Zinc aluminium

Zinc-aluminium (ZA) alloys 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 the International Lead Zinc Research Organization (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).[1]

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).[1]

Properties of various zinc aluminium alloys[1]
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 (GPa)] 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
Physical properties Sand cast Permanent mold Sand cast Permanent mold Sand cast Permanent mold
Density [lbm/in3 (g/cm3)] .227 (6.3) 0.227 (6.3) 0.218 (6.0) 0.218 (6.0) 0.181 (5.0) 0.181 (5.0)
Melting Range 375-404°C (707-759°F) 375-404°C (707-759°F) 377-432°C (710-810°F) 377-432°C (710-810°F) 376-484°C (708-903°F) 376-484°C (708-903°F)
Electrical Conductivity [S/m (%IACS)] 1.61 (27.7) 1.61 (27.7) 1.64 (28.3) 1.64 (28.3) 1.72 (29.7) 1.72 (29.7)
Thermal Conductivity [BTU/hr/ft2/°R (W/m/K)] 66.3 (114.7) 66.3 (114.7) 67.1 (116.1) 67.1 (116.1) 72.5 (125.5) 72.5 (125.5)
CTE [68-212°F µin/in/°R (100-200°C µm/m/K)] 12.9 (23.3) 12.9 (23.3) 13.4 (24.2) 13.4 (24.2) 14.4 (26.0) 14.4 (26.0)
Specific Heat [BTU/lbm/°R (J/kg/K)] .104 (435) .104 (435) .107 (448) .107 (448) .125 (523) .125 (523)
Pattern of Die Shrinkage [in/ft (mm/m)] 1/8 (10.4) 1/8 (10.4) 5/32 (13.0) 5/32 (13.0) 5/32 (13.0) 5/32 (13.0)
Chemical Specification (per ASTM) (% by Weight)[1]
ZA8 ZA12 ZA27
Composition Ingot Casting Ingot Casting Ingot Casting
Al 8.2-8.8 8.0-8.8 10.8-11.5 10.5-11.5 25.5-28.0 25.0-28.0
Mg .020-.030 .015-.030 .020-.030 .015-.030 .012-.020 .010-.020
Cu 0.8-1.3 0.8-1.3 0.5-1.2 0.5-1.2 2.0-2.5 2.0-2.5
Fe (max) .065 .075 .065 .075 .072 .075
Pb (max) .005 .006 .005 .006 .005 .006
Cd .005 .006 .005 .006 .005 .006
Sn (max) .002 .003 .002 .003 .002 .003
Ni (other)x10 - - - - - -
Zn Bal Bal Bal Bal Bal Bal
Color Code ASTM B908 Blue Blue Orange Orange Purple Purple

See also

References

  1. 1 2 3 4 "Gravity Casting Alloys". Eastern Alloys, Inc. Retrieved 2007-07-19.

External links

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