From Selection to Storage: The Basics of Common Aluminum Filler Metals

In order to gain the best results when welding aluminum, here are the reasons why and how it is critical to select the correct filler metal and carefully follow the proper storage and handling procedures for these products.

Due to its strength, corrosion resistance and versatility, aluminum has become an increasingly popular material in industries ranging from aerospace to trailer fabrication and shipbuilding.

In order to gain the best results when welding this material, it is critical to select the correct filler metal, and carefully follow the proper storage and handling procedures for these products. That rule stands whether you are using the gas metal arc welding (GMAW) process, which utilizes welding wires, or the gas tungsten arc welding (GTAW) process, which requires cut-lengths (often call filler rods).

MAKING THE FILLER METAL SELECTION
As a general rule, 4043 and 5356 aluminum filler metals are the least expensive, the most readily available and also the most appropriate choice for over 85 percent of aluminum applications. Deciding between the two depends on the answer to five key questions:
(1) What is the aluminum base designation?
(2) Will the welded component be exposed to sustained elevated temperature?
(3) Will the weldment be subjected to post-weld anodizing?
(4) Will shear strength, ductility and toughness be a prime consideration?
(5) Will post-weld heat treatment be performed?

After answering these questions, it’s relatively easy to decide between a 4043 or a 5356 aluminum filler metal.

4043 ALUMINUM FILLER METALS: APPLICATIONS AND CHARACTERISTICS
If you are welding 5XXX or 6XXX series aluminum that contains less than 2.5 percent magnesium, a 4043 filler metal is an appropriate selection. It also works well for applications that will be subject to long-term elevated temperature exposure (above 150 deg F). A 4043 filler metal is also appropriate for the following:

• Reducing distortion on aluminum applications
• Gaining brighter welds
• Reducing the opportunity for termination and shrinkage cracking

A 4043 filler metal also is usable for higher shear strength applications, but it takes approximately three fillet passes with this alloy to equal the shear strength of one pass using a 5356 filler metal.

Like any filler metal, the characteristics of a 4043 product are distinct. These filler metals create welds with smooth surfaces and have a relatively fluid weld pool due to the addition of 5 percent silicon. In order to control that fluidity, it is important to weld at higher voltages when using a 4043 filler metal. Consult the data sheets for the recommended operating parameters for the product you have selected.

A 4043 filler metal operates using 100 percent argon shielding gas, which provides good arc initiation and stability. In some cases, however, you may consider adding helium to the mixture. Helium is a hotter gas and the addition of it to a shielding gas mixture provides for better penetration, particularly on thicker aluminum. Helium, though, is quite expensive and does not provide as good arc stability as argon.

5356 ALUMINUM FILLER METALS: APPLICATIONS AND CHARACTERISTICS
A 5356 filler metal can be used to weld 5XXX series aluminum containing more than 2.5 percent magnesium, and like a 4043 filler metal, it can also be used to weld 5XXX or 6XXX series aluminum that contains less than 2.5 percent magnesium. Also consider this filler metal for:

• Achieving good anodized color matching
• For applications requiring higher ductility and toughness (such as those subject to dynamic loading)
• For applications requiring higher shear strength

The operating characteristics of a 5356 filler metal are different from a 4043 product. These filler metals contain 5 percent magnesium and produce a rippled weld, but they also create a layer of smut that requires cleaning after the weld has been completed. Like a 4043 product, these filler metals operate using 100 percent argon shielding gas and can also be used with the addition of helium.

Aluminum wires with a 5356 designation operate at lower voltages and with higher wire feed speeds than 4043 filler metals, allowing for greater penetration and better fusion at the throat of the weld. Again, consult the data sheet for specific operating parameters.

PROPER STORAGE AND HANDLING
Regardless of whether you use 4043 or 5356 alloys, it is important to keep the filler metals in a clean, dry area that is of a similar ambient temperature as the weld cell. Moving them from a cold area to one of room temperature causes condensation on the surface of the filler metals and can lead to poor weld quality.

After a shift, keep the filler metals in the weld cell so they can remain at the same temperature at which you will use them next. If using the GMAW process, cover the spool with the plastic bag the wire shipped in or with another protective cover. You can keep GTAW cut-lengths in their original box to protect against dirt and debris.

When handling the 4043 and 5356 alloys, remember to wear gloves to protect the filler metals against any moisture or oils on your hands.