M. Emamy
材料科学技术（英文）
Oxide films are incorporated into melts by an entrainment process, and are expected to be present in most
metals, but particularly cast Al alloys. The oxides are necessarily present as folded-over double films (bifilms)
that are effectively cracks. Their effect on the electrochemical behaviour of cast Al-5Zn-0.02In sacrificial
anodes was studied in 3 wt pct sodium chloride solution using the NACE e±ciency evaluation. Three methods
were employed to entrain progressive amounts of oxide in the alloy, including the addition of Al-Zn-In maching
chips to the charge, increasing the pouring height, and agitating the melt. The introduction of oxide bifilms
in the cast alloy resulted in the deterioration of the electrochemical properties of the sacrificial anodes, such
as current capacity and anode e±ciency, and introduced increasing variability in these properties. The results
suggest that corrosion behaviour is strongly related to the presence of bifilms suspended in the liquid alloy
because bifilms provide crack paths allowing the corrodant to penetrate deeply into the metal matrix, and
simultaneously provide localized galvanic cells because of the precipitation of Fe rich intermetallic compounds
on their outer surfaces.
关键词:
Aluminium
,
Sacrificial anode
,
Efficiency
,
Entrainment
,
Bifilm
