absorbing microwaves

If you define microwaves as anything above around 1 GHz and below the millimeter wave band (<30 GHz), the answer is no metal at all, because most of the microwave energy is reflected from the metal. The way to use electromagnetic energy to heat metal is at much lower frequencies. Induction welding works at around 150 kHz, but the work piece has to be shaped so that it forms a loop in which eddy currents flow due to the potential induced via Faraday's Law.

GA. You can heat small quantities of metal to melding if you take advantage of shapes. For example, a closed gold trace on a circuit board will melt in a microwave oven (it's not nice to your oven to do this!).

http://en.wikipedia.org/wiki/Susceptor