Evaluation of Corrosion Mechanisms of Hybrid Light Metal Structures by High Pressure Die Casting

In this study, aluminum sheet metal reinforced magnesium structures have been manufactured by high pressure die casting (HPDC). Selected interfaces of the hybrid structures were analyzed before and after exposure to corrosive environments. The characterization of the as cast bounding surfaces of aluminum sheets and magnesium cast alloys was carried out to quantify the appearance of crevices, which are significantly influencing the extent of the corrosive attack. Depending on the geometrical design of local bonding areas, the observed interface conditions varied from defect-free form closure to crevice widths beyond 35 μm. A minor percentage of the analyzed segments revealed areas of local metallic continuity, detected as intermetallic phases Al3Mg2 and Al12Mg17. In order to evaluate acting corrosion mechanisms, hybrid samples featuring the material combinations EN AW 5083 + AZ91 HP and EN AW 6082 + AM50 HP were subjected to immersion tests using 0.1M NaCl solution at a pH of 7.5. The results showed a strong influence by the spread of the potential difference. Alternating corrosion tests (VDA 621-415) were applied to prove effectiveness of cathodic dip coatings (CDP) and wax sealing on standard profile structures, since the uncoated Al-Mg samples sustained severe corrosion damages immediately.