ZA Zinc Alloys
The ZA alloys raise the aluminum in zinc from Zamak’s 4 % to 8, 11 and 27 % with about 1–2 % copper, trading some castability for strength, hardness and bearing performance. ZA-8 still casts hot-chamber at about 290 MPa yield and 375 MPa tensile; ZA-12 (about 320 MPa yield) and ZA-27 (about 370 MPa yield, 425 MPa tensile, 120 HB) are cold-chamber, sand, permanent-mold and continuous-cast alloys that reach the strength of gray iron or leaded bronze at 5.0–6.0 g/cm³. They are the zinc grades that get machined from bar as well as cast — bushings, wear plates, gears and structural brackets.
Popular ZA zinc grades
Compare in the explorerChoose ZA zinc for
Bushings, thrust washers and wear plates replacing leaded bronze; gearbox and pump housings, levers and brackets that would otherwise be gray iron or aluminum; heavy or structural die castings beyond Zamak strength; prototype and short-run gravity castings in sand or graphite molds; and continuous-cast bar for machined bearings and bushings.
Look elsewhere when
The part is small, thin and cosmetic (Zamak 3 or Zamak 7 cast and plate better), it must run above about 120 °C under load (aluminum bronze C954 or gray iron), weight matters (A380 or A356 aluminum are half the density of ZA-8), the bearing runs fast or poorly lubricated (C932 bearing bronze holds up where zinc galls), or the casting must be electroplated to a bright chrome finish — ZA-12 and ZA-27 take plating only with special preparation.
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ZA zinc by application
- Bearings, bushings and wear plates
- ZA-12 continuous-cast bar for general bushings and ZA-27 for high-load, low-speed journals and slides — both replace SAE 660 (C932) bronze at lower density and cost, with good embeddability and no galling against hardened steel if lubricated.
- Structural castings and housings
- ZA-8 in hot-chamber for stronger versions of Zamak parts; ZA-12 and ZA-27 in sand, permanent mold or cold-chamber for gearbox housings, brackets and hand-tool bodies that would otherwise be gray iron.
- Prototype and short-run castings
- ZA-12 poured into graphite or plaster molds gives near-die-cast properties in dozens rather than tens of thousands of parts — the usual way to prototype a Zamak or ZA die casting in the real material.
Working with ZA zinc
- Casting
- ZA-8 runs hot-chamber like Zamak at about 400–420 °C; ZA-12 and ZA-27 are cold-chamber die cast (they attack the hot-chamber gooseneck) or gravity cast in sand, permanent and graphite molds. ZA-27 freezes over a 110 °C range and shrinks about 1.3 %, so it needs generous risers and chills to avoid porosity; ZA-12 is the forgiving one.
- Machining
- All three machine like leaded bronze — fast, with fine finish and low tool wear — using standard carbide or HSS at brass speeds and any light coolant. ZA-12 and ZA-27 bar is turned into bushings and thrust washers as a matter of routine; ZA-27 is slightly harder on tools because of its 120 HB hardness and higher aluminum content.
- Heat treatment and stability
- Not hardenable, but ZA-27 castings are given a stabilizing treatment (about 320 °C for 3 h, furnace-cooled) to complete a phase transformation that would otherwise cause slow dimensional growth and a small strength loss in service; ZA-8 and ZA-12 are used as cast. Keep sustained service below about 120 °C — the ZA alloys creep less than Zamak but still creep.
- Finishing
- ZA-8 electroplates like Zamak with a copper strike; ZA-12 and especially ZA-27 need a zincate or special activation because the aluminum-rich surface passivates, so they are usually painted, powder-coated, chromated or left bare for bearing duty. Chemical conversion coats and e-coat adhere well on all three.
Other zinc alloy series
ZA Zinc Alloys — frequently asked
What is ZA zinc?
The ZA alloys raise the aluminum in zinc from Zamak’s 4 % to 8, 11 and 27 % with about 1–2 % copper, trading some castability for strength, hardness and bearing performance. ZA-8 still casts hot-chamber at about 290 MPa yield and 375 MPa tensile; ZA-12 (about 320 MPa yield) and ZA-27 (about 370 MPa yield, 425 MPa tensile, 120 HB) are cold-chamber, sand, permanent-mold and continuous-cast alloys that reach the strength of gray iron or leaded bronze at 5.0–6.0 g/cm³. They are the zinc grades that get machined from bar as well as cast — bushings, wear plates, gears and structural brackets.
Which grade of ZA zinc should I use?
ZA-8 when a Zamak part needs more strength, hardness or creep resistance without leaving the hot-chamber process: about 30 % stronger than Zamak 3, the best creep of any hot-chamber zinc, and it plates almost as well. ZA-12 is the general-purpose gravity and cold-chamber alloy — sand, permanent-mold and graphite-mold castings and continuous-cast bar for bushings — with the best balance of strength, castability and bearing properties. ZA-27 for the highest strength and the lightest zinc (5.0 g/cm³) in pressure die castings and heavy sand castings, and for bearings under high load and low speed where it outperforms SAE 660 bronze; it needs careful feeding, benefits from a stabilizing heat treatment at about 320 °C, and is the hardest of the three to plate.
Which grade of ZA zinc is the strongest?
ZA-27 has the highest yield strength in the series at 370 MPa; ZA-8 follows at 290 MPa. Values are for each grade's default condition.
Which grade of ZA zinc is easiest to machine?
ZA-8 (machinability very good, 80/100), then ZA-12 (80/100).
Is ZA zinc heat-treatable?
No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.
ZA-8 or Zamak 5 for a stronger hot-chamber casting?
Zamak 5 is the smaller step — about 15 % over Zamak 3 with identical casting and plating behaviour. ZA-8 is the larger one: about 290 MPa yield and 375 MPa tensile against roughly 270 and 330 for Zamak 5, hardness over 100 HB and markedly better creep, still in the same hot-chamber machine. The price is a slightly higher melt temperature, a touch less fluidity for the thinnest walls, a little lower ductility and a bit more effort to plate. Pick Zamak 5 when the part must plate bright and only needs a margin; ZA-8 when the part carries sustained load, threads or press fits.
Can ZA-12 or ZA-27 really replace bronze bearings?
For high-load, low- to moderate-speed journals, slides and thrust washers with lubrication — presses, agricultural and mining machinery, jigs — yes: ZA-27 carries higher static loads than SAE 660 (C932) bronze, ZA-12 runs at similar loads with better embeddability, and both weigh about a third less and machine faster from continuous-cast bar. They lose to bronze when the bearing runs hot (above about 120 °C zinc softens and creeps), fast (PV limits are lower), or dry, and they are not a replacement for hardened steel or aluminum bronze in heavily loaded gears.