21.2 Welding Aluminum
David Colameco, M.Ed.
Development of welding aluminum
Aluminum has been an important material throughout the industrial age of the United States. The first method to be used to weld aluminum was oxy-acetylene as shown in Figure 21.2 below. Today GMAW and GTAW are used. GTAW can be used to weld aluminum using DCEN, DCEP, and AC. However, AC accounts for the vast majority of GTAW welding. In rare circumstances you may find DC still being used. Modern GTAW machines have complex electronics that help produce a waveform that provides the proper balance of cleaning action (Electrode Positive) and penetration (Electrode Negative).
GTAW of aluminum was used during World War II for airplanes and this process is still used today to weld aluminum. Originally GTAW was used with large electrodes running DC electrode positive (DCEP). This allowed for minimal penetration of the thin aircraft aluminum, with great cleaning action, but the electrodes had to be larger to account for the increased heat going into the electrode with DCEP vs DCEN. Figure 21.3 shows a modern welder working on a large piece of aluminum tooling using GTAW with most likely AC.
If GTAW works best when welding with AC wouldn’t you weld GMAW using AC also? According to an article by The Fabricator, AC GMAW machines for Aluminum have been in existence for decades, however their cost can be too high compared to their benefit as compared with DC GMAW machines (Armao, 2016). Most likely you will find your welding school and future employer will be using GMAW DCEP for welding aluminum because the machines they purchase can be used for multiple purposes. DCEP in GMAW is ok because we want to melt the GMAW wire. If you work in a shop that does a lot of aluminum welding, you would be more likely to find an AC GMAW machine. No matter what, if you are going to weld aluminum in your career it is highly recommended to learn both GTAW and GMAW preferably on aluminum but if aluminum is not available other materials are better than no experience because your future employer will train you on the differences of aluminum welding.
Basics of welding aluminum
Aluminum starts to form an oxide layer immediately after a new surface of the metal is exposed to the atmosphere, such as after it has been cleaned or sheared. The complete oxide layer takes more than days to form but if you take a break, of any length of time where you are not immediately welding, after cleaning your aluminum base material prior to welding, you will need to clean the material once you return. When cleaning aluminum use only stainless steel wire brushes and other tools that are only used with aluminum. When wire brushing, only brush in one direction to prevent embedding aluminum oxide and other impurities into the softer metal than steel is.
Not all aluminum alloys are weldable. Table 21.1 makes broad generalizations about the weldability of aluminum alloys but there are always exceptions to the rules. The aluminum alloys that are not easy to weld take more skill and strict adherence to welding procedures or recommended settings. The 8000 alloy series of aluminum is a mix of cats and dogs when it comes to alloy constituents that makes it not possible to categorize the series in the table..
|
General Weldability |
Alloy Series |
|---|---|
|
Easily Weldable |
1000, 3000, 5000, and some 4000 |
|
Can be welded with higher heat and speed |
2000, 6000, 7000, and some 4000 |
Note. Aluminum Alloys from Steelworker, Volume 1, NAVEDTRA 14250 by NETPDC, (p. 8-13), 1996, U.S. Navy.
The following gas mixtures may be used when welding aluminum. Additional gasses and mixtures are likely available that replace the more expensive helium.
|
NAVEDTRA 14250 |
Shielding Gas % |
Welding Process |
||||||
|---|---|---|---|---|---|---|---|---|
|
Metals |
Argon |
Helium |
CO2 |
O2 |
H2 |
GTAW |
GMAW |
Polarity |
|
Aluminum |
100 |
X |
DCEP |
|||||
|
100 |
X |
AC |
||||||
|
100 |
X |
DCEN |
||||||
|
25 |
75 |
X |
||||||
|
Mild Steel |
100 |
X |
DCEN |
|||||
|
75 |
25 |
X |
DCEP |
|||||
|
100 |
X |
|||||||
|
100 |
X |
|||||||
|
98 |
2 |
X |
||||||
|
Low Alloy |
97 |
3 |
X |
DCEP |
||||
|
95 |
5 |
X |
||||||
|
80 |
20 |
|||||||
|
80 |
20 |
|||||||
|
Stainless |
99 |
1 |
X |
DCEP |
||||
|
95 |
5 |
X |
DCEN |
|||||
|
80 |
20 |
X |
||||||
|
100 |
X |
|||||||
|
100 |
X |
|||||||
|
Titanium |
100 |
X |
DCEN |
|||||
|
100 |
X |
|||||||
|
100 |
X |
Note. “X” denotes a common/preferred combination
Parameters and gas mixtures can be found on your WPS or the filler metal manufacturer’s recommendations. Figure 21.3 shows a welder posing for a picture with a GTAW torch and aluminum base material.
