For many years, GNEE has worked exclusively with Alcotec aluminum welding wires because of their outstanding quality and consistency. Several D/F Machine Specialties torches are even used in the Alcotec laboratory, ranging from the Water-Cooled Pistol Gun commonly used by trailer manufacturers to the 1000-amp BIG MIG Machine Barrel designed for aluminum wires up to 1/4 inch in diameter.
A key difference between arc welding aluminum and steel lies in the method used to evaluate filler alloy selection. Numerous aluminum-based alloys can be successfully welded using multiple different filler materials. For example, the base material mentioned in the question-6061-T6-is commonly welded using at least four completely different filler alloys and can also be welded successfully with several others.
So how do we determine the most suitable filler alloy? The answer is that it is impossible to choose the best filler without first understanding the application, service conditions, and performance expectations of the welded component. When selecting an aluminum filler alloy, we must identify which weld-performance variables are most important for our situation. Using an unsuitable filler alloy can result in inadequate performance or even premature weld failure. Filler alloys used for arc welding aluminum are typically evaluated according to the following criteria:
Ease of Welding:
This refers to resistance to weld cracking. Hot cracking sensitivity curves for various aluminum alloys, combined with consideration of base and filler alloy dilution, help determine crack sensitivity ratings for each filler/base alloy combination.
Strength of the Weld Joint:
It is essential to consider the tensile strength of groove welds and shear strength of fillet welds when using different filler alloys. Even filler alloys that exceed the as-welded tensile strength of the base metal can differ significantly in shear strength.
Ductility:
This is important if the welded structure will undergo forming or if fatigue or shock loading is expected during service.
Corrosion Resistance:
This is a major consideration for components exposed to fresh or salt water.
Sustained Elevated Temperature Performance:
Some filler alloys behave poorly when exposed to temperatures above 150°F for long periods and may experience stress-corrosion cracking or early component failure.
Color Match After Anodizing:
For cosmetic applications, the color match between the base alloy and the filler after anodizing can be critical.
Post-Weld Heat Treatment:
A filler alloy's ability to respond to post-weld heat treatment depends on its chemistry and the joint design.
Application Examples
To illustrate the complexity of selecting the correct filler alloy, consider 6061-T6 used in several different applications:
1. 6061-T6 Tubing for Clear-Coat Anodized Handrails
In this situation, achieving a good color match after anodizing is the main priority. The most suitable filler is 5356, which produces a color closely matching the bright silver finish of the tubing. If fillers such as 4043, 4047, or 4643 were used, the weld would turn dark gray after anodizing and would not match the surrounding material.
2. 6061-T6 Angle Used as a Bracket for a Heating Component Operating at 250°F
Here, elevated-temperature performance is critical. Acceptable options include 5554, 4043, or 4047, as they perform well at higher temperatures.
Using 5356, 5183, or 5556-although commonly recommended for 6061-would risk magnesium sensitization, leading to stress-corrosion cracking and early failure.
3. 6061-T6 Used to Fabricate a Large Safety-Critical Lifting Device Requiring Post-Weld Heat Treatment
Most filler alloys typically used with 6061 will not respond well to post-weld solution heat treatment and artificial aging. Non-heat-treatable fillers such as 5356, 5183, and 5556 can experience undesirable changes.
The commonly used filler 4043 also does not respond to heat treatment unless highly diluted by the base metal.
For this application, 4643 is the best choice because it is heat-treatable and capable of achieving strength comparable to the base metal after post-weld heat treatment.
Making the Right Selection
Each variable relevant to the specific application must be evaluated carefully to determine the most suitable filler alloy. Fortunately, aluminum filler alloy selection charts are available to guide users, rating different fillers across all major performance criteria. When in doubt, it is best to consult experienced professionals.
As a supplier, GNEE recommends assessing all weld performance requirements to ensure the correct filler alloy is selected for optimal results.
