T6 Heat Treatment for A356 Aluminum Gravity Castings

Due to the high fluidity and good castability, A356 aluminum alloy is the common material used in gravity die casting process to creat cast aluminum parts in near net shape.

A356 is one of the most common aluminium alloys used to obtain near net shape Aluminum gravity castings made of A356 aluminum alloy can achieve many benefits including good wear and corrosion resistance, hot tearing resistance, good weldability and high strength to weight ratio. Cast aluminum A356 alloy belongs to a group of hypoeutectic Al-Si alloys, so A356 aluminum castings are widely used in the automotive and avionics industries.

T6 Heat Treatment

T6 Heat Treatment for A356 Aluminum Gravity Castings

T6 Heat Treatment is a two-phase process which is applied to aluminum castings to increase the strength of the alloy by as much as 30%.

To achieve T6 temper, the process consists of three steps:

  • Solution Treatment: Heat the casting to ~1000 F for several hours
  • Quenching: Drastically cool part in a water bath
  • Artificial aging: Reheat the part a final time at ~300-400 F

T6 heat treatment will precipitate the alloying elements of A356 aluminum gravity castings in the form of fine coherent particles of Mg2Si and Al2Cu inside the grains during the aging stage to harden the alloy. The long duration solution heat treatment is able to alter the morphology of the Si phase into spheroidal shape and hence change the properties of the aluminium alloy. Kindly remind that T6 heat treatment could only be operated for aluminum gravity die castings becaused of its low cost.

After T6 heat treatment, the mechanical properties of A356 aluminum gravity die castings will be changed as below:

Hardness: Testing is performed to check the hardness after heat-treated A356 aluminum gravity die castings. To be more accurate, several tests are taken to get the average hardness value. It is noted that the hardness is increased 106% after applying T6 heat treatment.

Tensile strength: Two tensile test samples are subjected to test and the averaged values are taken to plot the ultimate tensile strength. The non-heat-treated A356 sample achieves a tensile strength of 123.0 MPa while T6 heat-treatment A356 one improves it tremendously to 253.5 MPa, 106% improvement. Heat-treatment is found to be very effective to improve the tensile strength of A356 gravity die castings.

Besides, the elongation and fatigue are also improved after heat treatment. Typical A356 cast aluminum parts with T6 heat treatment are: skateboard truck hanger & baseplate, exhaust manifold, etc.

Conculsion

T6 heat-treatment is able to improve the mechanical properties of gravity die-cast A356 parts. The hardness, tensile strength and elongation are improved to the greatest extent of 106 and 214%, respectively. As a professional aluminum foundry in China, we are able to deal with both A356 aluminum casting and T6 heat treatment. Any inquiry on aluminum casting with T6 heat treatment, pls feel free to contact our foundry!

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