Muntz metal (also known as yellow metal) is an alpha-beta brass alloy composed of approximately 60% copper, 40% zinc and a trace of iron. It is named after George Fredrick Muntz, a metal-roller of Birmingham, England, who commercialised the alloy following his patent of 1832.

The alloy must be worked hot and is used today for corrosion-resistant machine parts. Alpha-beta (also called duplex) metals contain both the α and β phases. The α phase refers to a crystal structure that is face-centered cubic, while the β phase is body-centered cubic.

Its original application was as a replacement for copper sheathing on the bottom of boats, as it maintained the anti-fouling abilities of the pure copper at around two thirds of the price. It became the material of choice for this application and Muntz made his fortune. It was found that copper would gradually leach from the alloy in sea water, poisoning any organism that attempted to attach itself to a hull sheathed in the metal. Thus, it was also used to sheathe the piles of piers in tropical seas, as a protection against teredo shipworms, and in locomotive tubes. After successful experimentation with the sheathing Muntz also took out a patent for bolts of the same composition. These too proved a success as they not only were cheaper but also very strong and lasted longer. A notable use of Muntz metal was in the hull of the Cutty Sark.