Aluminum in Welding Operations: Characteristics, Alloys, and Series
Compared to other materials used in welding operations, aluminum has distinct characteristics that necessitate special handling procedures and bring about unique challenges. The properties of aluminum and its various alloys influence how well the material takes to the welding process and the performance of the end product. For example:
- It has a much lower melting point than steel (1,222 degrees Fahrenheit compared to 2,500 degrees Fahrenheit). This quality allows for welding operations to occur at lower temperatures to achieve a comparable weld.
- It has an oxide layer with a melting point of 3,700 degrees Fahrenheit that acts as an insulator, which may cause issues during lower temperature welding operations.
- It loses strength as it heats up and regains strength as it cools down. In contrast to steel, aluminum remains strong in colder temperatures, making it suitable for use in cryogenic and liquid natural gas (LNG) transportation applications.
Most, if not all, aluminum alloys demonstrate these properties as they are comprised of mainly aluminum with smaller percentages of other elements. The following list outlines the series classifications of aluminum and their corresponding alloy elements:
- 1xxx series (pure aluminum) – No elements added intentionally
- 2xxx series (heat-treatable) – Copper
- 3xxx series (non-heat-treatable) – Manganese
- 4xxx series (non-heat-treatable) – Silicon
- 5xxx series (non-heat-treatable) – Magnesium
- 6xxx series (heat-treatable) – Magnesium and silicon
- 7xxx series (heat-treatable) – Zinc
- 8xxx series – Other elements
Aluminum Welding Considerations
When planning an aluminum welding project, there are several factors to keep in mind to ensure the best possible weld. Three of the key considerations are:
Cleanliness of the Aluminum Surface
Any contaminants on the surface of the aluminum workpiece can interfere with the welding process. In addition to potentially altering the chemical reaction that occurs during welding operations, they can weaken the strength of the weld. In particular, aluminum’s tendency to attract and react with oxygen—forming a thin oxide layer on the surface—necessitates thorough cleaning and preparation of the aluminum surface before the commencement of any welding operation.
Size of the Aluminum Workpiece
Aluminum sheets and plates are available in a variety of thicknesses to suit a wide range of applications. Depending on the thickness of the workpiece employed in a welding operation, some welding techniques may not be appropriate while others may be ideal. For example:
- Butt and fillet welds are generally not suitable for joining aluminum plates less than 1/8 inch (3/2 mm).
- Metal arc welding is suitable for heavier aluminum materials that are up to 2 1/2 inches (63.5 mm) thick.
Thermal Conductivity of Aluminum
Aluminum has a relatively low melting point for metal. This quality, combined with a high degree of thermal conductivity, requires a careful balance of heat application to avoid both premature heat dissipation and melting. Aluminum conducts heat between three to five times as fast as steel does, and each of its alloys has a slightly different level of heat conductivity.
To account for these factors, welding technicians tend to use higher heat inputs to allow for faster welding speeds and preheat thicker pieces of aluminum before executing any welding operation. During the preheating process, technicians heat the aluminum to no more than 400 degrees Fahrenheit to curtail the variability caused by the conductivity. However, as exposure to too high heat for too long can reduce the weld strength in heat-treated and work-hardened aluminum alloys, the workpiece is heated for the smallest amount of time possible.
Aluminum Welding Techniques
With these considerations in mind, industry professionals can choose the best techniques for different aluminum materials, part sizes, and intended applications. The most common aluminum welding techniques include the following:
Gas Metal Arc Welding (GMAW)
Gas metal arc welding (GMAW)—also known as metal inert gas (MIG) welding—uses inert gas and direct current reverse polarity to weld two pieces of aluminum together. It is suitable for welding aluminum plates ranging in thickness from 1/16 inch to several inches. As a welding technique, it is quick and versatile, offering fast welding speeds for a wide range of materials and intended applications.
Gas Tungsten Arc Welding (GTAW)
Gas tungsten arc welding (GTAW) —also referred to as tungsten inert gas (TIG) welding—utilizes tungsten gas to create an arc. In contrast to GMAW, it is better suited for thinner aluminum plates or sections of aluminum alloys.
Shielded Carbon Arc Welding (SCAW)
Shielded carbon arc welding (SCAW) is a manual or automatic welding process that uses carbon gas to generate an arc. The carbon arc, combined with filler material from a separate filler rod, is used to complete the weld. Although flux is required throughout the duration of the welding operation, it must be removed at the end. End products produced in SCAW operations have welds identical to products made in oxyacetylene or oxyhydrogen welding operations.
Shielded Metal Arc Welding (SMAW)
In shielded metal arc welding (SMAW) operations, welders use an electrode coated with extruded or heavy dipped flux. This coating protects the weld by forming a gaseous shield around the arc and molten material. It also combines the aluminum oxide to create slag, which can be removed at the end of the welding process or during finishing operations.
Atomic Hydrogen Welding
Atomic hydrogen welding operations use an atmosphere of hydrogen gas to maintain an arc between two tungsten electrodes. The process, techniques, and results are similar to that of oxyacetylene welding, and manufacturers can automate the process or perform it by hand.
Stud welding uses conventional arc stud welding tools and a special welding gun adapter (which allows for control of high-purity shielding gases) to weld studs with diameters ranging between 3/16 and 3/4 inches. The process employs either capacitor discharge or drawn arc capacitor discharge techniques.
Electron Beam Welding
In electron beam welding operations, welding technicians bombard the aluminum pieces with a high-velocity stream of electrons. This stream fuses the joints together by transforming the kinetic energy of the electrons to heat energy upon contact with the workpiece(s). As this process can be hazardous, it generally takes place in an evacuated chamber.
There are three main resistance welding methods: flash welding, seam welding, and spot welding. Each of these processes is suitable for joining aluminum and aluminum alloys, including high-strength, heat-treatable aluminum alloys.
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At Miracle Welding, we have over 44 years of experience manufacturing and welding high-quality products. The knowledge and skills gained from this experience allow us significant insight into the nuances of aluminum welding operations, including how the alloys, part sizes, and techniques employed affect the quality of the welded end product.
From MIG and TIG to arc welding and resistance welding, we have the know-how to meet all of your aluminum welding needs. Contact our team today to learn more about our welding capabilities, or request a quote to discuss your next welding project specifications with one of our experts.