Copper Alloys

Introduction

A wide variety of copper alloys are available for use in construction. The variations in color stem primarily from differences in chemical composition. Production and forming methods may affect alloy selection. Additional information is available upon request. The CDA publication Copper Brass Bronze - Architectural Applications covers the selection process in greater detail.

Technically, alloys primarily of copper and tin are considered bronzes, while those chiefly of copper and zinc are brasses. In practice, however, the term bronze is commonly used for a variety of copper alloys, including those with little or no tin. This is because they resemble true bronzes in both natural and weathered colors. Table 1.3.1 lists the characteristics of some of the more popular copper alloys and their common names.

A Unified Numbering System has been developed for metals and alloys by ASTM and SAE. CDA administers the section on copper and its alloys. This system is based on wrought alloy numbers ranging from C10000 through C79999. Cast alloy numbers range between C80000 and C99999.

Nickel-silver alloys C74500 and C79600 are usually called "white bronze"; all others are considered "yellow bronze". "Statuary bronze" and "green bronze" do not refer to specific alloys, but to their naturally weathered or chemically induced colors. The former is used to describe brown to black surfaces; the latter is used for patinas.

In general, most copper alloys eventually weather to the gray-green patina. There are, however, significant variations in their natural colors and in the rate at which they form a patina. The last two columns in Table 1.3.1 contain information about the natural and weathered colors of the alloys. Table 1.3.2 is a color matching table. It depicts which alloys, in various forms, are reasonably well matched in color with the sheet, strip, and plate copper alloys.

Back to Top

Copper Alloy Table

Table 1.3.1 Common Copper Alloys
AlloyCommon TermCompositionColor
NaturalWeathered
C11000 / C12500 Copper 99.90% Copper Salmon Red Reddish-Brown to Gray-Green Patina
C12200 Copper 99.90% Copper
0.02% Phosphorous
Salmon Red Reddish-Brown to Gray-Green Patina
C22000 Commercial Bronze 90% Copper
10% Zinc
Red Gold Brown to Gray-Green Patina in Six Years
C23000 Red Brass 85% Copper
15% Zinc
Reddish Yellow Chocolate Brown to Gray-Green Patina
C26000 Cartridge Brass 70% Copper
30% Zinc
Yellow Yellowish, Gray-Green
C28000 Muntz Metal 60% Copper
40% Zinc
Reddish Yellow Red-Brown to Gray-Brown
C38500 Architectural Bronze 57% Copper
3% Lead
40% Zinc
Reddish Yellow Russet Brown to Dark Brown
C65500 Silicon Bronze 97% Copper
3% Silicon
Reddish Old Gold Russet Brown to finely mottled Gray-Brown
C74500 Nickel Silver 65% Copper
25% Zinc
10% Nickel
Warm Silver Gray-Brown to finely mottled Gray-Green
C79600 Leaded Nickel Silver 45% Copper
42% Zinc
10% Nickel
2% Manganese
1% Lead
Warm Silver Gray-Brown to finely mottled Gray-Green
Back to Top

Color Matching Chart

Table 1.3.2 Color Matching Chart
Forms to be Matched in Color
Sheet and Plate AlloysExtrusionsCastingsFastenersTube& PipeRod & WireFiller Metals
C11000 / C12500
Copper
C11000 / C12500
(simple shapes)
Copper
(99.9% Min.)
C65100
Low Silicon
Bronze
C12200 C11000 / C12500 C18900 Copper
C12200
Copper
C11000 / C12500
(simple shapes)
Copper
(99.9% Min.)
C65100
Low Silicon
Bronze
C12200 C11000 / C12500 C18900 Copper
C22000
Commercial Bronze,
90%
C31400 Leaded
Commercial Bronze
C83400 C65100
Low Silicon
Bronze
C22000 C22000 C65500
C23000
Red Brass,
95%
C38500
Architectural Bronze
C83600 C28000
C65100
Low Silicon
Bronze
C23000 C23000 C65500
C26000
Cartridge Brass,
70%
C26000
(simple shapes)
C85200,
C85300
C26000,
C36000,
C46400,
C46500
C26000 C26000 C68100 Low
Fuming Bronze
C28000
Muntz Metal
C38500
Architectural Bronze
C85500,
C85700
C28000
C65100
Low Silicon
Bronze
C23000 C28000 C68100 Low
Fuming Bronze
C65500
High Silicon Bronze
C65500
(simple shapes)
C87500 C65100,
C65500
C65100,
C65500
C65100,
C65500
C65500
C74500
Nickel-Silver
C79600 Leaded
Nickel-Silver
C97300 C74500 C74500 C74500 C77300
Back to Top

