There are obviously materials property differences, such as capacity, weight, and cost between aluminium (Al) and copper (Cu) to consider for an electrical application. Al was more prevalent in the past for products such as bus bars, fuses, and breakers. Over time, some designers have changed components from Al to Cu. Today, due to cost stability and coating some designers are switching back.
Why is aluminium used instead of copper for overhead cables?
Because it’s cheaper and lighter than a copper wire of the same resistance per length; about 6 times cheaper and twice as light as copper. Aluminium has 61% conductivity of copper, but only 30% of the weight. So, a bare aluminium wire of half as much weight as a bare copper wire will have the same resistance, which is important in power transmission lines that span about a few hundred meters between towers.
Even if the prices of aluminium and copper were the same, this would also mean that an aluminium cable would cost half as much. Since aluminium is roughly about 3 times cheaper than copper, a bare aluminium cable would cost about 6 times less.