Muntz brass is a copper alloy made using primarily copper (60%), zinc (40%), and traces of iron. As a copper-zinc alloy, it falls under the brasses, and is used frequently by designers seeking an alloy that exhibits the elegant soft golden tone. Muntz metal acquired its name from its inventor, George F. Muntz, who developed the alloy for the lining of boat hulls in 1832. This new brass, 280 brass, maintained the anti-fouling properties of the pure copper sheathing used at the time, but was about 2/3 the cost. It soon became the material of choice for sheathing of boats, piles of piers and locomotive tubes. And it continues to be an excellent choice for marine environments.
Brass 280, sometimes called Yellow Metal, is a form of alpha-beta brass. Alpha-beta brasses – also known as ‘duplex brasses’ or ‘hot-working brasses’ – contain between 37-45% zinc and are made-up of both the alpha grain structure and a beta grain structure. More common than alpha brass, alpha-beta brass is both harder and stronger, and has a lower cold ductility, than alpha brass. Alpha-beta brasses are usually less expensive due to the higher zinc content, but more susceptible to dezincification corrosion. While less workable than alpha brasses at room temperature, alpha-beta brasses are significantly more workable at high temperatures.
Forming 280 Muntz Brass
This alloy falls at the start of the alpha/beta transition, thus its behavior under stresses varies from that of the ductile cartridge brass. It is, however, quite durable. Cold working is possible but difficult. The downside of alpha/beta brasses, is that the alloy will crack under severe cold-working operations. Muntz metal boasts good joining properties, with excellent soldering properties and good brazing and welding using certain methods. However, it is at risk for dezincification corrosion, in which small dark pits appear in the failing metal surface.
When forming, interstitial annealing is required for severe shapes. And the annealing generates oxides on the surface, which are difficult to remove. Under hot-forming operations this alloy performs well. Hot forming will build up oxides on the surface, and discoloration of the surface will require post-polishing – which is why this process is not commonly used for shaping architectural metal features.
Muntz metal can be polished to a mirror finish. Satin polishes and custom polishing are also possible with this striking architectural alloy. Maintaining the color requires either periodic polishing or sealing the material. When used on the exterior of a building, 280 brass sheet should be protected with a clear coating. The bright reflective brass color of Muntz metal will fade, losing reflectivity, and develop over time into a gray-green patina if left to its own devices.
Most Notable Characteristics
- Aesthetically pleasing gold color
- Strong, hard, more rigid than other brass alloys
- Excellent soldering, good brazing and weldability
- Excellent hot working properties, limited cold formability
- Ductile, suitable for hot forging, pressing, and stamping
- Excellent corrosion resistance, withstands marine wear and tear