Titanium is considered to be an exotic metal due to its low weight, good strength, and corrosion resistance. However, in the past, it was believed that proper titanium welding can be performed only in sealed chambers.
It’s a reactive metal that can become contaminated by atmospheric gases. But welding titanium is actually not as difficult as many welders think. You just need to maintain proper gas shielding during welding, the rest is very similar to welding other types of metals.
Titanium and its alloys are most often welded with the gas tungsten arc (GTA or TIG) and gas metal-arc (GMA or MIG) welding processes. Resistance, plasma arc, electron beam, and friction welding are also used on titanium to a limited extent. All of these processes offer advantages for specific situations.
Titanium and most titanium alloys are readily weldable, using several welding processes. Properly made welds in the as-welded condition are ductile and, in most environments, are as corrosion resistant as the base metal. Improper welds, on the other hand, might be embrittled and less corrosion-resistant compared to the base metal.
The techniques and equipment used in welding titanium are similar to those required for other high-performance materials, such as stainless steel or nickel-base alloys. Titanium, however, demands greater attention to cleanliness and to the use of auxiliary inert gas shielding than these materials.
Molten titanium weld metal must be totally protected from contamination by air. Also, hot heat-affected zones and the root side of titanium welds must be shielded until temperatures drop below 800°F (427°C).
Titanium reacts readily with air, moisture, grease, dirt, refractories, and most other metals to form brittle compounds. The reaction of titanium with gases and fluxes makes common welding processes such as gas welding, shielded metal arc, flux-cored arc, and submerged arc welding unsuitable.
Likewise, welding titanium to most dissimilar metals is not feasible, because titanium forms brittle compounds with most other metals; however, titanium can be welded to zirconium, tantalum, and niobium.
In spite of the precautions, which need to be taken, many fabricators are routinely and economically welding titanium, making sound, ductile welds at comparable rates to many other high-performance materials.
One of the important benefits of welding the commercially pure grades of titanium is that they are over 99% pure titanium and there is no concern for segregation. The same is true of weld wire or rod in commercially pure grades.
Most titanium welding today is done in the open fabrication shop, although chamber welding is still practiced on a limited basis. Field welding is common. Wherever the welding is done, a clean environment is necessary for which to weld titanium.
A separate area, specifically set aside for the welding of titanium, aids in making quality welds. This area should be kept clean and should be isolated from dirt-producing operations such as grinding, torch cutting, and painting. In addition, the welding area should be free of air drafts and humidity should be controlled.
One of the most important factors in determining a quality titanium weld is the proper preparation of the weld.
- Clean the surface of the titanium to eliminate any impurities and remove any oil, grease or dirt. It’s best to use chemicals specifically designed for titanium. Remember that the cleaner the titanium will be, the stronger your created weld will be.
- To remove the contaminants, you can use a steam cleaner or a diluted solution of sodium hydroxide.
- Use a small hot-air blower to ensure that there’s no moisture left on the surface. However, make sure that you don’t use it on any flammable solvents.
- Make sure that all the welding parts are also clean and dry.
- Never use any chlorine-based cleaning solution on titanium.
- Even your hands can be a source of contamination. But keep in mind that rubber gloves can contain chlorine, so instead, opt for plastic or cotton gloves.
- Before striking the arc, make sure that the solvents that you were using to clean the surface have fully evaporated, as they usually have a low flash point.
Choose a Shielding Gas
Since titanium reacts readily with air, oil, dirt, moisture, and other metals to form brittle compounds, using the right shield gas is essential when you’re looking to ensure that you end up with a strong weld. Usually, most welders use 99.999% pure Argon for the process. Only really pure Argon and Helium provide optimal protection from the atmosphere.
When you buy the shield gas for your welding project, make sure that you only get this gas from trusted suppliers. Even if the Argon is slightly less pure than required, it can result in discoloration. You will end up with a yellowish-tinged weld, which is not something that you want to happen. Impure gas or incomplete coverage can also cause blue tinting and mottling.
With titanium, you need to ascertain that not only the front but also the back is kept protected from the atmosphere. Any area that is heat affected will have an adverse reaction if it comes in contact with oxygen.
For smaller parts, you can use enclosed compartments made out of glove boxes that are filled with shielding gas. You can even use specially made polyethylene purge gas chambers combined with a purge monitor. With them, you can verify that the chamber has enough Argon to provide optimal protection.
If you’re looking to have an ideal level of coverage while you’re welding, here are three steps that you need to follow:
- Primary Shielding – it is usually built in the welding torch and provides primary coverage necessary for protecting the molten weld puddle. You can use a standard, water-cooled torch that’s equipped with a ceramic cup and gas lenses. We suggest that you choose a torch with a broader cup for the best coverage.
