LM25
Aluminium Casting Alloy (AL - Si7Mg0.5)
Colour Code - Yellow / Blue
Chemical composition (Blue Figures - EN 1706 AC-42000) Copper 0.2 Max 0.2 (0.15) Magnesium 0.2 - 0.6 0.20 - 0.65 Silicon 6.5 - 7.5 6.5 - 7.5 Iron 0.5 Max 0.55 (0.45) Manganese 0.3 Max 0.35 Nickel 0.1 Max 0.15 Zinc 0.1 Max 0.15 Lead 0.1 Max 0.15 Tin 0.05 Max 0.05 Titanium 0.2 Max 0.05 - 0.25 Aluminium Remainder
Mechanical Properties LM25-M   Sand Cast Chill Cast 0.2 % Proof Stress ( N/mm2)* 80 - 100 80 - 100 Tensile Stress ( N/mm2)* 130 - 150 160 - 200 Elongation ( % )* 2 3 Impact Resistance. Izod (Nm) 9.0 4.0 Brinell Hardness Number 55 - 65 55 - 65 Modulus of Elasticity (x103 N/mm2) 71 71         Mechanical Properties LM25-TE   Sand Cast Chill Cast 0.2 % Proof Stress ( N/mm2)* 120 - 150 130 - 200 Tensile Stress ( N/mm2)* 150 - 180 190 - 250 Elongation ( % )* 1 2 Impact Resistance. Izod (Nm) 70 - 75 75 - 95 Brinell Hardness Number 55 80 - 110 Endurance Limit ( 5 x 107 cycles +/- N/mm2) 71 71 Modulus of Elasticity (x103 N/mm2) 140         Mechanical Properties LM25-TB7   Sand Cast Chill Cast 0.2 % Proof Stress ( N/mm2)* 80 - 110 90 - 110 Tensile Stress ( N/mm2)* 160 230 Elongation ( % )* 2.5 5 Brinell Hardness Number 65 - 75 65 - 75 Endurance Limit (5x108 cycles;N/mm2) 70 - 100 75 Modulus of Elasticity (x103 N/mm2) 71 71       Mechanical Properties LM25-TF   Sand Cast Chill Cast 0.2 % Proof Stress ( N/mm2)* 200 - 250 220 - 260 Tensile Stress ( N/mm2)* 230 - 280 280 - 320 Elongation ( % )*   2 Brinell Hardness Number 90 - 110 90 - 110 Endurance Limit (5x108 cycles;N/mm2) 60 95 Modulus of Elasticity (x103 N/mm2) 71 71 Shear Strength (N/mm2) 180 205
Strength at Elevated Temperatures. The tensile properties of LM25 alloy at elevated temperatures are influenced by the condition (Heat Treatment) of the castings and the duration at the elevated temperature. On short term testing (30 Mins) the properties fall only slowly and uniformly up to about 200 deg C, at which the strength of LM25 - TF is reduced by about 20%. Very prolonged heating (10,000 Hours) results in a sharp loss of strength at around 135 deg C. At 200 deg C the strength of LM 25 - TF is less than half of that at room temperature. There is therefore no advantage to be gained by heat treatment if the component is to be used at elevated temperatures above 130 deg C for extended periods.
Physical Properties Coefficient of thermal Expansion. (per degree Centigrade at 20 - 30 ºC.) 0.0000022 Thermal Conductivity. ( Cal / cm2 / cm / ºC / sec at 20 ºC) 0.36 Elecrical Conductivity ( % Copper Standard at 20 ºC) 39 Specific Gravity 2.68 Freezing Range ( ºC ) approx. 555 - 615 Figure for conductivity applies to Diecastings. Values are approximate and will vary with condition.
Machinability The heat treated alloy has fairly good machining properties, but tools should preferably be of high speed steel and must be kept sharp. A moderately high rate of tool wear may be expected. Liberal cutting lubricant should be employed.
Corrosion Resistance Resistance to corrosive attack by sea water and marine atmospheres is high.
Anodising A protective anodic film can be obtained by either the sulphuric or chromic acid process, but the grey opaque character of the coatings of normal thickness precludes their colouring in light shades for decorative purposes.
Casting Characteristics FLUIDITY - Good, suitable for fairly thin castings. PRESSURE TIGHTNESS- Excellent, suitable for leak-tight castings. HOT-TEARING - Excellent, problems due to hot tearing are very rare. TYPICAL POURING TEMPERATURE - 710 deg C. Practical pouring temperatures will depend on the mould configuration. Care must be taken not to over-heat the melt, or Magnesium may be lost resulting in poor properties. Care with Clorination must also be taken to avoid removing Magnesium.
Heat Treatment There are three levels of heat treatment conditions commonly used for LM25. LM25 - TE (Precipitation treated) - Heat for 8 - 10 Hours at 155 - 175 deg C and air cool. LM25 - TB7 (Solution treated and stabilised) - Heat for 4 - 12 Hours at 525 - 545 deg C and quench in hot water, then stabilise at 250 deg C for 2 - 4 Hours. The time at temperature must be long enough to ensure a reasonable stability of the properties prior to mechanical testing. LM25 - TF (Fully heat treated) - Heat for 4 - 12 Hours at 525 - 545 deg C and quench in hot water. Precipitation treat for 8 - 12 Hours at 155 - 175 deg C.
Applications and General Notes LM25 is mainly used where good mechanical properties are required in castings of shape or dimensions requiring an alloy of excellent castability in order to achieve the desired standard of soundness. The alloy is also used where resistance to corrosion is an important consideration, particularly where high strength is also required. it has good weldability. Consequently LM25 finds applications in the food, chemical, marine, electrical and many other industries, and above all - in the automotive industry where it is used for wheels, cylinder blocks and heads. It's potential uses are increased by it's 4 available levels of heat treatment in both sand and chill castings. It is, in practice, the general purpose high strength gravity diecasting alloy. LM25 may be superior for castings, particularly in chill moulds, which are difficult to make to the required standard of soundness. It offers better machinability and mechanical properties than LM6.
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