Electron microscopic studies of anodic oxide films on the AZ91HP alloy

Abstract

A Mg-9wt.Al-1wt.%Zn-alloy was anodized up to 90 V with constant current/constant voltage in an electrolyte which contained the compounds of the HAE-process (KOH, Al(OH) 3 , KF, Na 3 PO 4 and KMnO 4). Electron microscopic examinations revealed a highly porous and irregular film structure. The distribution of the elements in the film was measured with energy dispersive spectrometry on specimens prepared in cross section for the transmission electron microscope. The main characteristic found was a fluoride-enriched zone of about 100 nm thickness at the metal / film interface. Practically no manganese from the permanganate was detected in this fluoride-enriched zone.