LM6 vs LM25 vs LM24 Aluminum Alloy, What Are The Differences?

When selecting an aluminum alloy for a casting application, understanding the varying properties of specific graded materials is vital. Three alloys regularly considered for their castability and mechanical attributes are LM6, LM25, and LM24. While all are in the LM series designation standard, each offers distinct characteristics influencing their suitability for different fabrication needs. This article provides the differences between aluminum LM6, LM25, and LM24.

What’s Aluminum Alloy LM6

LM6 has a chemical composition of 10-13% silicon, with smaller amounts of other elements like copper, magnesium, iron, manganese, and nickel. It is suited for die casting processes like sand casting, pressure die casting, and gravity die casting. Mechanical properties include a tensile strength of 160-190 MPa for sand casting and 280 MPa for pressure die casting, with an elongation of 5% for sand casting and 2-5% for pressure die casting. Its strength decreases at temperatures above 250°C. LM6 exhibits excellent corrosion resistance under atmospheric and marine conditions and can be anodized in various colors. It is widely used for marine components, automobile fittings, housings, and other applications where ease of casting and corrosion resistance are important. However, it has relatively low machinability due to its silicon content.

What’s Aluminum Alloy LM25?

LM25 is an aluminum casting alloy that conforms to British Standard BS 1490:1988. It has a chemical composition of 0.2% maximum copper and 0.2-0.6% magnesium, with 6.5-7.5% silicon. LM25 can be produced through sand casting, gravity die casting, and high pressure die casting processes. It exhibits higher strength levels than other aluminum alloys when heat treated, with the precipitation treated (TE) condition, solution treated and stabilized (TB7) condition, and fully heat treated (TF) condition offering increasing mechanical property improvements. Some key properties include a tensile strength of 160-200 MPa in the as-cast condition increasing to 220-260 MPa when fully heat treated. LM25 also displays good corrosion resistance and machinability. It finds wide application in automotive components, transportation, industrial machinery, and other situations where higher strength combined with ease of casting is required.

What’s Aluminum Alloy LM24?

LM24 is an aluminum alloy that conforms to British Standard BS 1490:1988. It has a chemical composition containing 3.0-4.0% copper, 0.3% maximum magnesium, and 7.5-9.5% maximum silicon, and can be used for both gravity die casting and high pressure diecasting processes. Mechanical properties include a tensile strength of 180 MPa for gravity die castings and 320 MPa for high pressure diecast parts, with retention of most room temperature strength up to around 150°C. Machinability is similar to other aluminum alloys containing silicon, requiring carbide tools. Corrosion resistance is fair under normal conditions but protection is needed in marine environments. LM24 principally provides excellent casting characteristics for pressure die casting applications and higher mechanical properties than LM6 in die cast components, making it well-suited for high strength die casting applications.

Difference Between LM6, LM25 & LM24

	LM6	LM25	LM24
Composition	0.1% max Cu	0.2-0.6% Mg	3.0-4.0% Cu
Strength	Moderate	High, enhanced by heat treatment	High for die casting
Machinability	Difficult, high Si	Fair	Similar to other Al-Si alloys
Heat Treatment	Generally not	Can be strengthened through precipitation hardening	Generally not
Corrosion Resistance	Excellent	Good	Fair, needs protection in marine environments
Casting Process	Sand, die casting	Sand, gravity die casting	Die casting
Applications	Marine, auto fittings	General fabrication, transportation	High strength pressure die casting