Die Casting Alloys Used in Industries: 5 Types | Metallurgy

The following points highlight the five main types of die casting alloys used in industries. The types are: 1. Zinc-Alloys 2. Aluminium-Alloys 3. Copper Base Alloys 4. Magnesium Base Alloys 5. Lead and Tin Base Alloys. 

Type # 1. Zinc-Alloys:

They are most widely used as die casting alloys (as over 75% of die castings produced are zinc base).

The typical composition of zinc base alloys is given below.

Aluminium = 4.1%, Copper = 0.1% (1.0% max.), Magnesium = 0.4%, Zinc = Remainder.

The advantages are as follows:

(i) They permit longer die life since they are easily die cast at lower temperature.

(ii) Relatively high strength can be obtained in zinc alloys. Tensile strength is of the order of 300 kg/cm².

(iii) At usual casting temperatures, zinc-alloys provide very good fluidity and thus permit casting of very thin sec­tions.

Zinc die castings are widely used in automotive industry, oil burners, refrigerators, radio, television, machine tools, business machines, etc.

Type # 2. Aluminium-Alloys:

These are very popular especially in cold chamber application as molten alloys of aluminium will stick to steel, if kept in continuous contact.

The typical composition of this alloy is as follows:

Copper = 3 to 3.5%, Silicon = 5 to 11%, Magnesium = 0.5%, Aluminium = Remainder.

(a) They are among the lightest alloys and hence castings obtained are lighter in weight.

(b) Aluminium alloys have good corrosion resistance along with relatively low melting temperatures of about 650°C.

(c) The chilling action of the dies promotes a fine grained structure, which improves the mechanical proper­ties of the alloys. Tensile strength is of the order of 1250 to 2500 kg/cm².

(d) These castings have good machinability and sur­face finish.

Type # 3. Copper Base Alloys:

In this category, brass and bronze are most commonly used and these present a problem in pressure casting because of their high casting temperature (800 to 1000°C).

The typical composition of copper base alloy is given below:

Copper = 57 to 81%, Zinc = 15 to 40%, Silicon = 1 to 4%, Lead = 1.5%, Tin = 1.5%.

The characteristics of copper base alloys are given below:

(1) Very high tensile strength (from 3700 to 6700 kg/ cm²) along with good corrosion resistance.

(2) They are resistant to wear.

(3) As the fluidity is quite low, therefore, high temperatures are needed which reduce the life of die.

Copper base alloys are mostly used for electrical- machinery parts, small gears, marine, air-craft and automotive fittings, chemical apparatus and miscellaneous hardware etc.

Type # 4. Magnesium Base Alloys:

These are the lightest in die-cast alloys, being about 2/3rd the weight of alloys of aluminium. The cost of production is slightly higher than aluminium but is compensated against the light weight. These alloys are cast in the same fashion as aluminium base alloys and are best suited for cold chamber machines.

The typical composition of magnesium base alloys is as given below:

Aluminium = 9%, Zinc = 0.5%, Manganese = 0.5%, Silicon = 0.5% (Max.), Copper = 0.3%, Magnesium = Remainder.

Because of lightness and good machinability, they are mostly used for aircraft industry, motor and instrument parts, portable tools and household appliances, etc.

Type # 5. Lead and Tin Base Alloys:

These alloys have limited applications in die-casting, because of toxic effect upon the workers. The tensile strength of these alloy castings is of the order of 600 kg/cm².

The typical composition of lead base alloys is given below:

 

They are most widely used for light duty bearings, battery parts, X-ray shields, low cost jewellery and in non- corrosive metal applications.