Aluminium alloys in sand casting

Aluminium alloys in sand casting

At Haworth Castings, aluminium alloys are often our material of choice due to their unique physical and mechanical properties.

The most widely used aluminium alloys are LM25 and LM6. The ‘LM’ prefix is a standardised industry code given to the alloy to reflect the varying chemical constituents and trace elements, such as magnesium, copper and zinc.

Here we take a look at the main alloys used at our foundry:

LM6

This high silicon-based alloy has excellent corrosion resistance so it is suited to both land and marine casting applications. LM6 is very ductile and less brittle than some metals. It is ideal for intricate and thin sections and also for large castings.

Main applications: marine, automotive and road transport parts, the chemical and dyeing industries (for pump parts), paints, and castings for the food and domestic product markets.

LM25

This aluminium alloy has excellent mechanical properties and it is used where high strength is required. The strength can be further increased through heat treatment. LM25 also offers good corrosion resistance and weldability, as well as better machinability than LM6.

Main applications: the marine, electrical, aviation, food, chemical and nuclear energy industries. This alloy is often used for road transport parts, such as cylinder blocks and heads, and other engine and body castings.

Chemical composition of LM6 and LM25

All as % LM6 LM25
Copper 0.10 max 0.20 max
Magnesium 0.10 max 0.20 – 0.6 max
Silicon 10.0 – 13.0 max 6.5 – 7.5 max
Iron 0.6 max 0.5 max
Manganese 0.5 max 0.3 max
Nickel 0.1 max 0.1 max
Zinc 0.1 max 0.1 max
Lead 0.1 max 0.1 max
Tin 0.05 max 0.05 max
Titanium 0.2 max 0.2 max
Aluminium Remainder Remainder

Other alloys

In addition to LM6 and LM25, we also use:

BSL169 – this is primary aluminium extracted directly from the main aluminium ore, bauxite. This material has better elongation (stretch) than LM25 and it is used on many high-specification MOD applications.

LM13 – commonly used in aerospace applications since it offers good wearability in high temperature environments.

L119 – offers a particularly high resistance to heat. It is used in a whole host of applications, from turbines to train engines.

LM31 – offers excellent mechanical properties and strength at high temperature. This strength can be produced through natural age hardening; heat treatment is not necessarily needed. LM31 also offers good corrosion, shock and wear resistance. It is used for general engineering components, particularly large sand castings.

Selecting an alloy

Aluminium alloys in sand casting

The choice of alloy is driven by our customer requirements and the specific end applications for the casting.

Whichever material is selected, our dedicated foundry engineers take great care to keep the aluminium alloys segregated prior to the metal pour, which is vital to ensure that there is no cross-contamination of different materials.

Our engineers use specialist spectrographic techniques to check the chemical constituents of each metal pour before the casting process begins. They can finely tune the trace elements if any adjustments are required.

If you would like further information about our aluminium sand casting, gravity-die casting or finishing processes, please email us today at: sales@haworthcastings.co.uk or call +44 (0)1794 512685.