Thermal Conductivity of Aluminium

Commercially pure aluminium conducts a little over half as well as copper but at a third of the density, so per unit of mass it is the better conductor: the reason heat sinks, radiators and overhead transmission conductors are aluminium. The alloying penalty is severe and routinely overlooked: 6061-T6, the structural workhorse, manages only about 167 W/(m·K) by NASA's data handbook, and the stronger alloys less still. Extruded heat sinks are usually 6063, chosen partly because it keeps more of the pure metal's conductivity.

Temper matters too, because it changes how much solute is in solution versus precipitated: 6061 in the T4 temper conducts less than in T6. Take 212 as commercially pure metal at room temperature and use the alloy datasheet for anything real. In fin design the conductivity mostly sets the fin efficiency: beyond a certain thickness-to-length ratio, extra conductivity buys almost nothing, and the convective film coefficient is what limits the heat sink.