Page 38 - MetalForming April 2020

FABRICATION
Aluminum Welding:
Getting to the Basics
From understanding potential pitfalls to following best practices for pre-cleaning, equipment setup and more, each contributes to higher- quality welds and supports good productivity.
BY ALVIN KIRKSEY
Manufacturers specify alu- minum alloys for their high strength-to-weight ratio and corrosion resistance, which makes them an attractive choice in industries such as transportation, automotive and aerospace, as well as for general man- ufacturing and fabrication. Aluminum alloys afford the opportunity to reduce the weight of completed parts without sacrificing durability, and stamped and fabricated aluminum parts can better withstand extreme service conditions compared to many other materials.
Aluminum’s high thermal conduc- tivity adds to its appeal. It can be used for applications such as radiators and heat exchangers, and at a lower cost than copper, for example.
When welding aluminum, metal for- mers must understand the basics to obtain optimum results. From under- standing potential pitfalls to following
Alvin Kirksey is a welding engineer with Hobart Filler Metals, Troy, OH: www.hobartbrothers.com.
Skilled welders employ specific techniques on aluminum. When welding with solid alu- minum wire, they use a push angle that creates a wide weld bead and good tie-in at the toes of the weld.
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best practices for pre-cleaning, equip- ment setup and more, each contributes to higher-quality welds and supports good productivity. Knowing the basics also can help prevent costly downtime for rework.
The Challenges
Due to its high thermal conductivity, aluminum requires welding at relatively high amperage, which increases the potential for burnthrough on thinner sections. This characteristic also makes aluminum prone to incomplete fusion at the start of welds, since the rest of the base material pulls away the heat so quickly, and makes crater fill difficult at the end of welds. Welding power supplies with adaptive features will help prevent these two issues. Other suggestions: Travel slowly at the begin- ning of each weld, and increase the
contact tip-to-work distance at the end of each weld.
Porosity also challenges welders working with aluminum, and can result from improper base-material prepa- ration; the presence of contaminants (dirt, oil, grease or paint); filler metals exposed to moisture; loose gas con- nections; and shielding-gas contami- nation. The presence of hydrogen in the weld pool—from the filler metal and the aluminum itself—also can lead to porosity. Hydrogen is very soluble in aluminum and easily can become trapped as the weld solidifies.
Hot cracking also can arise during aluminum welding, and results from chemistry as opposed to mechanical stresses. Certain aluminum alloys, such as 6000-series grades, are more sus- ceptible to hot cracking than others. The filler metal used also affects the