Many welders who do not have experience welding titanium or have not tried to weld it believe it is tough to weld titanium. However, welders who weld titanium day in and day out in their fabrication shop say that welding titanium is almost similar to welding stainless steel and nickel alloys. Of course, you need to take certain precautions and follow set procedures.
This article discusses the issues related to welding titanium like how to weld titanium, welding processes for welding titanium, filler wire for welding titanium, and also questions like can you MIG weld titanium, can you stick weld titanium, can you weld titanium with mild steel, and can you weld titanium with aluminium.
How to Weld Titanium?
Titanium is popular due to its lightweight and high strength-to-weight ratio. It is used in many industries today, including aerospace, marine, and military-related products. It is also used in atomic reactors.
Titanium is a super reactive metal (it becomes reactive at about 700º F), and if hot titanium is exposed to atmospheric air, it can react with different elements of air to form oxides, nitrides, and brittle carbides on its surface. Each of these compounds takes away the positive properties of titanium and affects the heat-affected zone (HAZ) when welded.
When exposed to atmospheric air, titanium forms an outer layer of titanium oxide at room temperature. This layer of titanium oxide must be removed before welding since the melting point of titanium oxide is much higher than titanium. When welding titanium, you should shield the molten weld pool as well as the hot weld metal behind it from atmospheric air and contaminants.
The melting point of titanium (1668º C (3034º F)) is higher than other metals and alloys (like the melting point of stainless steel is1510º C (2750º F), and the melting titanium can easily get oxidized (if allowed to come in contact with air) and contaminated during welding. Multiple layers of shielding are needed to protect against the contamination of titanium during welding.
The AWS (American Welding Society) structural welding code D1.9M/1.9M:2007-ADD1 released in 2007, talks about welding titanium. Interested persons can contact the American Welding Society to purchase this standard. This standard gives all the information required for welding titanium.
The design of weld joints for titanium is similar to stainless steel and other metals.
You can weld titanium by the following welding processes:
- GTAW/TIG welding.
- GMAW/MIG welding.
- Plasma arc welding (PAW).
- Laser welding or laser beam welding (LBM).
- Electron beam welding (EBM).
- Friction welding.
- Resistance welding.
Weld preparation for welding titanium
Preparing the titanium workpieces is highly important for achieving good quality titanium welding.
- Maintain your titanium welding area clean and free of dust and other particles that can contaminate the titanium welding.
- Remove the oxide coating on the titanium workpieces using a dedicated stainless steel brush. Clean the titanium workpiece surfaces to remove oil, grease, dirt, and other contaminants. You can use a mild solution of sodium hydroxide or a degreasing solution to do this. Wipe the welding surfaces clean and dry before you start welding.
- If you grind titanium (to remove the oxide coating), do not allow the titanium dust to accumulate. Titanium is a highly reactive metal, and the dust can be capable of catching fire.
- Use a dedicated stainless steel brush, carbide file, carbide deburring tool (like carbide rotary burrs), and other tools during titanium welding (to avoid contamination of welding).
- Modifying the welding torch to add a trailing shielding gas is essential. The trailing shield follows the welding torch.
- Use a nonporous and clean plastic hose for carrying the argon gas from the cylinder to the shielding. Please do not use a rubber hose since it can be porous and can absorb oxygen on its way.
- Wipe and clean the titanium filler wire and any tools used to handle titanium.
- When the titanium fabricated item is critical, you can use a hot air dryer to remove any moisture on the workpiece surface and ensure you are wearing dry gloves.
- Wearing gloves is essential when welding titanium because chlorine contained in your sweating hands can cause localized corrosion.
- When welding titanium, you must have argon all around the welding length to eliminate any absorption of oxides, contaminating and making the weld weak.
How to check titanium welding quality
The color of the weld can be an indicator of the quality of the titanium weld. Silver and bright weld bead usually is an indication of good quality titanium weld. A weld bead color of light straw (light yellow), dark straw (dark yellow), and brown may be acceptable for some applications, and this can be used after thoroughly cleaning the weld bead with a dedicated stainless steel brush. The color is due to the formation of the oxide.
