Zinc aluminium
Encyclopedia
Zinc-aluminium alloy
s are alloys whose main constituents are zinc
and aluminium
. Other alloying elements include magnesium
and copper
. This type of alloy was originally developed for gravity casting. Noranda, New Jersey Zinc Co. Ltd., St. Joe Mineral Co. and ILZRO were the main companies that pioneered the ZA alloys between the 1950s and the 1970s. They were designed to compete with bronze
, cast iron
and aluminium using sand
and permanent mold
casting methods. Distinguishing features of ZA alloys include high as-cast strength, excellent bearing properties, as well as low energy requirements (for melting).
ZA alloys make good bearings because their final composition includes hard eutectic zinc-aluminium-copper particles embedded in a softer zinc-aluminium matrix. The hard particles provide a low-friction bearing surface, while the softer material wears back to provide space for lubricant to flow, similar to Babbitt metal
.
The numbers associated with the name represent the amount of aluminium in the alloy (i.e. ZA8 has 8% aluminium).
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s are alloys whose main constituents are zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
. Other alloying elements include magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
and copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
. This type of alloy was originally developed for gravity casting. Noranda, New Jersey Zinc Co. Ltd., St. Joe Mineral Co. and ILZRO were the main companies that pioneered the ZA alloys between the 1950s and the 1970s. They were designed to compete with bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
, cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
and aluminium using sand
Sand casting
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material.It is relatively cheap and sufficiently refractory even for steel foundry use. A suitable bonding agent is mixed or occurs with the sand...
and permanent mold
Permanent mold casting
Permanent mold casting is metal casting process that employs reusable molds , usually made from metal. The most common process uses gravity to fill the mold, however gas pressure or a vacuum are also used. A variation on the typical gravity casting process, called slush casting, produces hollow...
casting methods. Distinguishing features of ZA alloys include high as-cast strength, excellent bearing properties, as well as low energy requirements (for melting).
ZA alloys make good bearings because their final composition includes hard eutectic zinc-aluminium-copper particles embedded in a softer zinc-aluminium matrix. The hard particles provide a low-friction bearing surface, while the softer material wears back to provide space for lubricant to flow, similar to Babbitt metal
Babbitt metal
Babbitt, also called Babbitt metal or bearing metal, is any of several alloys used for the bearing surface in a plain bearing.The original Babbitt metal was invented in 1839 by Isaac Babbitt in Taunton, Massachusetts, USA. Other formulations were later developed...
.
The numbers associated with the name represent the amount of aluminium in the alloy (i.e. ZA8 has 8% aluminium).
| ZA8 | ZA12 | ZA27 | ||||
|---|---|---|---|---|---|---|
| Mechanical properties | Sand cast | Permanent mold | Sand cast | Permanent mold | Sand cast | Permanent mold |
| Ultimate tensile strength [ksi (MPa)] | 38 (263) | 32-37 (221-255) | 40-46 (276-317) | 45-50 (310-345) | 58-64 (400-441) | 45-47 (310-324) |
| Yield strength - 0.2% offset [ksi (MPa)] | 29 (200) | 30 (206) | 31 (214) | 39 (269) | 54 (372) | 37 (255) |
| Elongation [% in 2"] | 1-2 | 1-2 | 1-3 | 1-3 | 3-6 | 8-11 |
| Shear strength [ksi (MPa)] | - | 35 (241) | 37 (255) | - | 42 (290) | 33 (228) |
| Hardness [Brinell] | 85 | 85-90 | 89-105 | 89-105 | 110-120 | 90-110 |
| Impact strength [ft·lbf (J)] | 156 (20) | - | 193 (25) | - | 353 (47) | 433 (58) |
| Fatigue strength rotary bend in 5x108 cycles [ksi (MPa)] | - | 7.5 (52) | 15 (103) | - | 25 (172) | 15 (103) |
| Compressive yield strength 0.1% offset [ksi (MPa)] | 29 (199) | 31 (214) | 33 (227) | 34 (234) | 48 (331) | 37 (255) |
| Modulus of elasticity [psi x 106 (MPa x 103)] | 12.4 (85.5) | 12.47 (85.5) | 12.07 (82.7) | 12.07 (82.7) | 11.37 (77.9) | 11.37 (77.9) |
| Poisson's ratio | 0.29 | 0.29 | 0.30 | 0.30 | 0.32 | 0.32 |