Beware of the white heat sink compound. There is a widespread mistaken impression that the stuff improves heat transfer between metal objects. The truth is, it is better than air. It was originally intended to improve the thermal transfer between semiconductors and heat sinks. If the surfaces of both had been machined perfectly, there would have been no use for the goo. The approved use is not to slather it on, just apply the least possible and spread well. It then fills the air gaps left by minor imperfections.
The advantage of aluminium over copper is cost and weight. Copper has a better thermal performance, but is heavier and usually more expensive, also when cooling coils were first being mooted, there was a world shortage of copper, and why many houses got galvanised plumbing and cables all over the country were made from aluminium.