Aluminium Die Casting Alloy LM24
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LM24 ALUMINIUM DIE-CASTING ALLOY SUMMARY
This alloy meets the BS 1490:1988 LM24 specification.
CHEMICAL MAKEUP
| % | % | % | |||
|---|---|---|---|---|---|
| Copper | 3.0–4.0 | Magnesium | 0.3 max | Silicon | 7.5–9.5 max |
| Iron | 1.3 max | Manganese | 0.5 max | Nickel | 0.5 max |
| Zinc | 3.0 max | Lead | 0.3 max | Tin | 0.2 max |
| Titanium | 0.2 max | Aluminium | Remainder | Others: each | 0.50 max |
MECHANICAL PERFORMANCE OF LM24 DIE-CASTINGS
| GRAVITY DIE CAST | HIGH PRESSURE DIECASTING | |
|---|---|---|
| 0.2% Proof Stress (N/mm²) | 100–120 | 150 |
| Tensile Strength (N/mm²) | 180 | 320 |
| Elongation (%) | 1.5 | 1–3 |
| Impact Resistance Izod (Nm) | - | 3.4 |
| Brinell Hardness | 85 | 85 |
| Modulus of Elasticity (×10³ N/mm²) | 71 | 71 |
| Shear Strength (N/mm²) | - | 185 |
BEHAVIOUR AT HIGH TEMPERATURES
Tensile strength at room temperature remains mostly stable up to around 150°C, but drops to roughly half its value once temperatures reach about 250°C. Note that other limitations may also affect die-casting performance at elevated temperatures.
PHYSICAL CHARACTERISTICS OF LM24 DIE-CASTINGS
| Coefficient of Thermal Expansion (per °C @ 20–100°C) | 0.000021 |
| Thermal Conductivity (cal/cm²/cm/°C @ 25°C) | 0.23 |
| Electrical Conductivity (% copper standard @ 20°C) | 24 |
| Density (g/cm³) | 2.79 |
| Freezing Range (°C) approx. | 580–520 |
MACHINING QUALITIES
Machining behaviour is similar to other silicon-bearing aluminium casting alloys. However, unlike high-silicon grades such as LM6, LM24 does not exhibit severe drag during cutting. Tool wear is still relatively rapid. Carbide-tipped tools are recommended to achieve a good finish, though well-sharpened high-speed steel tools can also be used. Lower-grade steels may be acceptable if frequently resharpened. Lubricant and coolant should always be employed.
RESISTANCE TO CORROSION
Corrosion performance under standard atmospheric exposure is comparable to LM4—generally good. In marine or other harsh conditions, castings should be protected with paint.
ANODISING SUITABILITY
Chromic or sulphuric acid anodising can produce a grey protective film. However, pressure die-cast surfaces in this alloy are usually not ideal for decorative anodising. If the component is intended for corrosive environments, anodising becomes necessary.
USES AND PRACTICAL NOTES
LM24 is primarily a pressure die-casting alloy with excellent flow characteristics. It is easier to die-cast than high-silicon aluminium alloys and is widely used for engineering components requiring good mechanical strength.
It is often preferred over LM6 for pressure die-casting when corrosion resistance is not the dominant requirement. LM24 offers good brazability and weldability.
For most die-casting applications, LM2 and LM24 can be used interchangeably. LM24 is typically supplied in a non-heat-treated condition.