I mean doesn't aluminium have more free electrons than copper? Like in metallic bonding the metal loses its outer electron to become a neutral atom. So aluminium has 3 electrons on its outer shells so wouldnt that be better?
Aluminum is the electrical conductor of choice for high voltage, high-power applications. However, its use in low voltage, residential applications is very limited. Aluminum offers excellent conductivity, is light in weight (a major factor in both installation and also in sizing the structures that hold conductors), and is relatively inexpensive. But aluminum has two characteristics that are problematic. 1. Cold flow: this is the property that results from aluminum being a fairly soft material. When it is subjected to pressure, for example in an electrical connection, aluminum tends to gradually conform to the pressure that is applied in the joint, with the result that over time, the joint becomes loose. A loose joint presents more resistance, and current through resistance produces heat. In the 1950's, there were attempts to use aluminum wiring in residential applications, but there were many instances of fires that resulted from these loosened connections. It is possible to overcome the cold flow problem by using special connectors that apply constant pressure (basically, spring-loaded fittings), but these are not practical in low-voltage residential applications. 2. Oxidation: when aluminum oxidizes, it forms a non-conducting skin that is essentially invisible. This oxide can further increase the resistance in a connection and add to the fire hazard. The solution to this problem is to use special conducting grease in the connection - the grease seals the surface from air to prevent further oxidation, and fine zinc particles in the grease penetrate any oxide layer that might already be there to reduce resistance. Unfortunately, the use of conducting grease is also inappropriate for residential low-voltage applications. Today, aluminum conductors are commonly used for the main service entrance in a home.. But aluminum wire is no used for ordinary lighting and receptacle circuits.
It is used where low weight is important, such as transmission lines and in aircraft. Probably in autos in the near future. (Below is for North America only) In homes, it has a bad history. It was allowed at one point in the 60s, but it was found that connections between copper wire and aluminum wire tended to loosen up due to different rates of thermal expansion, and thus cause overheating and fires. It can still be used if you use the proper methods at the interface between the two materials. But there are now revised standards that solve that problem, and aluminum wire is allowed for use in residences (in some states, others have not yet changed their laws). And I believe it is in use in new commercial buildings. But not in residences, as there are still issues with insurance companies not insuring homes with the new wiring. There are problems differentiating between older (1960s) aluminum wire and new wire, and the types of connection (switches, outlets, breakers) used.
It was tried several years ago for transmission lines, but was scrapped because Aluminum has too low of a melting point, and it also goes to liquid state very quickly when that critical temperature is reached. Aluminum was thought to be a good idea because it cools quickly, but alas it also heats up quickly too.
Aluminum does not conduct as well as copper for wires of the same size ( but I would need to make some calculations to tell you how it compares by weight) Your question is good. Aluminum is used extensively for electrical wiring, but copper is preferred for for numerous practical reasons. One of the advantages which aluminum has over copper is cost, but in most cases the economy doesn't compensate for the other drawbacks.
Alluminium has some problems- 1. It has low tensile strength, which makes it suitable only for the wiring with no bending like in long transmission line. 2. Unlike copper it can not be strended many times. Though aluminium is cheaper and lighter for a given current density, it can not be used in household wiring which is subjected numerous bending. It is widely used in transmission, distribution lines and in aircraft.
