Magnesium

Magnesium's great advantage is its low density compared with other metals such as aluminium and steel (alloy).  Magnesium components are 40% lighter than steel of the same strength.   Magnesium alloys can be cast and machined to give complex shapes.  In cars, magnesium alloys are used in steering columns, brackets and in alloy wheels.  By reducing the weight of the car fuel use is reduced and overall economy improved.   Many mobile phones have magnesium cases, as do lots of laptop computers.  The low density of the metal is a great advantage here.

Since magnesium is higher in the metal reactivity series than iron ( or the alloy steel) it corrodes more easily. Magnesium bars can be joined by wires to steel structures or pipelines. This sets up an electrical cell, with the more reactive magnesium as the anode ( + electrode). It is the magnesium which corrodes not the steel, it is a sacrificial anode. The magnesium is usually packed in a porous cotton bag filled with gypsum (calcium sulphate) and clay. This keeps the surroundings of the anode constant giving more effective protection to the steel