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Aluminium Alloys

Mar 19,2020 | Views: 2552

There is a noticeable trend towards the use of aluminium alloys for medium- to high- volume production in recently years.


The principal advantages of this material are:

1. It costs less than steel.
2. It has good machineabilty: it machines up to 5–10 times faster than steel.
3. Distortion from machining is minimal compared to steel owing to a special heat treatment of the material  during production.
4. The thermal conductivity is excellent, much higher than that of steel, which promotes rapid and efficient heat removal from the mould during moulding.
5. Cavity forms can be made using EDM techniques at a rate of up to six times faster than steel.
6. The weight of aluminium alloys is less than that for comparable sizes of steel.
7. It may be chrome plated or anodised to reduce wear and corrosion.
8. It can be polished and etched in the same way as steel.


The main disadvantages of this material are:

1. The modulus of elasticity is only 30% that of steel.
2. It cannot achieve the same levels of hardness as steel.
3. As it is mechanically weaker than steel, plate thickness’ have to be around 40% greater than with steel.
4. Wear is greater and the material bruises more easily.


The service life of aluminium alloy mould tools can quite readily achieve around 100,000 shots depending on the moulding conditions. There are a few notable exceptions to this where longer service lives of up to a million shots are achieved for straightforward parts, although certain mould parts may have to be replaced because of damage and wear.


There is also an increasing use of hybrid aluminium–steel mould tools in which the advantages of both materials are used to best effect – steel for high-wear areas and aluminium for less critical are as and where high rates of mould cooling are desirable.


Comparison of aluminium with other mould materials


Additional description

Coefficient of

thermal expansion

Thermal conductivity

Density (lb/in3)


Yield strength (KSI)



Aluminium Alcoa 12.8 91 0.102 167 HB 74–79 A
7075-T6 Aluminium 13.1 75 0.101 150 HB 48.73 A
6061-T6 Aluminium 13.1 96 0.098 95 HB 40–42 B
P20 Mold steel 7.1 20 0.284 28–37 Rc 130–135  
S7 Alloy tool steel 6.99 21 0.283 59–61 Rc 210 C
H13 Hotwork die steel 6.1 14.4 0.28 52–54 Rc


420 Stainless steel 5.7 20 0.28 52 Rc 215 C
Beryllium–copper brush Wellman 9.7 60.75 0.302 30–40 Rc 140–155 C
AMPCO Copper Ampco metal 9.7 125 0.315 210 HB 75 D

HB = Brinell hardness; Rc = Rockwell hardness. Higher numbers indicate increased hardness levels. 



A: Moderately weldable, large repairs shoul be avoided.
B: Readily weldable.
C: Moderately weldable, preheat and postweld heat treatment required.
D: Weldable with proper technology.

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