The Collaborative International Dictionary of English v.0.48:

manganese bronze \manganese bronze\ n.
   A brass alloy having from 1 to 4 percent of manganese added
   to harden it; made by adding manganese to the copper and zinc
   used in brass.

   Syn: high-strength brass.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

manganese bronze
    n 1: a brass with from 1-4% manganese to harden it [syn:
         manganese bronze, high-strength brass]