Characterization of different corrosion protection systems on magnesium alloys for applications in the automotive industry

摘要

In order to characterize different corrosion protection systems on magnesium alloys for applications in the automotive industry, several commercially available pre-treatments (conversion coating and plasma electrolytic oxidation) were analyzed by means of electrochemical techniques as well as hydrogen evolution measurements. The characterized commercial conversion coatings included Bonderite® M-NT 160/161 (Henkel AG & Co. KGaA), Decorrdal® Al 240 A (Kluthe GmbH), Gardobond® X4729 (Chemetall GmbH), MagPass® (AHC Oberflachentechnik GmbH), Oxsilan® 9802 (Chemetall GmbH) and ST650® (SurTec GmbH). The analyzed plasmaelectrolytic oxidation coatings included Ceranod® (Eloxalwerke Ludwigsburg GmbH), Keronite® (Keronite Ltd.), Bonderite® MGC (Henkel AG & Co. KGaA) and MagOxid® (AHC Oberflachentechnik GmbH). In addition to the characterization of the corrosion protection primers, salt spray testing (INKA-test) was performed on samples exhibiting a three-layered painting structure including electrocoating and powder coating. The three-layered painting systems were characterized in terms of corrosion at the free corrosion potential and under conditions of galvanic corrosion. The latter included the assembly of Mg-alloys with a three-layered coating structure and electrocoated Al-alloy by means of self-piercing rivets, flow drilling screws and blind rivets. The correlation of electrochemistry and the INKA-test was proven by an identical ranking of the analyzed coatings.