Performance of new pretreatment technologies as substitute for zinc phosphating in the automotive multi-metal-process for corrosion protection

New thin layer pretreatment technologies on various steel and aluminium substrates are compared with the standard zinc phosphate pretreatment. Their corrosion protection properties in combination with EDP in the multi-metal-substrate-process are investigated. One important aspect of this study is the correlation of the anti-corrosion behaviour at intensified outdoor weathering with the cyclic corrosion test according to VDEh standard SEP 1850, respectively VDA standard 233-102. Both tests are performed as round-robin. Studies of water and electrolyte migration into the interfaces give a better insight into corrosion mechanisms on pretreated multi-metal substrates. The interfaces of interest are between metal and conversion layer and/or conversion layer and organic coating. Electrochemical, kinetic and energetic studies with methods as EIS, SKP and surface energy measurements besides surface and interfacial measurements with FIB/SEM will help to understand the mechanisms. First results from cyclic corrosion tests and scientific evaluation of material properties are presented. An outlook will be given concerning the benefit of the completed study for manufacturers of steel, organic coatings and pretreatment chemistry for the automotive industry.