Magnesium

Magnesium is the lightest metal with a density of 1.74g/cm3 which represents two thirds of that of aluminum (2.69g/cm3). As for aluminum, magnesium has also a high thermal conductivity combined with a high coefficient of thermal expansion. Its melting point of 650°C is comparable to that of aluminum. Its reaction with oxygen gives a protective oxide surface MgO which ensures its atmospheric corrosion resistance.

The weldability of magnesium is improved when alloyed with 10% of aluminum because of the refining effect of the latter on the microstructure. Magnesium alloys containing more than 1% Zn are prone to hot fissuring. Also, Mg-Zn alloys are considered unweldable by arc welding. Similarly to aluminum, the more common welding processes used for welding magnesium are:

• MIG for thick sections,
• TIG for quality welding on thin sections with:
• high frequency alternating current AC for thicknesses above 5mm;
• DC+ (DCEP) for thicknesses under 5 mm
• Flame welding under carburizing flame