Magnalium refers to an alloy of aluminium with 5-50% magnesium. Trace amounts of other elements are added to improve hardness. It finds use in engineering and pyrotechnics.
Alloys with smaller amounts of magnesium (about 5%) exhibit greater strength, greater corrosion
resistance, and lower density
than pure aluminium. Such alloys are also more workable and easier to weld than pure aluminium. Alloys with high amounts of magnesium (around 50%) are brittle and more susceptible to corrosion than aluminium.
Although they are generally more expensive than aluminium, the high strength, low density, and greater workability of alloys with low amounts of magnesium leads to their use in aircraft
parts. Alloys with about 50% magnesium are brittle and corrode
easily, which makes them unsuitable for most engineering uses. However, these alloys are flammable when powdered, are more resistant to corrosion than pure magnesium, and are more reactive than pure aluminium and are therefore used in pyrotechnics
as a metal fuel
and to produce sparks.
Notes and references
http://www.vk2zay.net/article.php/85 (Making Magnalium)