Forming

Numerous methods can be used to form copper alloys into sheet, plate, rod, wire, and irregular shapes. Table 1.3.3 indicates forming methods appropriate for use with common alloys. The following is a brief description of each method:

Bending: A mechanical forming process performed at room or at elevated temperatures. Bending is accomplished with the aid of rollers, bending shoes and mandrels. Its primary purpose is to produce curved sections from straight lengths of tube, rod, or extruded shapes.

Brake Forming: A mechanical bending operation usually performed on metal sheet, strip, or plate.

Castings: These are produced by pouring molten metal into a mold and allowing it to cool and solidify. This method is used to form irregular shapes. Only specially formulated alloys C80000 through C99999 can be cast.

Explosive Forming: A high energy rate forming method by which shapes are produced using only a single die. The energy is supplied by chemical explosives. Large shapes can be formed without the need for heavy equipment.

Extrusion: The process of producing a metal shape of constant cross-section by forcing the heated metal through an appropriately shaped die. In general, cross-section diagonals should not exceed six inches. The average thickness of copper alloy extrusions should be about 1/8 inch. The resulting shape can be almost any length, limited mostly by the structural requirements of the final object.

Cold Forging: A forming process in which a metal object at room temperature is shaped by repeated hammering.

Hot Forging: A method of forming metal objects in which a heated slug or blank cut from wrought material is pressed into a closed cell impression die.

Hydroforming: A forming process in which a sheet alloy is pressed between a male die and a rubber piece subjected to hydraulic pressure.

Laminating: Bonding of sheet or strip alloys to various substrates such as steel, plywood, aluminum, or rigid insulating material. The bond is typically achieved with the use of adhesives. The resulting panel can be quite strong, even with thin copper alloy material.

Roll Forming: Shapes made from sheet or strip material by passing it between multiple stands of contoured rolls. Generally, the corners are not as sharp as those achieved by extrusion.

Spinning: A mechanical forming process in which sheet or strip alloy is shaped under pressure applied by a smooth hand tool or roller while the material is revolved rapidly.

Stamping: Shaping sheet or strip alloy by means of a die in a press or power hammer.

Back to Top

Forming Chart

Table 1.3.3 Forming Methods
Forming MethodAlloys C11000 / C12500C12200C22000C23000C26000C28000C38500C65100C65500C74500C77400C79600
Bending + + + + + + + + +
Brake Forming + + + + + + + +
Casting All Alloys C80000 - C99999
Explosive Forming + + + + + + + +
Extrusion + + +
Cold Forging + + + + + +
Hot Forging + + + + + + +
Hydroforming + + + + + + + +
Laminating All Copper Sheet and Strip Alloys
Roll Forming + + + + + + +
Spinning + + + + +
Stamping + + + + + + +
Back to Top

Joining

Mechanical fasteners, such as screws, bolts, and rivets provide the simplest and most common joining technique. They typically do not require specialized tools for installation, and many can be removed for disassembly. Table 1.3.2 lists the companion fasteners for each sheet or plate alloy by simplifying color matching and reducing the risk of material incompatibility.

