C355-T61 Aluminum Alloy

C355-T61 is an alloy of aluminum used for casting. It contains copper as well as magnesium and silicon as alloying elements. The combination of alloying elements in C355 create a metal that ranks among the highest in strength and elasticity for aluminum casting alloys. It also has superior performance at elevated temperatures. Because of this C355 is considered superior to the A356 alloy used commonly in aluminum casting applications. The C355 alloy Dart uses is pure virgin aluminum and does not contain secondary, or scrap aluminum that can introduce contaminants like sand to the alloy.

The T61 classification refers to the heat treatment process used on the alloy, which plays an important role in determining the final properties of the resultant metal.

Dart cast aluminum blocks and heads are manufactured exclusively from virgin C355-T61 alloy.

Mechanical Properties of Aluminum Alloys
	Ultimate			Brinell	Copper
Material	Tensile	Yield	Elongation	Hardness	Content
C355-T6	39	29	5%	85	1.30%
C355-T61	46	43	3%	90-115	1.30%
356-T6	30	20	3%	55-90	0.30%
A356-T6	34	24	3%	70-105	0.30%
357-T6	45	36	3%	85-115	0.10%

Ultimate Tensile Strength: Expressed in kpsi (thousand pounds per square inch). The ultimate tensile strength of a metal is the maximum stress that it can withstand before the material tears apart - a catastophic failure.

Yield Strength: Also expressed in kpsi. Yield strength is the stress that a material can withstand without becoming permanently deformed. In a high performance engine, a part must have high yield strength to perform properly under heavy loads.

Elongation: When a material is tested for tensile strength it elongates a certain amount before fracture takes place. The two pieces are placed together and the amount of extension is measured against marks made before starting the test. This measurement is expressed as a percentage of the original gauge length.

Brinell Hardness: Expressed in the Brinall scale. The industry standard measurement of a material's hardness. Hardness directly affects the wear resistance of a part.

Copper Content: Expressed as a percentage. The copper content of the alloy directly affects the material's performance at elevated temperatures.

Thermal Properties: One of the chief benefits of the 355 aluminum alloy in a racing engine is that it maintains it's strength at higher temperatures than 356-type alloys. A 356 aluminum begins to degrade in strength at appoximately 200 degrees F, while C355 aluminum is not affected until it reaches temperatures of around 300 degrees F, this differential can be critical in a highly stressed racing engine.

C355-T61 Aluminum Block and Cylinder Head

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