Alloys of Zinc | Metals | Industries | Metallurgy

In this article we will discuss about the die casting and slush casting alloys of zinc.

Die Casting Alloys of Zinc:

In die casting, steel mould is used for casting. The alloy is heated a little above its melting point. Then it is forced into the die by a steel plunger and is kept there under a pressure of 170 kg/cm² or more until solidification takes place. The die being built in two or more parts can be opened.

Composition of Die Casting Alloys:

Aluminium is added to improve strength and ductility of the alloy by reducing grain size. It also reduces the attack of molten metal on dies and other parts of casting machine. Magnesium is added in small quantity as it makes the casting permanently stable.

In these alloys it has been found that corrosion is affected in the following manner:

(a) It is very much accelerated by small quantities of lead and cadmium which are found as impurities in zinc.

(b) It is accelerated by tin.

(c) It is slightly accelerated by nickel and manganese.

(d) Small percentage of copper reduces it.

Zinc alloys for die casting are commonly used because of the following advantages:

(i) Low cost per kg and per casting.

(ii) Can be cast to close dimensions and thus further machining etc., is very much minimised.

(iii) Casting is done very easily. Temperature employed is about 400°C.

(iv) Cost of die material and die redressing is low.

(v) These have got higher strength than other die cast­ing alloys except brass.

(vi) These have sufficient corrosion resistance and ac­cordingly the cost of additional protection is very low.

Slush Casting Alloys of Zinc:

By slush casting process hollow-ware can be produced.

In alloy I, aluminium concentration is not allowed to go very much lower than 5.5% as zinc-aluminium eutectic occurs at 5% aluminium.

These alloys meet following requirements of slush casting alloys:

(i) These have fairly low freezing temperature.

(ii) Solidification occurs over a range of temperature rather than at one definite temperature to produce slushy consistency.