Casting Alloys

Casting Alloys

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Midland Pressure Diecasting manufacture die castings for a range of applications in a variety of aluminium and zinc metal alloys. Our technical team can offer recommendations on casting materials which will meet your specifications for die cast product. If there is a specific casting alloy you need please feel free to contact us as we will be able to help with your supply requirements. The following technical descriptions define typically alloys utilised and the information is offered as a guideline only.

Aluminium Alloys

Aluminium alloy die casting contributes the largest percentage of material in die castings today. As the material and process has become better understood throughout the 20th century more and more uses of the material within die castings have developed. Aluminium offers strength properties above those for steel and iron as well as reduced weight which is why automotive is one of the largest industrial sectors with use of aluminium die castings.

Aluminium alloys are well suited to machining and can offer faster and easier machining solutions compared to other materials subject to utilising the ideal machining characteristics. Aluminium alloys compared to steel and cast iron do not suffer from ductile-brittle transformation so can be used in cryogenic applications without any sudden loss in ductility of impact strength. Aluminium is often chosen for it excellent resistance to corrosion, this is in part due to aluminium having a natural oxide film which develops when in contact with air which reforms if damaged, alloys with high content of silicon such as LM6 aid in corrosion protection and use of castings in outdoor environments and the material can also be powder coated, electro-plated or anodised for further corrosion protection.

Aluminium is an easily recyclable material hence its use in many applications.

LM-6

BS Ingot Colour Code: Yellow

LM 6 (BS 1490:1988) – (similar to EN AC/AB 44100/44000, (USA 369.1/A413/B413), (France AS12/13), (Italy UNI4514), Germany (AlSi12, 230), (Japan AC3A))

LM6 (Al-Si12 type) is one of the most widely used aluminium alloys in die cast production. Due to the high silicon content it has excellent fluidity for casting purposes and affords high resistance to corrosion. The alloy provides excellent pressure tightness and hot tearing properties. The material can be machined and care must be taken in utilising the correct tools to minimise wear due to the high silicon content. LM6 is suited to post casting finishing such as powder coating, electro plating and anodising which further enhances its corrosion resistance properties in real world applications.

Alloy composition

Symbol Min % Max %
Magnesium Mg 0.10
Silicon Si 10.0 13.0
Titanium Ti 0.2
Manganese Mn 0.5
Iron Fe 0.6
Nickel Ni 0.1
Copper Cu 0.1
Zinc Zn 0.1
Tin Sn 0.05
Lead Pb 0.1
Others (Total) 0.15
Aluminium Al Remainder

Typical physical and mechanical properties (as cast)

Casting Temperature -725 °C
Freezing Range 565-575 °C
Thermal Conductivity at 25 °C 0.34 cal/cm2/cm/°C
Coefficient of Expansion per °C at 20-100 °C 20 x 10-6
Electrical Conductivity 37% IACS
Density 2.65 g/cm3
0.2% Proof Stress 120 N/mm2
UTS 280 N/mm2
Elongation 2-5%
Hardness 55-60 BHN

LM-24

BS Ingot Colour Code: Red/Blue

LM 24 (BS 1490:1988)– (similar to EN AC/AB 46500, (USA 380/A380/B380), (France AS9U3Z), (Italy G-AlSi8.5Cu), Germany (G-AlSi8Cu3, 226), (Japan AC4B, AD10))

LM24 (Al-Si8Cu3Zn type) is the most widely used aluminium alloy in die cast production together with LM2 they are equally suitable for most applications of die castings. This alloy is highly suited to machining and has better mechanical properties than LM6, its corrosion resistance is good in normal atmospheric conditions and can be further improved via post cast finishing such as powder coating and anodising. It offers excellent pressure tightness and hot tearing properties.

Alloy composition

Symbol Min % Max %
Magnesium Mg 0.30
Silicon Si 7.5 9.5
Titanium Ti 0.2
Manganese Mn 0.5
Iron Fe 1.3
Nickel Ni 0.5
Copper Cu 3.0 4.0
Zinc Zn 3.0
Tin Sn 0.2
Lead Pb 0.3
Others (Total) 0.50
Aluminium Al Remainder

Typical physical and mechanical properties (as cast)

Casting Temperature -700 °C
Freezing Range 520-580 °C
Thermal Conductivity at 25 °C 0.23 cal/cm2/cm/°C
Coefficient of Expansion per °C at 20-100 °C 20 x 10-6
Electrical Conductivity 24% IACS
Density 2.79 g/cm3
0.2% Proof Stress 150 N/mm2
UTS 320 N/mm2
Elongation 1-3%
Hardness 85 BHN

Zinc Alloys

Zinc alloy (also commonly referred to/identified/prefixed as ZL, ZA, Mazak, Zamak) is one of the most widely used materials for die castings in the world. The properties of zinc alloy make the material well suited for die castings required for decorative purposes and functional applications, the economics of zinc die casting are also very favourable. The hardness and dimensional stability of zinc make the material suitable for parts which are required in mechanical assemblies, its thermal and electrical conductivity make it a good choice for electrical component application as well as providing electromagnetic shielding. Zinc alloys (especially the ZA12 alloy) are non-sparking and are suited for applications within hazardous environments such as mines and fossil fuel refineries. Zinc castings are highly versatile for post cast surface finishing and can be made to look like other materials/cosmetically aged via painting and plating as well as other industrial/chemical processes.

