Automotive Industry Trends
April 2003
Welding aluminum: different, not difficult
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If you’ve ever heard welding expert Tony Anderson talk about welding aluminum at an American Welding Society (AWS) show, or if you’ve read one of Anderson’s many articles in Welding Journal, chances are you’ve heard Anderson say, “Welding aluminum isn’t difficult. It’s just different.”
He should know. Anderson is chairman of the Aluminum Association’s (AA) Technical Advisory Committee on Welding and Joining, as well as chairman of two American Welding Society (ASW) committees and vice chairman of a third. He’s also Technical Services manager for AlcoTec Wire Corporation. Following is a look at a few welding factors Anderson urges engineers to consider when designing cars and other products with aluminum components.
Softness affects wire-feeding process
Anderson identifies wire-feeding as the most likely problem to arise when gas metal-arc (GMA) welding of aluminum versus steel. That’s because aluminum is softer than steel.
“Steel welding wire is rigged, it can be fed more easily over a greater distance, and can withstand more mechanical abuse when compared with aluminum,” explains Anderson. Because aluminum is susceptible to deformation or shaving during the feeding operation, Anderson recommends:
- Watching wire quality and diameter: High quality and consistency of the wire minimizes issues with the wire-feeding process, as does wire thickness. Thinner wires may lead to irregular wire feed or “burn-backs” in which the welding wire fuses to the inside of the contact tip.
- Matching feeding distance with feeding systems: “For aluminum feeding, there are four recognized feeding systems used: push feeders, pull feeders, push-pull feeders, and spool on gun systems,” says Anderson, who recommends limiting feeding distance to 12 feet with push or pull feeders. He adds, “Push-pull feeders were developed to overcome the wire feeding problems experienced by other systems.” For smaller, light-duty applications, Anderson says the spool-on-gun system might work well.
- Choosing the right contact tip: “You should only use contact tips made specifically for aluminum wire welding,” Anderson notes. He also advises looking for smooth internal bores and avoiding sharp burrs on the ends of the tips that could shave soft aluminum alloys.
Hydrogen could lead to porosity
Porosity is the presences of gas pockets or inclusions in a weld, and aluminum can be susceptible to excessive porosity because in molten aluminum, hydrogen gas is highly soluble.
Hydrogen’s presence and contamination of the welding may stem from moisture introduced through a variety of sources. These include moisture soaked up by aluminum’s naturally occurring oxide layer. “The aluminum oxide layer is porous and can absorb moisture, grow in thickness and become a major problem when attempting to produce welds that are relatively porosity free,” says Anderson. Correct storing of the aluminum can minimize this risk.
Another possible source of hydrogen contamination resides in paint, lubricants and other hydrocarbon materials often found in manufacturing environments. “When designing welding procedures intended to produce low levels of porosity, it is important to incorporate degreasing and oxide removal,” Anderson says.
Anderson also identifies hot cracking as a potential problem area of welding aluminum. To learn more about his and other issues, check out Anderson’s technical papers* available on the AlcoTec web site. There, you’ll find a detailed discussion of wire-feeding and porosity issues noted above, as well as a look at factors leading to cracking and a thoughtful discussion on alloy content versus crack sensitivity. 3
3 Technical papers written by Tony Anderson and used for reference and quotation purposes in this story can be found at http://www.alcotec.com under the heading, Online Technical Information for Aluminum Welding.