Mix map should work... not in a bump map slot though...
As for the blinn and ward... no... such shading is extremely old legacy workflow, that usually provided quite inferior results.
Metals in Corona are easy... use very dark diffuse values, and high Fresnel IOR values.
For reflectivity amount, do not go all the way to 1, try to stay in 0.5-0.9 range.
For fresnel IOR values... try to stay in range between 4-20 for metals... 4 being rough aluminium and other less reflective metals, 6-8 being brushed steel, 10-15 chrome, and 20 for mirror.
For diffuse value, try to stay really low... like RGB 0-12.
You should be able to achieve convincing metals with these :)