Aluminium surface treatment
Aluminium surface treatment
Keywords: Mofratech, Surface treatment
The Altim TD® surface treatment process patented by French company Mofratech is thought to address huge application potential. It is developed from a micro-arc oxidation (MAO) process and is claimed 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. According to Altim, 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 Altim TD process is said to be non-polluting.
The numerous applications for Altim TD process are said to include lubricated and non-lubricated friction parts (including high-speed parts),high-surface-hardness parts, and parts for pneumatic and hydraulic systems. In Altim's opinion 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. The breadth of application is thought to be enormous, covering areas as diverse as shipbuilding, weaponry,automotive engineering, aerospace, electronics, electrical engineering, textile machinery and household appliances.
Altim TD treatment involves an electrolytic process that differs 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 microplasmas produce a hybrid ceramic that is mainly composed of alumina type alpha -Al2O3-corundum. This ceramic layer is equally distributed inside and outside the metal surface and can reportedly have a useful thickness from 30-150µm, depending on the customer's requirements. The growth rate varies from 1-2µm per minute,depending on the alloy, the process and the application for the finished part.
The Altim TD process is believed to offer unrivalled surface performance on many counts. Depending on the alloy, surface hardness can reportedly reach 1,400-2,000HV. Adhesion is stated to be perfect since the ceramic coating is grown from the material itself, unlike being projected. The coating is reported to be highly resistant to corrosion (over 1,000 hours in salt spray test, after impregnation). Wear resistance is said to be four times higher than hard anodized aluminium and three times higher than hardened 5140 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 thought to be ideal for making lubricant-free guides. Impregnating with a permanent dry lubricant can further lower the coefficient of friction.
In addition, the coating can 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 80µm 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 believed to be a highly attractive process that is said to be pollution-free, provided that certain elementary precautions are taken.
Further details are available from FTPB. Tel: +44 (0)20 7235 5330; Fax: +44(0)20 7235 2773; e-mail: rob-williams.ftpb@cfme.com
