A Comprehensive Guide: Mastering the Art of Welding Magnesium

Welding magnesium alloys requires a delicate touch and a deep understanding of the material. Despite its challenges, mastering the process opens up opportunities in various industries, from aerospace to machinery. In this guide, we’ll explore the intricacies of welding magnesium. These include safety measures, alloy considerations, preparation techniques, and the preferred welding process.

Challenges of Welding Magnesium:

While welding magnesium shares similarities with aluminium,there is a critical distinction. When it comes to magnesium, there lies the potential for catastrophic joint failure if mistaken for aluminium. You can use plain white vinegar to differentiate between aluminium and magnesium alloys. Just pouring a few drops on a clean metal surface will tell you which material it is from. Magnesium will cause vinegar to start foaming up, while aluminium will have no reaction. 

Magnesium reacts with oxygen and creates a magnesium oxide on its surface, just like aluminium. This oxide must be removed before welding because it has a higher melting temperature. So if you don’t remove the oxide layer, it can get trapped in the weld as inclusions and weaken the joint.

Magnesium castings are often soaked in oil during their life cycle. Usually, shafts, bearings, gears, and other machinery parts are made from magnesium alloys. Once they break, it’s often cheaper to repair them instead of buying a new part. However, the oil gets soaked into the magnesium casting and gets logged deep into the casting pores. Since these machinery parts are exposed to high-temperature differences, the pores expand and contract and can trap oil deep beneath the surface. This can make welding magnesium parts quite challenging, depending on the oil intrusion severity.

Magnesium has a very high thermal conductivity and expansion rate. Therefore you must use concentrated heat and account for the material’s expansion. The joint or repair area shouldn’t be constrained to prevent cracking. In addition, the welding arc is obstructed by the zinc reaction in the puddle. It takes a lot of skill to weld magnesium because it requires a tight arc and won’t give you a clear view of the arc at the same time. We recommend first becoming proficient with welding aluminium before you try welding magnesium.

Safety Measures:

Welding magnesium alloys presents unique safety challenges, primarily due to the metal’s high flammability and the potential presence of hazardous elements like zinc. Apart from zinc content, magnesium itself poses a huge safety risk. Magnesium is a HIGHLY flammable metal. It’s so dangerous that once it catches fire, you CANNOT extinguish it with water or carbon dioxide! It can literally break molecular bonds of H2O, release individual atoms of hydrogen and oxygen, and use them as fuel! So, if it catches fire, pouring water would be as if you added gasoline to the fire! 

Weldability of Magnesium Alloys:

Magnesium is often combined with other materials to increase its strength and suitability for various applications. The designation for these magnesium alloys often consists of one or two letters indicating the specific alloying elements, followed by the percentage of each element in the alloy. For example, the ASTM designation AZ91C indicates an alloy containing 9% aluminium and 1% zinc.While some alloys enhance weldability such as added aluminium, high zinc content can lead to cracking issues. 

While magnesium-thorium alloys stand out for their excellent welding properties, because they are resistant to cracking. Plus weldments made with these alloys do not require stress relieving. On the other hand, certain magnesium alloys are prone to stress corrosion, and weldments used in corrosive environments may crack over time if residual stresses are not relieved through stress relieving.

Preparing Magnesium for Welding:

It’s crucial to that you clean and prepare the joint before welding. You can start by using acetone to wipe the part clean. Then, use a carbide burr with a die grinder to remove the magnesium oxide around the joint area and to prepare a nice groove inside the casting crack, if you are repairing a cracked casting. You can also use an angle grinder with a wheel that won’t load up when grinding magnesium, but carbide burrs work the best. Just make sure your carbide is coarse. 

Since most magnesium welding jobs are actually casting repairs, you’ll often have to grind away cracked metal and rebuild the lost material with welding. This involves melting filler rods into a casting shape to fill the lost material you grinded away. Afterward, the part will be machined again and be like new. 

