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LM31

Aluminium Casting Alloy LM31

This alloy conforms to BS 1490:1988 LM31. Castings are standardised in the as cast (M) condition and in the precipitation treated (TE) condition.

Chemical Composition

	%		%		%
Copper	0.1 max	Magnesium	0.5-0.75	Silicon	0.25 max
Iron	0.5 max	Manganese	0.1 max	Nickel	0.1 max
Zinc	4.8-5.7	Lead	0.05 max	Tin	0.05 max
Titanium	0.25	Chromium	0.4-0.6	Aluminium	Remainder
Others total	0.05 max	Others total	0.15 max

Mechanical Properties

Castings in the as cast (M) condition must be naturally aged for 3 weeks to determine the mechanical properties.

	M Sand Cast	TE Sand Cast
0.2% Proof Stress (N/mm²)	170	-
Tensile Strength (N/mm²)	215	215
Elongation (%)	4	4
Impact resistance Charpy (Nm)	2.7-4.0	-
Brinell Hardness	70	-
Modulus of Elasticity (x103 N/mm²)	71	-
Shear Strength (N/mm²)	180	-

Strength at elevated temperatures

In comparison with the other Aluminium casting alloys, the strength of LM31 at elevated temperatures is good.

Physical Properties


Coefficient of Thermal Expansion (per °C @ 20-100°C)	0.000025
Thermal conductivity (cal/cm²/cm/°C @ 25°C)	0.35
Electrical conductivity (% copper standard @ 20°C)	35
Density (g/cm³)	2.81
Freezing range (°C) approx.	615-570

Machinability

LM31 has good machinability characteristics.

Corrosion Resistance

This alloy has very good corrosion resistance.

Anodising

This alloy is suitable for clear or colour (decorative) anodising.

Heat Treatment

Good Strength and toughness can be produced by natural or artificial ageing after casting. Castings in the as cast (M) condition must be naturally aged for 3 weeks before testing to determine the mechanical properties.

The TE heat treatment condition provides artificial ageing. Using this alloy avoids the risks of distortion and cracking on quenching after solution heat treatment.

Applications and General Notes

LM31 has very good shock resistance and is suitable for shock resisting components. It is used for general engineering castings, particularly large sand casting.