Due to the fairly low melting point for zinc compared to other metal alloys there are significant energy savings as well as the reduced impact on the environment. The lower temperatures also mean there is less of a thermal impact on tool steel, therefore providing die life advantages over other casting materials. Zinc is one of the cleanest materials to use for molten processing purposes and is easily recyclable.

ZL-3

BS EN Ingot Colour Code: White/Yellow

ZL 3 (BS EN 1774:1997) – (similar to ZA3, Mazak 3, Zamak 3)

ZL3 is widely used as a general purpose zinc alloy for the hot chamber pressure die casting process. The alloys properties ensure its wide application of uses within the automotive and engineering industries. ZL3 is widely used within the hardware and lock industries as well as for industrial fixings, furniture fittings, toys etc. The chemical composition of ZL3 conforms to the BS EN 1774:1997 standard which is widely standardised across Europe.
ZL3 is suited for machining, polishing, lacquering, powder coating and electro plating – if a high cosmetic plating finish is required zinc is recommended.

Alloy composition

Symbol Min % Max %
Magnesium Mg 0.035 0.06
Aluminium Al 3.8 4.2
Silicon Si 0.02
Iron Fe 0.020
Nickel Ni 0.001
Copper Cu 0.03
Cadmium Cd 0.003
Tin Sn 0.001
Lead Pb 0.003
Zinc Zn Remainder

Typical physical and mechanical properties (as cast)

Casting Temperature 405-425 °C
Freezing Range 382-387 °C
Specific Heat 0.4187 J/gk (0.10)
Solidification Shrinkage 1.17 cm/m (0.14 in/ft)
Casting Shrinkage 0.006 mm/mm (0.006 in/in)
Thermal Conductivity at 18 °C 113 W/m°C (0.27 CGS)
Linear Thermal Expansion per °C 28 x 10-6
Electrical Conductivity at 20 °C 26% IACS
Specific Gravity 6.7
Density 6,700 Kg/m3 (0.24 lb/in3)
Tensile Strength at 20 °C 241-283 N/mm2 (41,000 lbf/in2)
Elongation at 20 °C 10-16% %in 2in
Impact Strength at 20 °C (un-notched) 56.9 J (42 ft.obf)
Hardness 82-87 BHN

ZL-5

BS EN Ingot Colour Code: White/Black

ZL 5 (BS EN 1774:1997) – (similar to ZA5, Mazak 5, Zamak 5)

ZL5 is used within the hot chamber die casting process whereby a stronger alloy than ZL3 is required. It is used where critical dimensional accuracy isn’t too important (don’t forget zinc is easily machined if needed) but strength and hardness is more of a factor in the end product. ZL5 is also suitable where small details in castings is a requirement or where surface preparation for plating using other zinc alloys is an issue. ZL5 is more expensive than ZL3 due to the higher copper content. The chemical composition of ZL5 conforms to the BS EN 1774:1997 standard which is widely standardised across Europe.

ZL5 is suited for machining, polishing, lacquering, powder coating and electro plating – if a high cosmetic plating finish is required zinc is recommended.

Alloy composition

Symbol Min % Max %
Magnesium Mg 0.035 0.06
Aluminium Al 3.8 4.2
Silicon Si 0.02
Iron Fe 0.020
Nickel Ni 0.001
Copper Cu 0.7 1.1
Cadmium Cd 0.003
Tin Sn 0.001
Lead Pb 0.003
Zinc Zn Remainder

Typical physical and mechanical properties (as cast)

Casting Temperature 405-425 °C
Freezing Range 379-388 °C
Specific Heat 0.4187 J/gk (0.10)
Solidification Shrinkage 1.17 cm/m (0.14 in/ft)
Casting Shrinkage 0.006 mm/mm (0.006 in/in)
Thermal Conductivity at 18 °C 108.9 W/m°C (0.26 CGS)
Linear Thermal Expansion per °C 28 x 10-6
Electrical Conductivity at 20 °C 26% IACS
Specific Gravity 6.7
Density 6,700 Kg/m3 (0.24 lb/in3)
Tensile Strength at 20 °C 270-328 N/mm2 (47,000 lbf/in2)
Elongation at 20 °C 7-13% %in 2in
Impact Strength at 20 °C (un-notched) 54-65 J (43 ft.obf)
Hardness 80-92 BHN