How to pick filler metal
No matter what welding process or materials are involved with your DIY welding projects and repairs, picking an appropriate filler metal for the job is crucial to creating a great weld.
Filler metal basics
DIY hobbyists weld a variety of materials. Depending on the application, they might need to fabricate or repair aluminum, mild steel, stainless steel or cast iron. No one filler metal will allow you to weld all materials, but there are a few options that should be in everyone’s arsenal.
Common filler metal options:
- Quantum Arc™ 6 (ER70S-6) is a good all-around filler metal for MIG welding relatively clean mild steel projects.
- Fabshield® 21B (E71T-11) is a good all-around self-shielded flux-cored wire that works well on steel projects when you have to weld outdoors and if you don’t have access to a bottle of shielding gas.
- Hobart® 447A (E6013) is a good all-around stick electrode for general purpose fabrication and repair of mild steel projects.
- Hobart MaxalMig® 4043 is a good all-around aluminum filler metal for welding aluminum.
Keep in mind that these filler metals come in many different sizes (diameters). Each filler metal size has a window in which it performs best. For example, if you are MIG welding mild steel with 0.024 ER70S-6 wire and you need to weld ¼-inch-thick material, 0.024 wire will not give good results. It will become harsh and high-spatter as the wire is exploding before melting in a controlled manner because the voltage to weld ¼-inch-thick material is too high for the 0.024 wire. The better option for that material thickness would be 0.035-size wire.
On the flip side, 0.035 wire would not weld light-gauge body panels well. The weld wire is larger than the base metal, and there’s an elevated chance of burning holes through the body panel because it takes more voltage to melt the 0.035 wire than the body panel can support.
As a rule of thumb, don’t use a filler metal that is thicker than the base metal being welded.
For DIY hobbyists, these are good general filler metal diameters to have on hand:
- 0.030 for MIG steel ER70S-6
- 0.035 for E71T-11
- 1/8-in. for your E6013 stick electrodes
- 0.035 4043 or 4943 for MIG welding aluminum with a spool gun
- 3/32-in. 4043 or 4943 for TIG welding aluminum
- 1/16-in. and 3/32-in. ER70S-2 TIG filler for steel
An excellent tool for determining weld settings and filler metal thickness is the Miller Weld Setting Calculator App.
Miller Weld Setting Calculator App
The Hobart Filler Metals app is another helpful resource available for Apple and Android devices. It has a step-by-step guide to selecting the right filler metal.
Hobart Filler Metals app for Apple
Hobart Filler Metals app for Android
There are many factors that play a role in choosing the right filler metal. For more in-depth filler metal selection, consider these six questions to fine-tune your filler metal needs.
6 Questions To Help Determine What Filler Metal To Use for DIY Welding
Q1: What is the base material?
The base material is the first and most important factor in determining the right filler metal. If you’re unsure what type of material you’re working with, do your best to find out what the metal is. The owner’s manual for whatever you’re repairing (if it’s equipment or machinery, for example) is a good place to start.
If you’re still unsure of what the base material is, there are some clues to look for that can help. If you know you’re working with aluminum but don’t know the specific type of aluminum — and the part is extruded, like a tube, pipe or channel — that design means the material is often a 6XXX series aluminum such as 6061 or 6063. The filler metal should be matched to the series of aluminum being welded. A fundamental difference between arc welding steel and aluminum is the evaluation method used during the filler alloy selection process. There are many aluminum base materials that can be welded successfully with any number of different filler alloys. The base alloy 6061-T6, for instance, is commonly welded with at least four different filler alloys and can be welded successfully with even more.
Aluminum typically requires a filler metal that is a different alloy than the base material. Steel and stainless steel typically require the filler to match the material. Most steels that are not put through harsh operations can often be welded with common mild steel fillers. Steels that are intended for more critical applications or experience harsh operations often require a more specialized filler metal. The temperature that the product will see is also a critical aspect that must be taken into consideration. Understanding filler metals to this depth can easily become overwhelming. You may want to reach out to your filler metal manufacturer for additional guidance.
