Blistering failure analysis of organic coatings on AZ91D Mg-alloy components

A batch of notebook personal computer components was manufactured from AZ91D Mg alloy by precision die-casting, subsequent chemical conversion and organic coatings. After storage for some time, some blisters were found on some components. SEM/EDS and FTIR analysis showed the blistering initiated because of in situ loss of adhesion at the organic coating/substrate interface, caused by contamination and/or corrosion. Data from accelerated environmental tests on deliberately contaminated model samples suggested that the blisters originated from contamination at the interface, and that the blistering was also related to the storage conditions. An empty blister forms at early time, and it gets filled with corrosion products later on, and corrosion further on, progress on these sports. An effective way to reduce blister formation is to avoid direct physical contact with all components in this product.