Frank Wilson
Senior Editor
You can weld a wide variety of materials, all with their own unique mechanical properties and applications, including titanium, a lightweight and robust metal.
Each metal and alloy has its own unique characteristics, and titanium is no exception. While the preparations necessary for welding titanium are similar to those for other materials, titanium has its own quirks.
What’s so special about titanium alloys, and why should you look more closely at your technique when using them than other metals?
What is Titanium?
Titanium and its alloys are known for their high strength-to-weight ratio, corrosion resistance — including acids and chlorides — light weight, toughness, and high melting point. One of the most common industrial grades of titanium, grade 5 (Ti-6Al-4V), has an ultimate tensile strength of 130,000 psi and yield strength of 120,000 psi.
Although titanium alloys are often more expensive initially than other metals, such as stainless steel and aluminum, titanium represents a long-term investment due to its durability. Titanium alloys are used in everything from aerospace and military applications to surgical implants and commercial goods.
There are a wide variety of titanium grades, each fulfilling a different requirement regarding weldability, formability, and tensile strength, for different applications and manufacturing processes. When learning how to weld titanium, it’s worth exploring the different grades and developing a thorough understanding of this metal’s characteristics.
Preparation
Titanium alloys are reactive metals. At or near room temperature, titanium alloys react with the oxygen in the air to form an oxide layer called titanium dioxide.
This hard, protective coating is highly corrosion resistant. However, this oxide layer also has a higher melting point than the base metal, so you’ll need to remove this coating before welding. If the oxide enters the weld pool, it could interfere with the weld joint’s mechanical properties. You can remove this layer with a die grinder and a carbine deburring tool.
To prepare your equipment, always clip off the filler rod’s end after every welding session to avoid introducing impurities into the welding pool.
Cleaning
Titanium alloys are reactive metals. At or near room temperature, titanium alloys react with the oxygen in the air to form an oxide layer called titanium dioxide. This hard, protective coating is highly corrosion resistant.
However, this oxide layer also has a higher melting point than the base metal, so you’ll need to remove this coating before welding. If the oxide enters the weld pool, it could interfere with the weld joint’s mechanical properties. You can remove this layer with a die grinder and a carbine deburring tool.
To prepare your equipment, always clip off the filler rod’s end after every welding session to avoid introducing impurities into the welding pool.
Lubricating oils, coolants, and other contaminants can cause weld embrittlement or other defects, leading to weld failures or a reduction in the weld joint’s strength. As a general rule, you should always ensure that your workspace and equipment are clean and tidy before preparing to weld.
Clean the base metal and package any parts that you do not immediately need for welding. This allows you to avoid contaminating them inadvertently during other work-related tasks.
When cleaning the base metal’s surface, consider using chemical cleaning agents specifically designed for titanium. You’ll need to remove any oil, grease, or debris. You may want to use acetone or other thinning agents to clean the surface thoroughly.
You may also use a carbide file, but it’s recommended that you only use it for titanium and nothing else. A steam cleaner or sodium hydroxide solution can also work, but make sure to use a hot-air blower to remove any remaining moisture from the work surface.
Avoid heating solvents that may be flammable. Chlorine can affect the weld too, so it’s advisable to wear plastic or cotton gloves rather than those made from rubber.
Reactive Metals Require Gas Shielding
Any discussion regarding how to weld titanium must begin with proper shielding. As titanium is a highly reactive metal, gas shielding is essential. When heated, titanium becomes even more susceptible to absorption of atmospheric contaminants and gases, including oxygen, nitrogen, hydrogen, and carbon, affecting the weld.
When titanium absorbs these chemicals, it forms oxides. You need to pay special attention to gas shielding to ensure that your titanium weld does not lose strength, ductility, or other mechanical properties needed for a high-quality, long-lasting part or product.
Argon is one of the most commonly used shielding gases in welding. When selecting a shielding gas, you need to determine its purity. If the argon is impure — less than 99.999% — it may affect the weld. The reactive nature of titanium requires that you shield the entire weld zone.
You’ll need to keep the metal purged with argon until it cools. There is some disagreement among welding authorities on the precise temperature that the titanium can cool to before you can safely remove the shielding gas. Some argue less than 800°F, others less than 500°F.
Titanium Discoloration
Titanium discoloration can indicate either the oxide layer’s thickness or the degree of contamination. As a result, it can indicate the quality of the weld and the material’s mechanical properties.
If the weld is silver, straw-colored, bronze, or brown, it’s acceptable. Blues, dark and light, violets, and greens indicate that the weld has potentially been compromised, and the part may be rejected. However, if the welds are finished, blue and green discoloration may be acceptable. If further work is needed, you’ll have to remove this layer of material first.
Coloration is simply one method of determining weld quality. There are numerous methods of inspecting the material, from X-ray and hardness testing to ultrasonic and destructive testing. One or several of these may be necessary to confirm the material’s properties and viability.
Test Your Shielding
To ensure that your gas shielding is sufficient, consider applying your arc to a test piece first before beginning to weld the required workpiece. This can allow you to take stock of what variables you’ve accounted for and see whether you’ve missed anything during your preparations.
Purge Blocks
Purge blocks can act as heat sinks and gas lenses, evenly distributing the shielding gas to protect the part against atmospheric contamination. A purge block made from copper sheet and stainless steel is the best choice.
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Final Thoughts
In your career as a welder, you’re likely to weld a variety of different materials, but titanium is one of the most exotic that welders typically encounter. Most of the prep work for welding titanium overlaps with that required for other materials, especially cleaning, but titanium is highly reactive.
As a result, you need to ensure your cleaning and gas shielding are on point at all times, so you’ll be on your way to producing high-quality parts or products from titanium.
