Aluminium is a better conductor of electricity than Magnesium yet are in the same period of the periodic table explain

Resistivity: Mg 43.6 nanoohm.metre; Al 28.2 nanoohm.metre

Hardness: Mg 1.5 Moh; Al 2.75 Moh

So for equivalent volumes, aluminium is almost twice as conductive and half as soft as magnesium.

And magnesium is much more reactive than aluminium. It even reacts with water at temperatures slightly higher than room temperature. It is highly flammable especially in the form of powder and shavings - hence it is a popular additive to incendiary bombs.

So all in all, magnesium as a conductor is more trouble than it is worth.