Zinc and Zinc Alloys

خلاصات:

Chemical specifications for zinc casting alloys are given in ASTM B86 for No. 2, No. 3, No. 5 and No. 7 alloys and ASTM B791 for ZA-8, ZA-12 and ZA-27.

Alloys covered by B86 are hypo-eutectic (i.e. they contain less aluminum than the eutectic chemistry of 5% Al) with a composition close to 4% Al. Alloys included in B791 are hypereutectic with an aluminum content greater than the eutectic chemistry. All of the zinc casting alloys have dendritic/eutectic microstructures, however, the hypoeutectic alloys solidify with zinc-rich dendrites, whereas hypereutectic alloys solidify with aluminum-rich dendrites.

Chemical specifications for zinc casting alloys are given in ASTM B86 for No. 2, No. 3, No. 5 and No. 7 alloys and ASTM B791 for ZA-8, ZA-12 and ZA-27.

Alloys covered by B86 are hypo-eutectic (i.e. they contain less aluminum than the eutectic chemistry of 5% Al) with a composition close to 4% Al. Alloys included in B791 are hypereutectic with an aluminum content greater than the eutectic chemistry. All of the zinc casting alloys have dendritic/eutectic microstructures, however, the hypoeutectic alloys solidify with zinc-rich dendrites, whereas hypereutectic alloys solidify with aluminum-rich dendrites.

The mechanical and physical properties of the castings, and to a lesser extent their corrosion properties, are closely linked to the specific alloy type, the casting process and quality of the castings produced, the amount of ageing or service life of a component casting and the level of impurities, amongst others.

Both Cu and Mg increase strength properties, reduce ductility and inhibit intergranular corrosion. Iron is present as small FeAl3 particles and does not influence mechanical properties unless it exceeds 0,1%. When limited to the specified amounts shown in ASTM B86 and B791 Pb, Sn and Cd do not cause intergranular corrosion or the lowering of physical and mechanical properties. Other impurity elements such as Cr, Ni, Mn, Ti, Sb, In, As, Bi and Hg do not normally occur in sufficient quantities in zinc casting alloys to be of concern.

Gravity Casting Alloys

A recent alloy development is generation of a family of zinc foundry alloys suitable for sand, permanent mold, plaster mold, shell mold and investment casting. Many of these alloys also can be die cast in cold chamber machines where strength and/or hardness beyond the properties of AG41A are required. Currently, two alloys are finding increasing application, a 12%-Al alloy (ILZRO 12) and a 27%-Al alloy (Zn-27Al). These two gravity casting zinc alloys have been designed for structural applications and should not be confused with die casting and slush casting alloys, which often are used for decorative gravity cast parts.

The mechanical properties of these zinc alloys make them attractive substitutes for cast iron and copper alloys in many structural and pressure-tight applications. Because zinc is less costly than copper, these zinc alloys have a distinct cost advantage over copper-base alloys. The ease of machining of zinc and its inherent corrosion resistance give it advantages over cast iron.

Zinc gravity casting alloys have attractive foundry properties. Due to their low melting temperatures (below 540°C) and casting temperatures, energy requirements are low. They are readily cast in thin sections - less than 2,5 mm in sand molds. Melting and casting of these alloys are virtually pollution free. No fluxing or degassing is required, and because of the low casting temperatures minimal pollution from the sand mold results.

The 12%- Al alloy is preferred for heavy sections and is suitable for permanent mold casting in both metal and graphite molds. Its permanent mold casting characteristics are similar to those of aluminum permanent mold alloys. The 27%-Al alloy should be specified when higher mechanical properties are required in thin section sand castings. Care should be taken to prevent hot spots in the mold, which contribute to underside shrinkage.

Zinc gravity casting alloys can be used for general industrial applications where strength, hardness, wear resistance or good pressure tightness is required. Zinc alloys often are employed to replace cast iron because of their similar properties and higher machinability ratings. The good bearing and wear characteristics of zinc alloys permit them to be used for bearing bushings and flanges. Other applications in which zinc alloys have been successfully substituted for cast iron or copper alloys include fuel-handling components, pulleys, electrical fittings and hardware components.

Wrought Zinc and Zinc Alloys

Wrought zinc and zinc alloys may be obtained as rolled strip, sheet and foil; extruded rod and shapes; and drawn rod and wire. These metals exhibit good resistance to corrosion in many types of service, and because the corrosion products that may form on them are white, other materials are not stained by them.

Wrought zinc has chemical characteristics particularly adapted to certain uses, such as dry batteries and photoengraver`s plate, and offers combinations of desirable physical and mechanical properties at relatively low cost. In common with many other metals and alloys, wrought zinc creeps under constant loads that are substantially less than its ultimate strength; that is, wrought zinc does not have clearly defined elastic module, and hence creep data from service tests must be used in designing for strength and rigidity under conditions of continuos stress.

All severe fabrication of wrought zinc should be done at temperatures above 20°C. Rolled zinc of the proper grade is readily drawn into a great variety of articles such as batter cups, eyelets, meter cases, novelties, flashlight reflectors and fruit-jar caps. Suitable grades of rolled zinc also are readily rolled, press formed, stamped or spun into items such as plates for addressing machines, buckles, ferrules, ornaments, nameplates, gaskets, weather-stripping and lamp parts.

The ordinary grades of wrought zinc can be soldered easily by conventional methods. The usual precautions should be observed regarding proper cleaning and fluxing. The metal must not be overheated to the point where it melts. Pulsed-arc welding may be used for joining; gas welding of zinc is used only for repair work.

Wrought zinc is easily machined using standard methods and tools. However, if it is necessary to machine zinc containing exceedingly coarse grains, the metal should be heated to a temperature between 70 and 100°C in order to avoid cleavage of crystals.

In general the same methods are used for finishing wrought zinc and zinc alloys as are used for finishing zinc-base die castings. However, in bake-enameling of wrought zinc, greater caution should be exercised in avoiding temperatures high enough to impair mechanical properties. For this reason air-dried finishes are preferable.

ابحث في قاعدة معلومات

ادخل عبارة لتبحث عنها:

بحث بِـ:

الوثيقة الكاملة
الكلمات المفاتيح

ترويسات
خلاصات

Physical properties are available for a huge number of materials in the Total Materia database.

Data is available through official information from standards and also through Total Materia unique similar materials cross referencing functionality, adding another dimension to your search for physical properties data!

Enter the material of interest into the quick search field. You can optionally narrow your search by specifying the country/standard of choice in the designated field and then clicking "Search".


After selecting the material of interest to you, click on the Physical Properties link to view data for the selected material. The number of physical property data records is displayed in brackets next to the link.


Physical properties are displayed according to the origin of the data set. Official data from standards can be found under the official tab, data deriving from other sources for the material will also be displayed under its own tab.


The similar materials tab displays all materials that are similar to the original material and have physical properties inserted. This can be very handy when looking for equivalent materials!


The typical tab gives a generic overview of property data for the material for you to use as a useful starting point for further investigation.


For you’re a chance to take a test drive of the Total Materia database, we invite you to join a community of over 150,000 registered users through the Total Materia Free Demo.