60/40 brass, better known as Muntz metal

From George Frederic Muntz, a Birmingham metal maker who patented the 60/40 alloy in 1832 as a cheaper replacement for the copper sheathing then nailed to the hulls of wooden sailing ships. It did the same job of keeping marine growth and shipworm off the hull, cost about two-thirds as much as copper,. Ship sheathing has long gone, but the name survived, and in Britain the alloy is still sometimes called yellow metal.

Brass with up to about 37 percent zinc is a single alpha phase. Past that point a second phase, beta, starts to form, and at 60/40 the structure is roughly a mix of the two. That is why metallurgists call it a duplex or alpha-beta brass.

The beta phase is harder and less ductile at room temperature, but it becomes very plastic when hot. So the alloy behaves like two materials depending on temperature: soft and forgeable in the furnace, stiff and fairly strong on the bench. This one fact explains almost every use, and every limitation, of 60/40.

Only lightly. It will take bending, light drawing and straightening, and it is supplied as cold-finished rod and tube, but deep cups or multi-stage draws will split it. Within IS 410, the cold-rolled brass sheet standard, CuZn40 is offered only in the O, HB and HD conditions, while 70/30 and 63/37 run the full range up to spring hard. That limited temper range tells you how the alloy behaves. For heavy cold forming use 70/30 cartridge brass instead.

The zinc-rich beta phase is the weak spot. In soft, acidic or chloride-bearing water, and in stagnant seawater, zinc can leach out of the beta grains and leave behind porous copper with almost no strength. The part may look intact until it weeps or snaps. This is called dezincification, and it is the main reason plain 60/40 is not chosen for potable water fittings in aggressive water areas or for long-term seawater immersion.

Where corrosion matters, the usual answers are an alpha brass with arsenic, such as the CuZn30As used in condenser tubes, a dezincification-resistant brass, or a bronze such as phosphor bronze or gun metal.

Despite the dezincification caution, C28000 is one of the alloys listed in ASTM B111 for condenser and heat exchanger tube, and Muntz metal plate has a long history as tube sheet material. In those services the water chemistry is controlled and the thick sections tolerate some surface attack. If your drawing calls for a Muntz tube plate or C28000 tube, send us the size and specification and we will confirm what we can supply.

Buyers sometimes ask for 60/40 rod when they really want free-cutting brass. Free-cutting rod is close to 60/40 in copper but contains 2.5 to 3.5 percent lead, which breaks chips into small pieces and lets the bar run at high speed on an automat. Plain 60/40 has no lead added, so it machines less freely but can be cold headed and brazed without lead causing trouble. If the part is turned, look at our brass rods page for the leaded grades.

Say whether you need hot-rolled plate, cold-finished sheet, extruded or drawn rod, or tube, because the condition changes both the surface and the tolerance. Hot-rolled plate is the usual route for tube sheets and heavy flanges and will need machining to final thickness. Drawn rod and tube come closer to size with a cleaner finish.

Give us thickness or diameter, length, quantity and the specification, whether that is C28000 to an ASTM standard, CuZn40 to IS 410 or the old CZ109. Every lot we supply comes with a test certificate from a Government-recognised test house, so the copper and lead values can be checked before the metal goes into a forge or onto a lathe.