- Secondary Shielding – Trailing shields provide secondary protection. They are attached to the end of most welding torches and guarantee that all heat-affected areas are kept safe from contamination.
- Backup Shielding – These devices look similar to trailing shields and serve virtually the same function. They are either handheld devices or are taped into position. They rarely ever come pre-fit into the welding torch.
Selecting the Right Filler Wire
When choosing the filler metal to weld titanium and its alloys, we suggest you choose a filler wire that primarily holds the same properties as the base material. You can also select a wire that is categorized in a strength level that’s one grade below the base metal. In some situations, the welder may even use a different category of filler wire altogether.
Your choice of filler wire will depend on the properties and the combination of the joint. To improve joint ductility:
- When welding unalloyed titanium of higher strength, use a filler metal that is lower in yield strength of the base.
- You can use unalloyed filler material when welding titanium from the Ti-5A1-2.5Sn and Ti-6A1-4V classifications.
- Another option is filler metal with lower percentages of oxygen, nitrogen, hydrogen, carbon, and other alloying contents than the base metal.
Usable Welding Processes
When welding titanium and titanium alloys, you can use any of the following welding procedures:
- Electron-beam welding (EBW)
- Gas-tungsten arc welding (GTAW) or (TIG) tungsten Inert Gas Welding
- Resistance welding (RW)
- Laser-beam welding (LBW)
- Plasma arc welding (PAW)
- Gas-metal arc welding (GMAW) or (MIG) Metal Inert Gas
- Friction welding (FRW)
1. Electron Beam Welding
This is a fusion process that utilizes a high-velocity electron beam to join two metals together. When the beam comes in contact with the metal pieces, it generates intense heat. The two plates melt and fuse to form a solid joint. Aerospace and aircraft production industries utilize electron beam welding because of the durability of the joints produced.
You can use the electron beam welding procedure for plates ranging from 6mm to 76mm and more. The process produces high-quality welds with low contamination levels as the process takes place in a high vacuum atmosphere.
2. Tungsten Inert Gas/GTAW
TIG or GTA welding processes use a non-consumable tungsten electrode that transfers current to the welding arc. Shielding gas is used to protect the weld puddle from external contamination, which can result in weak and low-quality welds. In the process, you need a filler metal or wire for the weld joint.
It is a widely used process for welding titanium and its alloys. You can use TIG without a filler material for square butt groove joints on base metals up to 2.5 mm in thickness. For thicker sheets, you need to use a filler metal to guarantee that the resultant weld joint is durable.
3. Resistance Welding (RW)
Resistance Welding is a thermo-electric procedure. It joins two pieces of metal together by passing a controlled current through the plates for a controlled period. It is common to use a significant amount of pressure for the procedure as well. In this method, heat is strictly restricted to the area that needs to be joined.
You can use resistance welding to join titanium and its alloys for spot or continuous welds. It is particularly useful when it comes to welding titanium with other metals like carbon steel or stainless-steel plates.
4. Laser-Beam Welding (LBW)
This is another fusion welding process that joins two pieces of metal together via a laser. It heats the intersection between the two plates, which melt and merge, forming the joint. Once the molten weld puddle cools down and solidifies, it results in a firm, durable weld.
Welders now increasingly prefer laser beam welding for titanium as it removes the need for a vacuum chamber. However, the use of shielding gas is still a must because the risk of contamination remains.
Even though a laser beam and electron beam are both fusion welding procedures, the scope of the former is more restricted. You cannot efficiently use the process on titanium plates more than 13mm in thickness.
5. Plasma Arc Welding (PAW)
Plasma Arc Welding is similar to TIG as it also uses an arc between a tungsten electrode and the workpiece. It is suitable for use on almost all titanium classifications and performs well even on thicker sheets of metal. Using the keyhole technique, you can also use it on a one-pass plate up to 13 mm thick.
6. Metal Inert Gas (MIG)/ Gas-Metal Arc Welding (GMAW)
MIG welding uses a solid filler metal wire that is continuously heated and fed via a welding gun. The process warrants the use of shielding gas to protect the weld puddle from contamination. Many welders prefer GMAW for its high metal deposition and productivity rates.
You can also use the process for titanium welds on plates that are more than three 3mm thick. Using the pulsed current technique, you can produce high-quality welds. The method proves less costly than others, especially for use on titanium plates more than 13mm thick.
7. Friction Welding (FRW)
As the name implies, the method uses friction to join two pieces of metal together. It is a solid-state weld process in which the resultant joint is as strong as the base. It’s widely used in various industries and is useful for joining pipes, tubes, or rods. It performs particularly well in situations where you can achieve joint cleanliness without the use of additional protective measures.