Engine blocks Materials

K.G.Maheswaran

Required Material Properties• High strength

Diesel engines-High strength is a concern (As CR >17)

• High Modulus of elasticity

• High Abrasion resistance

• High Corrosion resistance

– Should also have a • Low density,

• Low thermal expansion (to resist expanding under high operating temperatures)

• Low Thermal conductivity (to prevent failure under high temperatures)

• Good machinability and castability

• Good vibration damping (to absorb the shuddering of the moving parts)

• Required mechanical properties for a typical aluminum engine block

• Ultimate tensile strength of 245 Mpa

• Yield stress of 215 Mpa

• Fatigue strength of 60 MPa

Engine blocks Materials

• Constitutes 20-25% of the total weight of an engine

• Cast iron alloys-Early engine blocks were manufactured from primarily due to its high strength and low cost

• Aluminum alloys-Used sparingly in the 1930’s

• Increased during the 1960’s and 1970’s

• Aluminum alloys increase fuel efficiency and performance.

• Magnesium alloy-AMC-SC1-weighs less than both cast iron and aluminum alloys

• Diesel engine blocks-compacted graphite cast iron (CGI)-alternative to gray cast iron

Gray cast iron alloys

• Gray cast iron alloys typically contains

• 2.5-4 wt.% Carbon

• 1-3 wt.% Silicon• 1-3 wt.% Silicon

• 0.2-1.0 wt.% Manganese

• 0.02-0.25 wt.% Sulfur

• 0.02-1.0 wt.% Phosphorus

Gray cast iron alloys -Properties

• Excellent damping capacity,

• Good wear and temperature resistance,

• Easily machinable, and is inexpensive to produceproduce

• But are relatively weak and are prone to fracture and deformation

Compacted Graphite Cast Iron

• Higher tensile strength and elastic modulus than gray cast iron

• Good damping capacity and thermal conductivity,

• Difficulty to machine

• 150,000 Ford/Peugeot’s diesel

Aluminum Alloys

• ADV:

• Improved performance-to-weight ratio and increased fuel efficiency

• DISADV:• DISADV:

• More expensive to manufacture THAN Cast iron alloys

• NOW Cost IS Decreased

Aluminum Alloys CompositionAluminum alloy 319

• 85.8-91.5 wt.% Aluminum• 5.5-6.5 wt.% Silicon,• 3-4 wt.% Copper• Maximum 0.35 wt.% Nickel• Maximum 0.35 wt.% Nickel• Maximum 0.25 wt.% Titanium• Maximum 0.5 wt.% Manganese,• Maximum 1% Iron,• Maximum 0.1 wt.% Magnesium• Maximum 1 wt.% Zinc

Aluminum Alloys Properties

• Good casting characteristics

• Good corrosion resistance

• Good Thermal conductivity

Aluminum alloy A356

• 91.1-93.3 wt.% Aluminum

• 6.5-7.5 wt.% Silicon

• 0.25-0.45 wt.% Magnesium• 0.25-0.45 wt.% Magnesium

• maxima of 0.2 wt.% Copper

• 0.2 wt.% Titanium

• 0.2 wt.% Iron

• 0.1 wt.% Zinc

Magnesium AlloysUsed as

• Valve covers

• Cylinder head covers

• Intake manifolds • Intake manifolds

• Rocker arm covers

• Air intake adaptors

• Induction systems

• Accessory drive brackets

Sand-cast AMC-SC1 magnesium alloy

• This grade of magnesium alloy contains two rare earth elements,lanthanum and cerium, and was heat-treated with T6.

Other properties of the magnesium alloy

• Good thermal conductivity,

• Excellent machining and casting qualities,

• Excellent damping characteristics

Auto bodies: Some, such as Audi and Jaguar are now using aluminium (5xxx series alloys).

Steel is still the main metal with a mixture of HSLA steel Steel is still the main metal with a mixture of HSLA steel (high stength, low alloy), TRIP (transformation induced plasticity) and rephosophorised types - these are almost exclusively galvanised or galvanealed.

speeds requires a low reciprocating mass

• Crank shaft (car and bike) These tend to be forged from low alloy chromium-molybdenum steel (sometimes chromium-moly-vanadium).

• Some of these will be nitrided to improve fatigue resistance (depends on manufacturer).

• Piston This is a tricky one. There has been a move towards piston crowns being made of hyper-eutectic aluminium-silicon alloys for petrol (gasoline) engines. While some diesels have aluminium crowns (with oil injection underneath to keep the crown cool), some are still based on low alloy steel.

• Bike engines are almost exclusively aluminium as the high engine

Con-rods With the exception of the ultra-trick titanium rods on some very highly stressed engines (bike racing mainly), these are also low alloy steels of the same type as the crank.

Cylinder blocks are nearly all aluminium now.

BMW have developed a magnesium block with a seperateBMW have developed a magnesium block with a seperatecast-in aluminium cylinder casting.

Ford, Toyota, Peugeot/Citreon, Land-Rover all use cast iron cylinder liners in an aluminium block (some pushed in, some cast in). BMW and VAG use aluminium liners in (mainly) aluminium blocks