The chemical specifications for castings made from the four alloys are shown in the table below. Note that this is the chemical specification for castings. The specification for alloy that the castings are made from is given in EN 1774 Zinc and zinc alloys – Alloys for foundry purposes – Ingot and liquid. This latter specification is tighter to allow a sensible latitude for possible composition variations arising in production.

An overview of chemical specifications for zinc casting alloys can be found in: REF_12_Zinc casting alloys specification

EN 12844 Zinc and Zinc Alloys – Castings – Specifications

Reference 1  

A brief explanation of why the standardised alloying additions and impurity levels are so closely controlled follows:

Both aluminium and copper increase the strength and the hardness of zinc. There are a number of desirable combinations of these three elements that confer properties that are suited to differing situations of application and processing. Three of the alloys are based on these ingredients in different proportions. The remaining alloy, ZP3, is basically a binary zinc aluminium alloy.

Apart from the increase in strength the aluminium content also has two other notable affects. At temperatures below about 450°C it drastically reduces the rate of attack of ferrous materials by the molten alloy. As a result, all zinc aluminium alloys that are castable at temperatures below this level are compatible with the fast and highly productive hot chamber diecasting process.

The other affect of aluminium is to make it essential to avoid contamination of the alloy by elements such as lead, cadmium and tin. Fairly small amounts of these elements can make the alloy vulnerable to intercrystalline corrosion attack especially in warm humid environments. In practice the maintenance of these impurities at low levels and the addition of a small amount of magnesium to the alloy avoids this affect. Magnesium also tends to harden the alloy, but amounts in excess of about 0.1% gives rise to a tendency for castings to crack under the effects of shrinkage stresses whilst still in the die, or due to stresses imposed during ejection from the die.

Iron and nickel form very hard intermetallic compounds with the aluminium content and can lead to problems in machining and finishing of diecastings. If present in sufficient quantity they can reduce the mechanical properties of the alloys, particularly impact strength and elongation. High silicon levels also lead to reduced impact strength. These elements are therefore controlled at low levels.

Reference 2

Equivalent Current National and International Standards

Hot chamber diecasting alloys with almost identical compositions to those in EN 12844 are used outside of the European Union, again alloys equivalent to ZP3 and ZP5 are by far the most commonly used. The most significant of the standard specifications are shown in the table below. If required it is safe to use any of the equivalent specifications below in place of EN12844

Reference 1 and Reference 3

Equivalent European National Standards Existing Prior to 1998

Before 1998 a number of different national standards for zinc alloy diecastings existed across Europe. The table below will help when updating designs created prior to that date.

Reference 1