Properties of Magnesium: Understanding Welding Materials

Magnesium (Mg) is a silvery-white metal that ignites quickly in the air and burns with a bright light. It’s the eighth most abundant element in the Earth’s crust, but it is the third most plentiful structural metal, behind iron and aluminum. Trillions of tons of magnesium are in the ocean, which is the source of much of the 850,000 tons produced yearly.

Magnesium does not occur uncombined in nature. Instead, it is found in large deposits of magnesite and dolomite. It is typically prepared by reducing magnesium oxide with silicon or electrolysis of molten magnesium chloride. One-third less dense than aluminum, magnesium improves aluminum's mechanical, fabrication, and welding characteristics when used as an alloying agent. These alloys are useful in the aerospace and automobile industries.

 

Physical Properties of Magnesium

Physical Properties of Magnesium
Color	Silvery-white metal
Phase	Solid
Crystalline structure	Hexagonal
Ductility	Magnesium can be hammered into extremely thin sheets
Malleability	Magnesium can be shaped or bent
Luster	Exhibits a shine or glow
Hardness	Relatively soft
Melting point	The magnesium melting point is 651°C (1,200°F)
Boiling point	The boiling point is 1,100°C (2,000°F)

 

The physical properties are the observable characteristics without changing them into another substance. Those properties may include color, luster, freezing point, boiling point, melting point, density, hardness, and odor.

Chemical Properties of Magnesium

Chemical Properties of Magnesium
Chemical Formula	Mg
Compounds	Oxide, hydroxide, chloride, carbonate, and sulfate. Also, Epsom salts (magnesium sulfate heptahydrate) and Milk of Magnesia (magnesium hydroxide)
Flammability	Burns in the air with a bright white light
Reactivity	Upon heating, magnesium reacts with halogens to yield halides
Alloys	Magnesium alloys are light but strong
Oxidation	It combines with oxygen at room temperature to form a thin skin of magnesium oxide

 

The chemical properties are observable only during a chemical reaction. Reactions are brought about by changes caused by burning, rusting, heating, exploding, tarnishing, etc.

Mechanical Properties of Magnesium

Mechanical Properties of Magnesium
Brinell Hardness	30
Tensile Strength, Ultimate	13,000 psi
Tensile Strength, Yield	3,050 psi
Elongation at Break	2.0 to 6.0%
Modulus of Elasticity	6,380 ksi
Compressive Yield Strength	3,050 psi
Coefficient of Friction	.36

 

The mechanical properties help classify and identify the material. Common properties include strength, ductility, hardness, impact resistance, and fracture toughness.

Is Magnesium a Good Welding Material?

Magnesium has several properties that make it a helpful fabrication material. It’s lighter than aluminum and steel, yet it doesn’t sacrifice the strength required for structural integrity. It’s excellent for sound dampening and can be cast-formed or hot-formed. It’s also easily machined and recycled.

On the downside, magnesium alloys can have specific issues relevant to welding and fabrication. For instance, it has low elasticity, high shrinkage when it solidifies, and high reactivity to chemicals, including oxygen. But the most worrisome issue with magnesium alloys is corrosion resistance, and it’s why magnesium alloys take steps to enhance corrosion resistant properties of the subsequent material.

Tips for Welding Magnesium Alloys

How can you successfully weld magnesium alloys? Here are some suggestions for joining this unpredictable metal:

Clean the surface thoroughly: Magnesium can oxidize readily, so it’s usually coated with a thin layer of protective oil. The oil prevents oxidation, but it’s a contaminant that can put the weld at risk.

Be aware of the fire risk: Magnesium can ignite readily and be very dangerous in powder form. Before welding, remove dust or filings from any cleaning to avoid fire hazards.

Choose the correct welding method: TIG and MIG are excellent for most jobs.

Know when it’s best to weld magnesium: Magnesium welding is not often chosen for structural joining. Instead, it is a process for repairing castings with worn areas, fixing casting defects, or thermal and vibration cracks. These repairs are a cheaper alternative to recasting the piece.

Choose the suitable filler: Picking the appropriate filler rod for the magnesium alloy is critical. For example, AZ91, a common filler material, is a magnesium alloy with around 9% A (aluminum) and 1% Z (zinc). AZ101 is one of the most forgiving fillers, while other joint fillers include AZ61A, AZ92A, and EZ33A.

Preheat thicker pieces: Magnesium can crack under thermal stress, such as when welding around the heat-affected zone and preheating the material to around 200-300 degrees C. will help minimize the risk of cracking when welding magnesium alloys.

Use the suitable shielding gas: As a rule, argon, helium, or a mixture are the most common choices. Argon is the top pick for its low ionization potential and arc stability, and it also limits heat input and minimizes cracks and inclusions with a shallow arc penetration.

Try multiple passes: Heat management is essential when welding magnesium. Making one deep weld with filler material risks burning through the materials or threatening the strength of the area surrounding the joint.

Consider heat treating: Magnesium workpieces often require heat treatment to recover their strength after a repair. Without it, the repair could be another cause of failure next to it.

Use the right equipment: Always approach magnesium welding with the right equipment. Since TIG welding magnesium alloys is recommended, you should rent or buy a machine if you don’t own one. However, why would you want to rent a welder when you can own a high-quality TIG welder for less than $500? Shop online at PrimeWeld for affordable TIG welders offering flexibility for hobbyists and professionals.

What is Magnesium Used For?

Welding with magnesium alloys is popular in the aerospace, medical, and marine industries. Because they are strong, lightweight, and have excellent thermal conductivity, magnesium alloys are a top choice for welding parts and components for aircraft, boats, medical instruments, sporting equipment, and furniture.

Aircraft components must be lightweight and rigid to ensure safety, so it’s no surprise that aerospace manufacturers prefer magnesium alloys. Other aerospace applications include engine, exhaust, and landing gear components.

The medical industry uses magnesium alloys to create implants and medical instruments because of their strength and biocompatibility. These non-toxic alloys are ideal for medical devices that contact sensitive body areas.

The marine industry uses magnesium alloys for welding projects. Because they are strong and corrosion-resistant, they are perfect for boats, including their hulls, frames, propellers, and engine components.

Lightweight and durable magnesium alloys are also used in the sporting goods and furniture industries.

Recommended TIG Welders For Your Next Magnesium Project

PrimeWeld's best-selling, top-of-the-line TIG225X AC/DC TIG Welder meets the needs of both professional and part-time hobbyists. A foot paddle control, included in the package, ensures ease of use for operators of all experience levels. The TIG225X has a pulse frequency of 0.5 to 10 Hz for quality welds on those thin sections.

If you are looking for increased efficiency from a welder, look no further than the TIG200-D Inverter Welder. This compact, versatile unit produces high-quality welds at a transfer efficiency of above 85%.

Both TIG welding models are multi-use with both TIG and stick functions.

Remember, MIG welders are also recommended for welding magnesium alloys. With that in mind, the PrimeWeld MIG180 MIG Welder with Spool Gun is excellent for welding various metals. The MIG180 is easy to use and cost-effective, plugging into your 220V wall socket and running in minutes. These 180-amp arc welders use flux core wire to quickly weld thicker materials or a shielding gas for other welding processes.

Another versatile machine for both the experienced pro and the do-it-yourselfer is the MIG160 Flux Core MIG Welder. This machine also easily connects to a 110/120V wall outlet and will provide superior performance and quality at a competitive price.

The third MIG welder offered at PrimeWeld is the MTS200, a 3-in-1 TIG, MIG, and Stick welding machine. This unit is aluminum-capable, highly portable, and fan-cooled for longer welds.

Contact PrimeWeld for more information!