The Altim TD treatment for aluminium surface treatment

Citation

(2001), "The Altim TD treatment for aluminium surface treatment", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 3. https://doi.org/10.1108/aeat.2001.12773cad.014

The Altim TD treatment for aluminium surface treatment

The Altim TD treatment for aluminium surface treatment

Keywords: Mofratech, Aluminium, Surface treatment

The Altim TD surface treatment process, patented by French company Mofratech, is believed to address huge application potential. It is developed from a micro-arc oxidation (MAO) process and is considered by its manufacturers to represent a full-scale technological revolution in aluminium surface treatment: it claims superior performance, with regard to hardness, substrate adherence, wear and corrosion resistance and electrical and thermal insulation. Mofratech informs us that, unlike thermal powder projection techniques, it can be used on the inside and the outside of parts; and unlike rival hard chrome processes, which are threatened by new environmental protection regulations, the Altrim TD process is non-polluting.

The numerous applications for Altim TD process include lubricated and non-lubricated friction parts (including high-speed parts), high-surface-hardness parts, and parts for pneumatic and hydraulic systems. Aluminium treated using this process will often prove to be a good replacement for other materials that carry weight or implementation penalties, such as steel, bronze and solid ceramic.

Altim TD treatment involves an electrolytic process that is said to differ from conventional anodisation in both power input and electrolyte. In an aqueous medium of slightly basic pH, micro-arcs are generated over the whole surface of the part by successive dielectric breakdowns in the hydroxide and oxide layers. The resulting electrochemical reactions in the microplasimas produce a hybrid ceramic that is mainly composed with alumina type a-A12O3- corundum, This ceramic layer is equally distributed inside and outside the metal surface and can have a useful thickness from 30 to 150pm, depending on the customer's requirements. The growth rate varies from 1 to 2mm per minute, depending on the alloy, the process and the application for the finished part.

According to Mofratech, the process offers unrivalled surface performance on many counts. Depending on the alloy, surface hardness can, it is claimed, reach 1,400 to 2,000HV. Adhesion is thought to be perfect since the ceramic coating is grown from the material itself, unlike being projected. The coating is also claimed to be highly resistant to corrosion (over 1,000 hours in salt spray test, after impregnation). Wear resistance is believed to be four times higher than hard anodized aluminium and three times higher than hardened 5,140 steel. Parts (even those of highly complex shapes) can be treated on the inside and outside. And because mating parts treated with the Altim TD process will have a very low coefficient of friction, the process is believed ideal for making lubricant-free guides. Impregnating with a permanent dry lubricant can further lower the coefficient of friction.

In addition, the coating can reportedly resist temperatures up to 2,000°C over very short periods of time, up to 1,250°C over three seconds, and up to 350°C under continuous duty. Electrical insulation is 500V for an 80mm thickness without impregnation and three times higher with suitable impregnation. The micro-porous coating has natural tribological properties and can take permanent impregnation of lubricants or can be used as a primer for lacquer, varnish or PTFE finishes.

As legislation moves in to curb the use of environmentally hazardous techniques, Altim TD is considered a highly attractive process that is said to be pollution-free, providing certain elementary precautions are taken.