Chemical impregnation for aluminum casting

Chemical impregnation is a cost effective, permanent solution to the problems that may be encountered as a result of porosity in aluminum castings. Aluminum castings, especially aluminum high pressure die castings, by their nature, contain porosity, which may be too small to be seen, but when permeated by gas or fluid, significant and costly quality problems can arise, even leading to the failure of the aluminum castings in service through leaks or surface defects. Zenith aluminum casting as a professional aluminum foundry, has much experience in handling chemical impregnation for aluminum casting parts.

Porosity types in aluminum die casting parts:

Flow porosity, resulting in surface or internal defects caused by poor pressure conditions in the process.

Gas porosity, usually internal, caused by trapped gases of various kinds in the die. Shrink porosity, the most common and most difficult to control, caused by the change in volume as the metal changes state from liquid to solid.

Vacuum impregnation is the permanent solution to the porosity problem of aluminum casting parts, filling any void with a stable yet flexible material that is resistant to attack from heat, oils or chemicals. The process is sub-surface and can be performed on raw materials or the finished machine part, causing no dimensional change or contamination to the aluminum casting parts.

The process

Before impregnation, porosity within the aluminum castings must be completely clean and dry.


The aluminum casting parts are suspended in a basket before being lowered and immersed in sealant in a pressure autoclave. The vacuum is then released, forcing the sealant deep into the porosity.


The drain cycle involves removing excess sealant from aluminum castings after impregnation. Effective draining is essential to reduce any ‘carry over‘ to the cold wash tank and limit the amount of sealant lost as effluent. The removed sealant is then collected and automatically returned to the autoclave.

Cold Wash

After draining, aluminum castings are transferred to the cold wash tank to remove surface sealant.

Hot Cure

This takes place in a separate tank with water controlled at a minimum of 90°C (195°F). so as to cure the sealant within the porosity and to provide a very effective final washing action for the aluminum casting parts.

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