The Influence of Ca and Y on the Microstructure and Corrosion Resistance of Vacuum Die Casting AZ91 Alloy

TL;DR

This study examines how adding calcium and yttrium to AZ91 magnesium alloy affects its microstructure and significantly improves its corrosion resistance, as demonstrated through various microscopic and electrochemical tests.

Contribution

It reveals that Ca and Y refine microstructure, reduce Mg17Al12 phases, and form new phases, greatly enhancing corrosion resistance of AZ91 alloy.

Findings

Microstructure is refined with Ca and Y addition.

Corrosion rate decreases to 16.2% of original with Ca and Y.

Corrosion current density drops by an order of magnitude.

Abstract

The influence of Ca and Y on the microstructure and corrosion resistance of vacuum die casting AZ91 alloy is investigated using optical microscope, electron scanning microscope, weight-loss test and electrochemical corrosion test. The results indicate that the microstructure of AZ91 alloy can be refined, amount of Mg17Al12 phases is reduced, making Mg17Al12 phases transform from banding to reticular, and stringer Al2Ca phases and block Al2Y phases are formed through adding both Ca and Y. The corrosion resistance of AZ91 magnesium alloy can be increased greatly by adding both Ca and Y. The corrosion rate of AZ91-1.5Ca-1.0Y alloy is dropped to 16.2% of that of AZ91 alloy immersed in 3.5% NaCl aqueous solution for 24 hours. The corrosion current density of AZ91-1.5Ca-1.0Y alloy is dropped by one order of magnitude.