Microporosity formation in Mg alloys and its effect on protective coatings

Abstract

A notebook computer component with a complex geometry was manufactured with a die cast process (DCP), using an AZ91D alloy. Chemical conversion and organic coatings were sequentially applied to provide protection against physical and chemical damage. Air content in the component, which gives rise to microporosity, was determined with a DCP computer simulation using MAGMA software. The surface layer characteristics of the component were also investigated using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The microporosity content was higher at the end of the filling process compared with the regions that filled first. Corrosion resistance was poorer for discontinuous conversion coatings that resulted from surface microporosity. Moreover, adhesion of an organic coating was degraded at areas with higher microporosity.

Keywords:

• AZ91D
• Microporosity
• Simulation
• Coatings
• Corrosion
• Adhesion

Acknowledgements

The authors gratefully acknowledge the National Natural Science Foundation of China (grant nos. 51001079, 51044007 and 51374151), the Doctoral Found of Ministry of Education of China (grant no. 20091402110010), the China Postdoctoral Science Foundation (no. 20100471586) and the Natural Science Foundation of Shanxi Province (nos. 2011011020-2, 2010021023-1) for funding provided in support of this work.