ALUMINUM WORKSHOP
What determines aluminum filler strength?

I’m confused about various aluminum filler metal strengths. Does the filler designation tell me anything about the strength of the filler or the weld? I looked in AWS A5.10, the specification for aluminum GMAW and GTAW filler metals, and there are no strength requirements even in there. Why?

FRANK
ARMAO

The filler designation doesn’t tell you any-
thing about the strength of the filler or of
the weld. Aluminum fillers are different
from carbon steel fillers. Most carbon steels
have a fairly similar chemistry, so you pick
the filler that will give you a strength level in
the weld that is as strong as the carbon steel.
However, the chemistries of aluminum
alloys often are very different from each
other, and in most cases you can’t match the
strength level of the parent material in the
weld. Aluminum filler alloys are designed to
have chemistries that will have the lowest
crack sensitivity when used with a specific
aluminum material.

alloy you are welding. The applicable fabrication code will then tell you what the minimum required strength is for the base/filler combination you are using.

What determines the tensile strength of the filler wire and the weld? The biggest factor in determining weld strength is the chemistry of the base and filler metals. Of course, other factors come into play as well.

What determines the strength of the wire? Again, chemistry is a big factor, but the process of how the wire is drawn to size is a bigger factor. It starts as an annealed rod about 3⁄ 8 in. dia. and is drawn through a series of dies to reduce its diameter. Each drawing step cold-works the wire and makes it stronger. After a few dies, the wire is so strong and brittle that it will snap if it is drawn anymore. So it is annealed and then drawn again. This process is repeated until the wire reaches the desired diameter. At that point, the major factor determining the strength of the wire is how much cold-working it has received since the last annealing.

That’s why we don’t report the strength of filler wires—because you can get almost any value you want, within limits, by adjusting the drawing and annealing schedule. ■

Frank G. Armao is director, application engineering, North Asia, at The Lincoln Electric Co., 22801 St. Clair Ave., Cleveland, OH 44117, 216-481-8100, frank_armao@lincolnelectric.com, www.lincoln electric.com. He is a member of the AWS D1 Committee, chairman of the AWS D1 Aluminum Subcommittee, and vice chairman of the AWS D8G Automotive Aluminum Arc Welding Committee.