Why do most radiators use a mixed material of copper and aluminum?

At this point, some people may come to the conclusion that 'copper is definitely better than aluminum'. But you will find that the vast majority of heat sinks are made of a mixture of copper and aluminum, and there are also pure copper ones, but very few. Is it a matter of cost? The cost of copper is about three times more expensive than aluminum, and manufacturers mix copper and aluminum to save money?
It's not actually a matter of cost, after all, CPU heat sinks are relatively inexpensive compared to other computer accessories. Even if they are made of pure copper, how expensive can they be?
The reason for using a mixed material of copper and aluminum is that we cannot simply judge the effectiveness of a heat sink based on specific heat. Specific heat needs to be compared under the premise that the two metals have the same weight. The density of copper and aluminum is completely different, which means that they have different volumes under the same weight, so the heat dissipation area is also different. For example, if 100g of copper and aluminum are used to make a heat sink, the area made of aluminum will definitely be larger than that of copper.
So we need to take volume into consideration and replace specific heat with heat capacity. The density of copper (8.9) is more than three times higher than that of aluminum (2.7), so the specific heat needs to be multiplied by the density to calculate the heat capacity. The result of the multiplication is: the heat capacity of copper is 3.43 J/Gv; The heat capacity of aluminum is 2.42 J/Gv. That is to say, aluminum is more likely to cool down at the same volume.
Copper conducts heat three times faster than aluminum, but at the same volume, aluminum has a cooling efficiency 1.5 times higher than copper. So they each play to their own advantages, using copper with faster thermal conductivity to make the base in contact with the CPU, which conducts heat quickly; Aluminum, which cools down faster, is used to make radiator fins to quickly remove heat.