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.

Borate's effects on coatings by PEO on AZ91D alloy

“…Since PEO processes can form metallurgically bonded ceramic coatings on the non-ferrous metals, the PEO ceramic oxide coatings generally exhibit superior wear resistance, high thickness, high micro-hardness, and good adhesion to substrates. A large amount of studies on the mechanisms [8,11,12], process optimisation [13][14][15][16][17][18][19][20][21][22][23][24], properties and applications [25][26][27][28][29][30][31][32] of the PEO techniques have been conducted in the previous studies. Based on the previous results, it is believed that the thickness and density of the coatings play crucial roles in achieving better properties of wear resistance and corrosion resistance.…”

Protective compound coating on AZ91D Mg alloy fabricated by combination of cold spraying with die casting

“…There are many possible coating technologies available for Mg alloys. [8][9][10][11][12] However, due to the higher chemical activity of Mg in aqueous solutions, most of the existing surface treatment techniques failed to offer sufficient protection for Mg alloy components in their service environments.…”