Magnesium Solution
Overview
Magnesium alloys are alloys based on magnesium with other elements added — typically aluminium, zinc, manganese, cerium, thorium and a small amount of zirconium or cadmium. The most widely used are magnesium–aluminium alloys, followed by magnesium–manganese and magnesium–zinc–zirconium alloys.
Magnesium alloy is the lightest metal structural material in practical applications, with a density of around 1.8 g/cm³ — about two-thirds that of aluminium and one-quarter that of steel. Its specific strength is high, making it a strong candidate to replace aluminium and steel across automotive, electronics, aerospace, and military fields.
At the same time, magnesium alloys can be widely used in automobile, electronics, textile, construction and military fields due to their excellent casting, extrusion, cutting and bending properties.
Light weight — magnesium metal is currently the lightest metallic structural material in practical use anywhere in the world.
High specific strength — the ratio of strength to mass of magnesium alloy is high, and it has a certain bearing capacity.
Good rigidity & damping — the elastic modulus is small, the rigidity is good, the earthquake resistance is strong, and long-term use is not easy to deform.
No pollution to the environment — fully recyclable with no harmful byproducts during production or recycling.
Anti-electromagnetic interference and good shielding — magnesium alloys provide effective EMI shielding for electronic enclosures and housings.
Material Properties
Although the specific gravity of magnesium alloy is heavier than that of plastics, the strength and elastic modulus per unit weight are higher than those of plastics. In the case of parts, magnesium alloy parts can be made lighter and thinner than plastic parts. The specific strength of magnesium alloy is also higher than that of aluminum alloy and iron; the weight of aluminum or iron parts can be reduced without reducing the strength.
Although the thermal conductivity of magnesium alloy is not as good as that of aluminium alloy, it is dozens of times higher than that of plastics. Therefore, magnesium alloys are used in electronic products to effectively dissipate heat from the heat-generating electronic components to the case. It is also used in the dissipation points of computers and projectors that generate high temperature inside the body.
The electromagnetic wave shielding performance of magnesium alloys is better than that of electroplating-shielding alloys or plastics. Therefore, the use of magnesium alloys can reduce the shielding layer, thus reducing the cost of the shielding films. Application range: Magnesium alloys are used in the casing and shielding materials of mobile products.
Magnesium alloys have less cutting resistance than other metals, and can be machined at a faster speed during machining.
Magnesium alloy has higher deformation resistance than other metals, and can be caused by impact is smaller than other metals. Due to the good absorption performance of magnesium alloy to vibration energy, it can reduce vibration when used in strong and transmission parts.
Magnesium creep less dimensionally with time and temperature. Unlike plastics, recycled magnesium alloys can be machined without critical mechanical properties. Magnesium alloys have a low melting point and a small specific heat — the energy consumed during regeneration is only 5% of that for raw material.
Manufacturing
Magnesium alloy forming is divided into two methods: deformation and casting. Currently, the casting forming process is mainly used. Magnesium alloys can be formed by sand casting, lost foam casting, die-casting, and semi-solid casting.
Thixoforming is an environmentally friendly, high-speed, net-shape semi-solid magnesium injection molding process. In one step, the process transforms room-temperature magnesium chips into formed parts with a high degree of complexity and dimensional accuracy. Thixoforming is very similar to plastic injection molding in terms of mechanics, tooling and process fundamentals. Designers with experience designing plastic injection parts will find themselves familiar with designing Thixomolded products.
Finishing
The surface treatment technology of chemical conversion coatings is usually used for the protection of magnesium alloys. The final step in corrosion protection is the application of an organic coating on the surface.
The main function of organic coating is to play a role in further corrosion protection and decoration. Due to the characteristics of the organic coating after the magnesium alloy is treated with chemical conversion coating, the coating can be directly formed on the magnesium alloy surface treated with anodized polarisation or chemical conversion coating.
We can do magnesium alloy surface treatments according to customer needs: passivation, powder coating, and painting and even mock gold painting.
The commonly-used welding methods for magnesium alloys include:
TIG (Tungsten Inert Gas) Arc Welding
MIG (Metal Inert Gas) Arc Welding
Resistance Spot Welding (RSW)
Friction Welding (FW)
Friction Stir Welding (FSW)
Laser Welding (LBW)
Electron Beam Welding (EBW)
Welding Methods
Heats and melts the joint area of the connected components to fuse them. In most cases, filler metal needs to be added to form a joint after condensation. Methods include arc welding, gas welding, electron-beam welding, laser welding and electroslag welding — though most fusion methods are well suited to magnesium.
Magnesium and oxygen have a high affinity, so traditional gas flow arc welding is not suitable. TIG welding uses AC current for cathodic cleaning to remove oxide film and can weld magnesium alloys with or without filler metal, especially suitable for thin plate welding. For plates thicker than 6–12mm, AC welding machines with larger penetration depth are developed.
The heat source of gas welding is concentrated, leading to large shrinkage stress. Gas welding is mainly used for welding repairs or less important thin-plate components. For workpieces with thickness greater than 3mm, preheating to 300–400°C before welding. For plates thicker than 12mm, multi-layer welding is recommended.
Electron-beam welding has advantages of high energy density, fast welding speed, narrow weld and small deformation. Laser welding offers high energy density, less heat input, small residual stress, and does not require vacuum conditions. Laser TIG hybrid welding can increase welding speed by approximately 3× compared to TIG welding alone.
Combines friction, pressure, and thermal diffusion to overcome surface roughness and remove oxide film. It includes resistance spot welding, friction welding, and brazing.
Welding Difficulties
Due to the extremely strong oxidizing properties of other elements, the low melting point MgO (2852°C) and high melting point (2072°C) and low density, which is easy to form impurities in the weld. Magnesium also easily reacts with nitrogen to form impurities.
Due to the high thermal conductivity, high-power heat source and short welding speed, high-power heat source is likely to cause coarse crystals when welding. The grain growth is likely to cause coarse crystallizing and grain growth in the weld, which is likely to result in crystal cracking.
Magnesium alloy has a large thermal expansion coefficient (about 1 to 2 times that of aluminum), which is prone to large welding stresses during the welding process, resulting in large residual stress.
Since the surface tension of magnesium is smaller than that of aluminum, easy collapse is easy to affect the quality of base formation.
Magnesium alloys are prone to hydrogen gas holes during welding. Since the solubility of hydrogen in magnesium decreases sharply with temperature, the density of magnesium is lower than that of hydrogen, which means it is not easy to escape, resulting in air holes during solidification.
Magnesium alloys are prone to form a low-melting eutectic structure with other elements (e.g. aluminum, zinc, copper) that can form in isolated joints. When infrastructure is at the point is too high, the cooling deformation is the joint structure will crack at the grain boundary ("hot cracking").
