Brass Alloys – Cast Alloys

Topics Covered

Introduction

Brasses or copper zinc alloys have excellent corrosion resistance and strength. Brasses are easily cold worked and contain good ductility and strength. Copper zinc alloys with about 35% of zinc are known as single phase alloys that comprise a solid solution of alpha copper and zinc. Alpha alloys are identified by a change in color based on the increase in the content of zinc up to 35%. This increase in zinc results in the production of a stronger elastic brass alloy along with a decrease in corrosion resistance.

A two phase structure is found in brasses comprising zinc content between 32 and 39%. A beta structure is also available with more than 39% of zinc. The two phase brasses can be easily machined and hot worked. The beta phase is generally harder than the alpha phase.

The primary phase in cast alloys is alpha copper containing about 40% of zinc. The beta phase or the high zinc phase is present in areas between the alpha dendrites. The brasses have a microstructure with almost 40% zinc comprising alpha dendrites along with beta surrounding the dendrites. A Widmanstatten structure is formed when the material is cooled slowly resulting in the alpha precipitating out of the solution at the crystal boundaries.

Lead present in the brasses improves the machinability of brass alloys. Increase in the content of lead results in an increase in size and number of globular lead particles.

Applications

The applications of brasses include:

• Piercing
• Coining
• Blanking
• Drawing
• Jewelry
• Fire extinguishers
• Springs
• Lamp fixtures
• Radiator cores
• Flexible hose
• Gold plate bases
• Ammunition

The cast brasses are used in applications that include:

• Fittings
• Low pressure valves
• Architectural trim
• Decorative hardware
• Plumbing fixtures
• Bearings and gears

Composition

The composition of brass alloys is outlined in the following table.

¹Cu + Sum of named elements, 99.1% min.
²In determining Cu min., Cu may be calculated as Cu + Ni.
³Ni value includes Co.
⁴Cu + Sum of named elements, 98.9% min.
⁵Cu + Sum of named elements, 99.5% min.
⁶Includes Co.
⁷Cu + Sum of named elements, 98.7% min.
⁸Cu + Sum of named elements, 99.3% min.