If the color of the weld bead is violet, dark or light blue, green, gray, or white, the same may not be acceptable, and in that case, the whole weld bead is removed by grinding and re-welded.
Cleaning the weld bead between the multiple weld runs is not required if the weld bead is bright silver. However, if the weld bead is contaminated (dark blue or grey color), it has to be entirely removed by grinding and re-welded.
GTAW/TIG welding titanium
TIG welding is the welder’s first choice for welding titanium. TIG welding uses a non-consumable tungsten electrode, a handheld filler wire, and a shielding gas.
The major difference between TIG welding titanium and TIG welding metals like stainless steel is titanium welding needs pure argon shielding on the molten weld pool as well as on hot weld metal behind it (the weld bead behind the weld pool will be still hot enough to react with oxygen and other components of atmospheric air).
TIG welding gives better control (heat input, and the molten weld pool) to the welder compared to other welding processes and TIG welding has remote current control capability, post flow timer, and high frequency (non-touch) arc start.
As per AWS D10.5 thoriated (contains thorium oxide) and lanthanated (contains 1.3 to 1.7% lanthanum) tungsten electrodes are ideal for TIG welding titanium.
The shielding gas argon should be 99.999% pure and even the slightest impurity can cause the weld color to become yellow-straw. If you observe a blue tint in the welding that means something is wrong with the argon quality or its flow. The flow of argon should start well before you strike the high-frequency start arc.
TIG welding can use shielding gas at three places: primary, secondary, and backup shielding. You can use a dual flowmeter for the argon cylinder.
Primary shielding is through the welding torch to shield and protect the molten weld pool. Use a ceramic cup with a wider diameter (3/4ʺ) for the welding torch to allow more argon for shielding.
Secondary shielding: You can use a trailing shield of the argon gas by using a custom-made TIG torch.
Backup shielding: The backup shielding intends to provide argon protection of the root side of the welding and also the heat-affected zone (HAZ). This will be helpful for welding titanium pipes. A purge fixture can be made to provide argon shielding for butt welding workpieces.
Alternately, you can use an inflatable chamber or a sealed metal chamber filled with argon to provide an atmosphere free of air and contaminants for titanium welding. Such chambers will have the provision to insert your hands with gloves for doing the welding.
When you end the titanium welding, the weld pool is still hot and needs an argon shield’s protection until it cools down below 500º F.
You can use a transformer or inverter-based DC (direct current) power source and use DCEN (direct current electrode negative) setting for welding titanium. The TIG system should have a high frequency (non-touch) arc starting system because the tungsten electrode should not touch the titanium workpiece. Pulse TIG welding capability will help control the heat input and improve arc stability and penetration.
Before starting the actual welding, you can use a scrap titanium metal piece for trial welding to ensure everything is good.
TIG welding can be done with a single pass up to a thickness of 3 mm; after that, multi-pass welding may be required. This makes TIG not efficient for titanium welding of more than 3 mm thick workpieces.
The ingredients for a successful TIG welding of titanium are:
- Super high purity (99.999%) argon shielding gas.
- Clean workplace.
- Clean and dry titanium workpieces.
- Sufficient argon shielding all over the weld length.
- Use high-frequency non-touch arc starting.
- Use the recommended tungsten electrode and filler wire.
- Strictly follow the weld preparation procedure.
- Holding the torch in place with the argon on till the weld metal is cooled down to less than 500º F.
These tips ensure silver and shiny weld metal every time.
MIG weld titanium
You can MIG weld titanium; however, most welders prefer TIG over MIG for welding titanium. MIG welding is suitable for welding titanium of more than 3 mm thickness. There can be a risk of burning the metal if you MIG weld titanium less than 3 mm thick. MIG welding is economical for welding titanium metals of 1/2ʺ and above. MIG welding uses DCEP (direct current electrode positive) power.
