Additive Manufacturing result is a thin oxide layer on the surface that protects the part from corrosion . “ Anodization is typically applied to aluminium components and uses acidic electrolytes to form a corrosion resistant , hardened surface layer ,” continues Laghaei . “ Unfortunately , these electrolytes are not environmentally friendly and struggle to properly coat sharp edges and corners , which is required for the delicate fins within a heat exchanger .” Anodization is unsuitable for a range of aluminium alloys , including the high-silicon alloys commonly used in AM , and can also suffer defects such as cracking on certain geometries such as sharp edges . PEO does not have these drawbacks as it can coat significantly more alloy types with robust , highly dense surfaces , regardless of geometric features .
Plasma Electrolytic Nitriding ( PEN ) To help solve the lack of corrosion protection for aluminium parts , Conflux is collaborating with Deakin University to develop a new type of PEO process , called Plasma Electrolytic Nitriding ( PEN ). PEN , also known as plasma nitriding , is a surface modification technique used on various metals , including steel , to enhance surface hardness and wear resistance . It involves introducing nitrogen ions into the metal surface using plasma in a nitrogen-containing environment ( i . e ., electrolyte ). “ Our initial research shows that we can coat parts within a couple of minutes , compared to 30 minutes with traditional anodization techniques . This faster process drastically reduces the amount of energy and chemicals needed ,
resulting in 3D printed parts with higher performance , at much cheaper costs ,” continues Fordyce . “ We have advanced the PEO process further by developing new coating electrolytes which contain nitrogen , the basis for our Plasma Electrolytic Nitriding ( PEN ) technology . PEN has proven to provide even greater corrosion protection than PEO . We started developing this for aluminium heat exchangers , but we are now realising that it can be used on any aluminium alloys and so has the potential to be used in a wide variety of applications .” The other benefit to this innovative process is that parameters such as the time , current and voltage can be varied to tune the thickness of the coating . This ensures that for complex geometries such as micro channels and fins created through additive manufacturing , the coating is made thin enough ( 2 to 5 µ m thick , depending on parameters ) to avoid impeding fluid flow . The process can also be controlled to coat specific areas of a component , leaving other areas uncoated .
Conclusion Today ’ s additive manufacturing technology is allowing more complex geometries to be printed than ever before . Yet , only when the most suitable powders are selected for the right application can these parts truly achieve high performance . Innovative processes such as the PEN Conflux are developing with Deakin University have the potential to further enhance heat exchanger performance . This together with optimising printing parameters can make 3D printed heat exchangers suitable for all types of applications , from rockets to racecars .