Relation between Cooling rate and Viscosity in Newtonian fluid

Hi all

I have a situation in the form where i have a molten Aluminium Copper alloy melt poured in a mould
to be solidified. So, the mould temperature is lower than than than the poured melt. I am thinking about a relation which associates temperature or temperature gradient across the fluid in the mould or the cooling rate because of the temperature gradient with the viscosity situation in the melt.
Please suggest expression(s) for the same in such a case.

Best Regards
Ronin