A ceramic cup of 1ʺ diameter can be used for a MIG welding torch. Ensure sufficient shielding gas all over the weld length, similar to TIG welding.
There is a need for a higher productive titanium welding process, and MIG welding can meet this requirement. MIG welding uses a continuously fed consumable titanium wire electrode, and the arc is struck between the titanium wire and the titanium workpiece. An inert gas protects the molten weld pool and the hot weld metal behind it. The weld deposition rate is very high in MIG welding compared to TIG.
Helium is usually used as the shielding gas for MIG welding titanium; when you use argon as the shielding gas for MIG, the welding arc can become unstable during welding. MIG is considered to have the potential for efficient titanium welding; however, the issue of arc stability needs to be solved.
When MIG welding titanium, the layer of titanium oxide on the workpiece releases electrons easily (compared to base metal titanium) and leads to a phenomenon called wandering (as per the welding researchers), which tends to make the arc wander and results in defective welding, this issue (how to check this wandering) is being addressed to develop a workable MIG welding for titanium.
It was noticed that the issue of wandering could be controlled, and the quality of MIG welding titanium can be improved by applying a high-frequency micro-oscillation to the contact tip of the titanium wire.
Other welding processes for welding titanium
Plasma arc welding: Plasma arc welding is similar to TIG welding except for the difference in the welding torch. You can use plasma arc welding to weld titanium by following the standard weld preparation for titanium and following a process similar to TIG welding. In addition, you can use the keyhole method for higher penetration.
Laser welding: Laser beam welding is another process you can use for welding titanium. Using high purity argon (99.999%) and shielding the molten weld pool as well as the hot weld metal (behind the weld pool) is important. You must also ensure the argon shield continues till the weld metal cools down to less than 500º F. The standard weld preparation for titanium needs to be followed.
Electron beam welding: Electron beam welding is a special welding process and is done in a complete vacuum, and the contamination level is very low. This welding process is extensively used in aerospace, marine, and automobile industries. This process needs high capital investment.
Resistance welding: You can use resistance welding for joining titanium to other metals like stainless steel or ordinary steel. However, you cannot expect super high-quality welding. Inert gas shielding may or may not be required.
Friction welding: Many industries use the friction welding process to join titanium pipes, tubes, and rods using this method. Care may have to be taken to create an inert atmosphere surrounding the welding area.
Titanium welding wire
The filler wire for titanium welding is included in AWS standard A5.16-70. Selecting a filler wire with the properties and composition of the titanium workpiece (base metal) is recommended. A filler wire with strength one step below the workpiece metal is selected for some applications. The choice of the filler metal depends on the welding process.
Some popular filler wires used for TIG and MIG titanium welding are AWS A5.16 ERTI-2, AWS A5.16 ERTI-3, and AWS A5.16 ERTI-5.
Can you stick weld titanium?
No, you cannot use stick welding for titanium because titanium welding requires a good shielding gas to protect the molten weld pool and the hot weld metal from the atmospheric air and contaminants. The shielding gasses that come out of the stick welding electrode’s burning flux are incapable of providing the expected shielding.
Can you weld titanium to mild steel?
Explosive welding is solid-state welding and is used in a limited way for welding titanium to mild steel. TIG or MIG welding of titanium to mild steel can be tried by following all the procedures. However, the quality of the weld cannot be guaranteed.
Can you weld titanium to aluminum?
This is a difficult task due to the massive difference between the melting point of titanium and aluminum. However, it is observed that there are specific applications in the aerospace industry where parts of titanium and aluminum are welded.
Explosive welding is solid-state welding and is used in a limited way for welding titanium to aluminum.
Conclusion
Titanium as a metal has been gaining popularity over the years due to its multiple advantages. It has applications in critical industries like aerospace, marine, atomic reactors, and defense-related products. A welder who can fabricate titanium can command respect as well as money. We do hope this article has given some insight into the topic.
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