i know copper is better thermal conductor than aluminium but is 0.2mm thick copper better than 1.5mm aluminium at absorbing heat
Depends upon your intended use. Aluminium can dissipate the heat faster, copper can store it longer.
Aluminium is better as the absorber ...
Conducting is not the same as absorbing. To get an answer, you need to be more specific. You should consider the heat capacity of the different materials and, given the different, dimensions, convert to mass. good luck
The copper will be much better at conducting heat across the thickness of the plate. The aluminium will be better at conducting heat along the plate. It depends what you mean by absorbing. The specific heat of aluminium is 2.3 times that of copper. That means that 1.5mm aluminium is 2.3 x (1.5 / 0.2) = 17.25 times better at storing heat than 0.2mm copper.
