Aluminium LM4 Alloy Ingots for General Castings

LM4 is a general engineering casting alloy. The silicon gives it reasonable fluidity and keeps shrinkage manageable; the copper gives strength and makes it free machining. The result is an alloy that suits medium-sized castings of moderate complexity, where the part will be machined and will carry some load.

Typical castings are pump and valve bodies, compressor and gearbox housings, inlet manifolds, motor housings and end covers, electrical fittings, pulleys and general machine parts. Pump makers, motor manufacturers and automotive component suppliers all buy it for these parts.

Yes, and that is one of its main advantages over LM6. The copper content lets LM4 respond to precipitation hardening. In BS 1490 terms, LM4-M is the as-cast condition and LM4-TF is fully heat treated: solution treated, quenched and then artificially aged.

Fully heat treated LM4 roughly doubles its as-cast tensile strength in chill castings, at the cost of ductility. If a design calls for LM4-TF, tell your heat treater the casting method, as sand and chill castings respond slightly differently, and remember that the properties in the table are for separately cast test bars, not for every section of a real casting.

LM4 has a wide freezing range compared with LM6, which makes it more prone to shrinkage porosity in thick sections and heavy junctions. Good feeding with risers and chills matters. It is suitable for sand casting and gravity die casting, and it is used for some pressure die castings too.

The copper also means LM4 is less corrosion resistant than the low-copper alloys. It is fine for most indoor, oil-wetted and general outdoor parts, but for seawater, marine fittings or food contact many designers choose LM6 instead. Pressure-tightness is moderate; for leak-tested castings, LM6 or a properly fed LM4 casting with impregnation is common.

Gravity die castings in LM4 come out with a finer grain and better properties than sand castings, which is why the chill-cast figures in the table are higher. If you are converting a part from sand to gravity die, expect to revisit gating and feeding rather than simply pouring the same alloy into a metal mould.

Charge clean, dry ingots and preheat them at the furnace before adding to a molten heel. Degas the melt to remove hydrogen, which otherwise shows up as gas porosity. Keep returns, gates and risers segregated by alloy; LM4 scrap mixed into an LM6 melt will push copper over the LM6 limit of 0.1 percent, and that cannot be undone.

Do not overheat the melt. Extra temperature increases hydrogen pickup and oxide formation without improving casting quality. Iron pickup from bare steel tools and crucibles should be avoided too, since iron forms brittle needle-shaped compounds; coat ladles and stirrers.

Ingot certificates for LM4 should report silicon, copper, magnesium, iron, manganese, nickel, zinc, lead and tin against the BS 1490 or IS 617 limits. Jubilant Impex supplies LM4 ingots with a test certificate through a Government-recognised test house. For the rest of our foundry metals, see the ingots page, and for machining-shop context, our engineering and machining page.