IVD aluminium vacuum coating was originally developed by McDonnell Douglas as a replacement for cadmium treatment of steel and titanium components.
The sequence of the coating process is as follows: First, the parts are degreased to remove cutting or dewatering oils. The next process step is a fine-grained sandblasting. On the one hand, the surface is mechanically cleaned, and on the other hand, a profile with a large surface is produced. The latter supports the physical bonding of the coating to the substrate.
During the process, the parts are held on an electrically conductive frame in a vacuum coating chamber. The parts are moved into the coating chamber, which is evacuated. An inert gas is introduced into the chamber and an electric voltage is applied. This leads to a plasma glow discharge, which is clearly visible as a violet glow in the chamber. The result is a very clean surface on the substrate.
Once this process is completed, the actual coating process can begin. Aluminium wire is now fed to a series of overheated ceramic crucibles. A high voltage is applied to produce very high temperatures and the aluminium evaporates to an electrically charged mist. The negatively charged aluminium atoms move through the vacuum and deposit on the parts to be coated, which are electrically "grounded".
After coating with IVD aluminium, the parts have a dull grey appearance and must be handled with care. The next step is to close the pores in the outer surface of the coating by glass bead blasting. The parts may be used "as plated" or, more frequently, the pure aluminium surface is converted to an aluminium chromate layer by a chemical conversion coating.