Aluminium Casting Alloy LM31
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LM31 ALUMINIUM CASTING ALLOY SUMMARY
This alloy complies with BS 1490:1988 LM31. Castings are supplied in the as-cast (M) condition and in the precipitation-treated (TE) state.
CHEMICAL MAKEUP
| % | % | % | |||
|---|---|---|---|---|---|
| Magnesium | 0.4–0.6 | Copper | 1.0–1.5 | Iron | 0.6 max |
| Silicon | 4.5–5.5 | Nickel | 0.25 max | Manganese | 0.5 max |
| Lead | 0.1 max | Zinc | 0.1 max | Titanium | 0.2 max |
| Tin | 0.05 | Other each | 0.05 max | ||
| Others total | 0.15 max | Aluminium | Remainder |
MECHANICAL PERFORMANCE
For castings supplied in the M condition, natural ageing for three weeks is required before mechanical properties can be confirmed.
BEHAVIOUR AT HIGH TEMPERATURES
Compared with other aluminium casting alloys, LM31 offers strong performance at elevated temperatures.
| TB SAND CAST | TB GRAVITY DIE CAST | TF SAND CAST | TF GRAVITY DIE CAST | |
|---|---|---|---|---|
| 0.2% Proof Stress (N/mm²) | 120–140 | 140–150 | 220–280 | 250–300 |
| Tensile Strength (N/mm²) | 170 | 230 | 230–290 | 280–320 |
| Elongation (%) | 2 | 3 | 0–1 | 0–2 |
| Impact Resistance Izod (Nm) | 1.4 | 2.7 | 1.0 | 1.4 |
| Brinell Hardness | 80 | 85 | 100 | 110 |
| Modulus of Elasticity (×10³ N/mm²) | 71 | 71 | 71 | 71 |
| Shear Strength (N/mm²) | - | - | 200 | 235 |
PHYSICAL CHARACTERISTICS
| Coefficient of Thermal Expansion (per °C @ 20–100°C) | 0.000023 |
| Thermal Conductivity (cal/cm²/cm/°C @ 25°C) | 0.34 |
| Electrical Conductivity (% copper standard @ 20°C) | 39 |
| Density (g/cm³) | 2.70 |
| Freezing Range (°C) approx. | 620–550 |
MACHINING QUALITIES
LM31 offers favourable machining characteristics and works well under normal cutting conditions.
RESISTANCE TO CORROSION
This alloy delivers very good corrosion resistance.
ANODISING SUITABILITY
LM31 can be anodised for both clear and coloured (decorative) finishes.
HEAT TREATMENT
Both natural and artificial ageing can produce high strength and good toughness.
Castings in the M condition must be naturally aged for about three weeks before property testing.
The TE condition provides artificial ageing, helping minimise distortion or cracking during quenching after solution heat treatment.
USES AND PRACTICAL NOTES
LM31 offers excellent shock resistance, making it well suited for components subjected to impact. It is widely used for general engineering applications, especially large sand castings.
It is equally suitable for sand casting and for gravity die casting. LM16 has good weldability.