Adhesives can also be used in certain applications. The lamination process of a sheet alloy onto a substrate is dependent on adhesive bonding. Relatively thin sheet alloys can be bonded to steel, plywood, aluminum, or certain types of foam, which act as rigid insulation. The strength and rigidity of the resulting composite panel is often achieved by the combined section acting as one unit.

The integrity of the bond is dependent on surface preparation, adhesive selection, bonding procedure, and joint design. Laminated panels for exterior applications should use a thermosetting or high quality thermoplastic adhesive. Edges and joints are the most vulnerable areas on a panel, as they are the most likely entry points for moisture.

There are three commonly used metallurgical methods for joining alloys: soldering, brazing, and welding. Table 1.3.4 summarizes the joining characteristics of each alloy for these methods.

Where the joining material is required mostly for watertightness, soldering may be used. Lead or tin-based filler metals with melting temperatures below 500 degrees Fahrenheit are typically used. Soldered joints typically depend on mechanical fasteners for strength. This method is commonly used for sealing joints in gutter, roofing, and flashing applications. Since the filler material does not match copper alloys in color, soldering should only be used in concealed joints when appearance is critical.

Brazing is the preferred metallurgical method for joining pipe and tube copper alloys. Two metal sections are joined with a non-ferrous filler material with a melting point above 800 degrees Fahrenheit, but below the melting point of the base metals. Blind or concealed joints are recommended, since the color match of silver filler material is fair to poor. Where this is not possible, mechanical removal of excess material may be necessary.

The final metallurgical joining method, welding, is seldom used with copper alloys because of problems with joint distortion and color matching. Welding uses high temperature or pressure to fuse the base metals together, often with an additional filler metal. Silicon bronzes are the only copper alloys which can be readily welded.

Back to Top

Joining Chart

Table 1.3.4 Metallurgical Joining Characteristics
Joining MethodAlloys C11000 / C12500C12200C22000C23000C26000C28000C38500C65100C65500C74500C79600
Brazing G E E E E E G E E E G
Soldering E E E E E E E E G E E
Welding
Oxyacetylene NR G G G G G NR G G G NR
Gas Shielded Arc F E G G F F NR E E F NR
Coated Metal Arc NR NR NR NR NR NR NR F F NR NR
Spot Resistance NR NR NR F G G NR E E G NR
Seam Resistance NR NR NR NR NR NR NR G E F NR
Butt Resistance G G G G G G F E E G F
E = Excellent G = Good F = Fair NR = Not Recommended
Back to Top

Finishes

There are three generic categories of finishes for copper alloys: mechanical treatments, chemical treatments and coatings. Designations for these finishes were originally developed by the National Association of Architectural Metal Manufacturers. The chemical treatments and coatings available for copper alloys are basically similar to those for copper, see Finishes for more information.

Alloy Color Chart

Mechanical treatments are finishes that are typically applied at the shop by mechanical means. They usually affect only the surface of the alloy. There are five standard mechanical designated finishes:

As Fabricated: This is the finish of the alloy at the completion of its production process, such as rolling, extrusion, or casting.

Buffed: Alloys with this type of finish require grinding, polishing, and buffing. They usually have a specular or smooth specular, mirror-like appearance, which is the brightest mechanical finish available.

Directional Textured: Wheel or belt polishing with fine aggregates is required for this finish. The result is a continuous pattern of very fine, nearly parallel scratches. There are six standard variations available: fine satin, medium satin, coarse satin, uniform, hand rubbed and brushed.

Non-directional Textured: This matte finish is primarily used on castings. Sand or metal shot is sprayed under high pressure to achieve a certain degree of roughness. Clear protective coatings are often used to maintain the original appearance.

Patterned: A process in which a copper alloy sheet is pressed between two rolls to produce a pattern. When both rolls have matching engraved patterns they emboss the sheet with the pattern visible on both sides. Otherwise, when only one roll has a pattern and the other is smooth, the pattern is impressed into one side of the sheet, a process called coining.

Back to Top