). Knowing and understanding how the project will be executed beforehand is important to properly prepare for the welding process. Some preparation steps may include removing the metal’s oxide layer using chemicals or a steel brush and ensuring the equipment is clean.
Appropriate Welding Method
The standard aluminum welding methods have been discussed above. While there are only a few options, deciding on the most suitable technique is essential.
Typically, the choice comes down to TIG or MIG. TIG is the preferred method but requires a skilled aluminum welder and time. Additionally, it would be best to have a dedicated TIG welder in the shop. In most cases, aluminum welders opt for MIG for its ease of use and adequate quality in general applications.
Selecting the Correct Filler
The choice of filler material is crucial in determining the strength of a weld. Selecting the most suitable wire for your aluminum welding project is essential to ensure its quality. The optimal choice depends on the welding method, aluminum grade, and desired properties.
The filler metal’s properties should closely match those of the base metal. The diameter of the wire impacts the amount of material that enters the weld pool, influencing factors like strength, leak resistance, and ductility.
The most commonly used aluminum fillers are 4043 and 5356. 4043 is more suitable for welds exposed to extreme temperatures, which are prone to cracking and require a clean appearance. On the other hand, 5356 is focused on providing strength, offering high tensile and shear strength.
Evaluate the Proper Inert Gas
MIG and TIG use inert gas to shield the weld pool from reactive environments. The gas composition influences the weld quality, so it’s an essential consideration during the preparation.
100% pure argon is the ideal choice for both welding processes. It’s cheap and readily available. However, some aluminum welders prefer to add 20-25% helium to the mix for higher welding speeds and arc voltages.
Benefits of Using Aluminum
Why Use Aluminum?
The use of aluminum as a structural material is relatively new. In the past, aluminum was considered a precious metal and was not widely used. It wasn’t until 1886 that aluminum became available commercially, thanks to the finding of the electrolytic method for getting pure aluminum from aluminum oxide. Since then, aluminum has been recognized for its unique qualities and used in various applications such as aircraft, passenger automobiles, trucks, railroad cars, cookware, and marine equipment.
Despite the challenges of working with aluminum, this material offers several key benefits:
1. Lightweight: Aluminum has a better strength-to-weight ratio than steel and remains strong rather than brittle at low temperatures, making it ideal for projects requiring strength without adding weight.
2. Electricity & Heat Conductivity: Aluminum conducts electricity and heat almost as well as copper.
3. Non-corrosive: While oxidation poses challenges during welding, aluminum’s non-corrosive nature makes it a beneficial material.
4. Recyclable: Aluminum is cost-efficient and recyclable, contributing to its increasing popularity.
5. Appearance: Aluminum effectively absorbs paint and sealant, making it a popular choice for its cosmetic qualities.
As aluminum welding becomes more popular, welders today must have the skills to work with this material. This often requires formal hands-on training, like the Welding Technology program offered at Universal Technical Institute (UTI). In this program, students learn standard welding techniques, including TIG and MIG welding, and gain expertise in welding positions used for plate, sheet metal, and pipe. The program is developed in conjunction with the industry-leading brand Lincoln Electric.
Post Welding Aluminum Considerations
Aluminum welding is an efficient process with the potential to yield near-net shapes, although additional steps may be necessary to achieve the final desired form.
Quality Checking
It is standard procedure to subject the weld to quality checks. This ensures that it meets the requirements and can endure the operating conditions for which it is designed. The most common checks involve visually inspecting for defects such as porosity, undercuts, and burn-through. Additionally, non-destructive testing (NDT) techniques like X-ray and die penetrants are utilized to assess the quality of the weld.
Heat Treatment
During welding, metals lose some of their material properties, such as strength. Additionally, their chemical composition can change due to contaminants and high temperatures. As a result, it is common to subject the weld joint to heat treatments to restore its strength and improve its quality. The specific type of heat treatment depends on the base metal, filler, and quality requirements.
Aging
Aging is a common heat treatment process applied after aluminum welding. To restore some of its original strength, the weld joint is kept at low temperatures (~200℃) for an extended period.
Surface Finishing
Post-process surface treatments are an effective method for eliminating welding after-effects such as discoloration and heat tint. These treatments can be carried out using mechanical methods such as brushing, polishing, or chemical/electrochemical methods. Additionally, surface treatments like painting or coating are commonly applied during the final stage to achieve the desired cosmetic finish.
Conclusion
Aluminum welding is a fundamental fabrication method in the manufacturing industry. It is suitable for joining different aluminum plates and thin sheet metal.