It should be noted that SMAW Aluminum electrodes do exist but are not approved for code welding. Welding aluminum with SMAW should be done in emergency situations only to get a weldment back to a repair shop where the temporary welds can be replaced with GMAW or GTAW. For example, if a friend’s aluminum trailer cracked, you could use SMAW to temporarily repair the trailer so it can be driven empty to a shop to repair it.
The reason SMAW is not approved for code welding is because it is not reliable enough. The process is prone to porosity and flux inclusions that promote internal corrosion. Similarly, FCAW and SAW have not had fluxes developed for commercial use and are not used for welding aluminum.
Repair shops and home welders successfully use SMAW on aluminum however they may use special waveforms, techniques, and experience to ensure welds that meet their requirements. If you are not working with an experienced SMAW aluminum welder, it is recommended that you use GMAW or GTAW for home and hobby use to ensure a higher quality weld.
Uses of aluminum in industry today
Aluminum is used as a lightweight alternative to steel due to its high strength to weight ratio. Aluminum is used by a variety of industries as noted in Table 21.3. It has the added benefit of being 100% recyclable.
|
Aluminum Alloy Series |
Primary Alloying Elements |
Industry Uses |
|---|---|---|
|
1000 |
99%+ Pure Aluminum |
Electrical and Chemical |
|
2000 |
Copper |
Aerospace Industry |
|
3000 |
Manganese |
Sheet products, cans |
|
4000 |
Silicon |
Welding Filler Material |
|
5000 |
Magnesium |
Aerospace, Automotive |
|
6000 |
Silicon and Magnesium |
Aerospace, Trucking, Plate |
|
7000 |
Zinc |
Aerospace Industry |
|
8000 |
Miscellaneous |
Miscellaneous |
Note. Aluminum Wrought Alloy from Operator’s Circular Welding Theory and Application: Reporting Errors and Recommending Improvements, TC 9-237 by U.S. Army (p. 7-66), 1993.
As a welder in Washington State, you will most likely encounter aluminum in the trucking industry, marine industry, and the aerospace industry. Figure 21.4 and Figure 21.6 show trucking and marine uses.
Aluminum is also used in sheet form in some car doors as shown in Figure 21.6. There is research in using friction stir welding for the automotive industry. Friction stir welding is beyond the scope of this text, however as an example of aluminum used in industry, these car doors and NASA applications are important to note. In Washington State aluminum is also used in the aerospace industry but it is riveted more than welded. This does not mean that it is not welded in the aerospace industry. Certain parts of the plane such as the engine or landing gear may be welded. Figure 21.8 below shows the base of the Orion Spacecraft made from aluminum by NASA.
Figure 21.8 shows an experimental setup on aluminum for Friction Stir Welding.
Attributions
- Figure 21.1: Production. A-31 (“Vengeance”) dive bombers. Aluminum welding. This woman worker at Vultee-Nashville is pictured doing aluminum welding operating on one of the parts for the Vultee “Vengeance” dive bomber. The “Vengeance” (A-31) was originally designed for the French. It was later adopted by the RAF (Royal Air Force) and still later by the U.S. Army Air Forces. It is a single-engine, low-wing plane, carrying a crew of two men and having six machine guns of varying calibers. by Alfred T. Palmer, U.S. Office of War Information; Library of Congress, Prints & Photographs Division, Farm Security Administration/Office of War Information Black-and-White Negatives in the Public Domain; United States government work. The contents of the Library of Congress Farm Security Administration/Office of War Information Black-and-White Negatives are in the public domain and are free to use and reuse.
- Figure 21.2: Welder Joel Chavez welds a tooling fixture. by Department of Energy, Y-12 National Security Complex in the Public Domain; United States government work.
- Figure 21.3: Welding Aluminum Industry Edited 2020 by Tool Dude8mm is released under CC BY 2.0
- Figure 21.4: Gravel Roads Construction and Maintenance Guide by U.S. Department of Transportation, Federal Highway Administration in the Public Domain; United States government work
- Figure 21.5: Boat EM1B1873 (47987858617) by Bengt Nyman from Vaxholm, Sweden is released under CC BY 2.0
- Figure 21.6: Project 366 #172: 200620 Behind The Door by Pete is released under CC BY 2.0
- Figure 21.7: Michoud Assembly Facility. Pieces for the Orion spacecraft that will fly on Exploration Mission 1 are being prepared for welding at the Michoud Assembly Facility in New Orleans, Louisiana. by NASA Orion Spacecraft is released under CC BY-NC-ND 2.0
- Figure 21.8: Friction stir processing © Andrea Starr, Pacific Northwest National Laboratory Used with permission. Courtesy of Pacific Northwest National Laboratory, U.S. Dept. of Energy.