Two other common materials seen in DIY projects are cast iron and cast steel. Cast iron contains some added elements that can make welding very difficult and even impossible in some cases. Cast steel, on the other hand, is less of a challenge because it is a more common steel that has been melted and solidified into a specific shape. Extensive research should be done when dealing with any casting, and proper research is even more critical to determine the correct alloy before welding. A good step in determining the part alloy is to talk with the manufacturer of the part or again, consult your filler metal manufacturer.
Q2: What is the service temperature?
Service temperatures at both extremes (hot and cold) should be taken into consideration when welding. Materials subject to long-term temperatures between freezing and the low 100s (Fahrenheit) typically don’t need a specialized filler metal, but it is a good idea to check the filler metal’s capabilities beforehand if this is a concern. These properties are listed on data sheets available for each filler metal product, typically found on the manufacturer’s website. For something like a handrail that isn’t under stress or subject to impact, extreme temperatures are less of a concern.
Q3: What is the required toughness?
Are strength, toughness and ductility the most important factors for the piece or part you’re welding? Or are aesthetics and how the finished part looks the most important? Different filler metal alloys provide different characteristics in the finished weld. Your filler metal choice will impact the toughness and strength of your weld, so be sure to choose a filler metal with the required toughness if that’s important for the finished piece and how it will be used. For instance, if you’re building a heavy-duty aluminum off-road trailer, select a filler metal with good strength/toughness, like 5356.
Just as with the familiar saying, “you are only as strong as your weakest link,” if your filler metal is weaker than your base material, then that will be the first thing to fail if the right conditions arise. This is called undermatching and is actually a common practice to reduce the risk of cracking. Undermatching the strength of the filler metal to the base material is often done in applications where the design of the weldment does not need to meet the strength of the base material. Often these welds are done on high-strength steel that will not experience heavy loads or impacts at the weld. Look to the American Welding Society (AWS) class of a filler metal to see the tensile strength of the material. An E71T-1 filler metal, for example, is a 70 ksi (70,000 psi) and an E111T1 is a 110 ksi (110,000 psi) product. Find the tensile strength of the base material and match it with a filler that fits your needs. There are factors other than tensile strength that must be considered, but that is a good starting point. Also, be aware that these types of steels (like a 4140 or HARDOX wear plate) often require heat treatment to avoid cracking or ruining other properties.
Q4: Does the weld require leak tightness?
With some welds, you need to ensure a complete seal so they don’t leak. In these cases, choose a filler metal that contains silicon if it is compatible with the base metal. For instance, if you are building an aluminum tank or repairing a pontoon, you might want to select a 4XXX filler metal that allows the weld to wet out and seal better. With steel it is common to mistakenly use the wrong gas or other aspects that could contribute to leaks. Refer to the data sheet to ensure you are following the correct procedures.
Q5: What material thickness are you welding?
The thickness of your base material will impact the size or diameter of the filler metal you need, but it does not typically affect the filler metal alloy. It is important to consider how the weld will be affected because of the thickness of the material. This will contribute to the level of stress in the steel and needs to be considered when welding, otherwise there is a risk of failure. Preheating the steel and keeping it at a specific temperature until all the welding is done (known as interpass temperature) helps to relieve these stresses and is more important the thicker the material gets. Some common filler metal products used for DIY welding actually have a thickness limitation like Fabshield 21B (less than 3/4-inch thick) and Fabshield 23 (less than 1/4-inch thick). Again, it is important to look over a data sheet whenever running a new product or experiencing difficulties.
Q6: Are you welding in the shop or outdoors?
If your project requires welding outside, you may have to deal with wind and the elements. In these situations, a self-shielded flux-cored wire or a stick electrode are typically better choices than TIG or MIG welding. Stick rods and self-shielded flux-cored wires don’t require a shielding gas. This makes them better suited for welding in windy outdoor conditions. Shops can sometimes get drafty as well if a bay door is open or a large fan is on. Gas-shielded products are not recommended to be used in environments where the wind speed will be 5 mph or greater.
Choosing filler metal for DIY welding projects
Not every filler metal fits every job, so it’s important to understand a few key factors about your base material and application to help you make the right choice. There are many different filler metal alloys available that are designed to provide varying characteristics. Choosing the right fit will help ensure that you produce a sound, long-lasting weld.