LM4 is a general-purpose aluminium casting alloy with about 5% silicon and 3% copper. It casts well in sand and gravity dies, machines cleanly, and can be heat treated for higher strength. It is used for pump bodies, gearbox housings, motor covers, brackets and general engineering castings.
Quick facts
- Type
- Aluminium-silicon-copper casting alloy
- Silicon
- About 4–6%
- Copper
- About 2–4%
- Tensile strength
- About 140–280 MPa, depending on casting and heat treatment
- Castability
- Good
- Machinability
- Good
Equivalent grades
| Standard | Grade |
|---|---|
| BS 1490 | LM4 |
| EN 1706 | AC-45000 (AlSi6Cu4, close) |
| IS 617 | 4225 (close) |
| ASTM | 319 (close) |
Equivalents are close, not identical. Name the grade and standard on the drawing.
Typical chemical composition
| Element | % |
|---|---|
| Silicon (Si) | About 4–6 |
| Copper (Cu) | About 2–4 |
| Iron (Fe) | Up to 0.8 |
| Manganese (Mn) | About 0.2–0.6 |
| Zinc (Zn) | Up to 0.5 |
Values are typical. The exact limits depend on the standard and supplier; ask for the mill test certificate when it matters.
LM4, LM6 or LM25?
| LM4 | LM6 | LM25 | |
|---|---|---|---|
| Strength | Medium, higher when heat treated | Lower | High when heat treated |
| Corrosion resistance | Fair (contains copper) | Excellent | Good |
| Castability | Good | Excellent | Good |
| Typical use | Housings, pump bodies | Thin, complex, marine parts | Automotive, stressed parts |
Typical uses
- Pump and valve bodies
- Gearbox and motor housings
- Brackets and covers
- Manifolds
- General engineering castings
Need parts made in LM4 aluminium alloy?
Post your requirement free. Workshops that take your kind of work see it and get in touch. You only talk to the ones that fit.
Get startedRelated
Related job work
Questions
- Can LM4 be heat treated?
- Yes. LM4-TF (solution treated and aged) is noticeably stronger and harder than as-cast LM4-M.
- Is LM4 good for outdoor or marine use?
- It has fair corrosion resistance because of its copper. LM6 is preferred for marine and wet service, or LM4 is painted or powder coated.
- Is LM4 easy to machine?
- Yes, it machines cleanly with sharp carbide or HSS tools and gives a good finish.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 22 October 2026.