As Dr. Bad Science Ben Goldacre says, "I think you'll find it's a bit more complicated than that." It's not hard to dig up solar spectral power density data - which depends heavily on latitude and season, of course -- but how a "metal" sheet behaves depends on tons of parameters.
Different metals (elemental or mixtures) have different spectral absorptivities as well as specific heat (how much energy per unit volume per unit temperature change). Further, for example, a roughened surface may have a higher net absorption.
In summary, you'll need a lot more specific info, including sheet thickness.
In the shade, any material will reach thermal equilibrium with the local atmosphere.