TIG Welding Magnesium:

We highly recommend using a TIG welding process to weld magnesium. Of course, you can also use a MIG welding process and other welding methods like resistance, spot, flash, seam, and oxy-fuel welding. However, the TIG welding method works best for most manual welding jobs because it provides the best arc visibility, heat input control, and welding with alternating current.

Since magnesium has an oxide layer on its surface, like aluminium, it’s highly beneficial to use AC TIG welding. The alternating current oscillates between DCEP and DCEN to simultaneously achieve oxide removal and penetration. Of course, you need to use a high frequency arc start to reduce any possible contamination, since magnesium is a sensitive metal. 

TIG welders like the TIG325X AC/DC TIG Welder With Foot Pedal should be your choice. It supports high frequency arc ignition and AC TIG welding. In addition, it can weld using a pulsed TIG welding process to help you narrow the arc cone just right and focus the temperature input into the cracked groove you are trying to repair. Since magnesium conducts heat rapidly, just like aluminium, you’ll need to focus your arc on the joint to provide the necessary fusion. 

You may benefit from preheating the thick parts to about 150°C.  But, if you are welding thick parts, consider getting a TIG welder with high amperage output. Our YesWelder TIG250P AC/DC can output 250A at 60% duty cycle, letting you weld moderate thickness for a prolonged period of time. But be careful not to input too much heat, either. Excess heat can lead to cracks and embrittlement in the heat affected zone. You should only use enough amps to get the puddle going when welding magnesium, not more.

Shielding Gas Selection:

Choosing the right shielding gas is critical. While 100% helium may amplify arc potential by helping you squeeze every bit of energy coming out of your welder, it is not recommended. A 50/50 argon/helium mix is often preferred for stability and arc control. Helium’s excessive heat input can compromise arc stability, making argon a necessary component. On the other hand, TIG welding magnesium requires a tight arc, so if you use 100% helium, you may lose some arc stability provided by argon.

Filler Metal Selection:

The four most commonly used filler metals to weld magnesium alloys are ER AZ61A, ER AZ101A, ER AZ92A, and ER EZ33A. You can buy these as MIG spooled wires if MIG welding, or as TIG welding rods for the TIG welding process.

The table below summarises the filler metal selection when welding magnesium castings, which is what most magnesium welding jobs require. 

The AZ101A welding rod is the most popular choice and works quite well for welding magnesium castings where no welding procedure is provided. So, if you are hired to repair a casting, but there is no welding specification sheet, or the client doesn’t know which magnesium alloy casting is made from, using the AZ101A filler rod is safest. The AZ101 contains 10% aluminium. As a result, it enriches the weld pool with aluminium without introducing a high amount of zinc, which helps prevent cracking.

Don’t forget to clean off the oxides from the filler wire. Magnesium really loves oxygen. So, if your filler metal wires package was opened some time ago, you’ll have to clean the oxides from the wire.

Tungsten Electrode Selection:

For TIG welding, pure tungsten, zirconiated tungsten, or thoriated tungsten electrodes are suitable. Green and white tungsten are recommended for alternating current usage. For a more in-depth guide on choosing the right tungsten check out our previous blog post.

Travel Angle And Welding Speed

You should bring the filler metal wire as horizontally as you can when welding magnesium in the flat position. Add the filler wire to the edge of the weld puddle, much like when welding aluminium. 

The TIG torch should have a slightly leading angle in the direction of your travel. Try to weld quickly to avoid excessive heat input and maintain a steady, consistent travel speed. 

Final Thoughts:

Welding magnesium alloys demands practice and precision. It’s advisable to start with scrap pieces before attempting complex projects. While MIG welding is an option, TIG welding, especially with AC TIG, remains the preferred method for its oxide-cleaning capabilities and enhanced arc visibility. Mastering magnesium welding opens doors to lucrative opportunities, given the high cost of replacing magnesium castings.

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