ZINC
CASTING PROCESS COMPATIBILITY Zinc alloys are most often diecast, a process in which mol-
ten metal is injected into metal molds under high pressure. The alloys also can be cast in sand molds, plaster molds or graphite permanent molds to produce prototypes.
DESIGN CONSIDERATIONS • Intersections of features, such as walls, ribs and gussets, should blend with transition sections and generous radii.
• Draft angles may be minimized where metal content is critical, such as thin sections oriented parallel to die draw. Casting to zero draft may be specifi ed in some cases to eliminate fi nish machining operations.
• Sharp exterior corners can be specifi ed on appearance sur- faces, otherwise they should be broken with radii or chambers to reduce die maintenance.
PROCESSING CONSIDERATIONS • Zinc alloys readily accept a deco- rative bright or wear-resistant hard-chrome fi nish via electro-
plating for improved corrosion resistance.
• Zinc alloys can be painted easily and eco- nomically, and the color match with sheet steel is excellent.
• Chromate treatments are applied to zinc alloys to develop a decorative finish or as a base for paint and corrosion protection.
Typical Mechanical Properties of Common Alloys Alloy
Ultimate Strength (ksi)
Zinc Alloy 2 Zinc Alloy 3 Zinc Alloy 5 Zinc Alloy 7 ZA-8 ZA-12 ZA-27
48 35 39 41
43 45 52
- - - -
32 35 46
Yield Strength (ksi)
Elongation %
2
16 13 18
20 10 3
Hardness Bhn
98 72 80 67 91 91
100 Source: Engineering Properties of Zinc Alloys, International Leaded Zinc Research Organization
Zinc’s surface fi nish makes it a good candidate for plating and painting.
Jul/Aug 2012 | METAL CASTING DESIGN & PURCHASING | 37
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