Effect of Ca addition on the oxidation resistance of AZ91 magnesium alloys at elevated temperatures

Abstract

AZ91 magnesium alloys containing 0.27-5.22 wt.% Ca, were melted and cast to study the effects of Ca addition on oxidation resistance at elevated temperatures. An ignition temperature test showed that the ignition of AZ91 alloy occurred at about 350-450°C below the melting point, whereas that of the Ca-containing AZ91 alloys did so at above 650°C. Weight gain measurements indicated that the oxidation resistance of the AZ91 alloys improved with Ca addition. The oxidation rate was dependent on the oxidation temperature. In the temperature range of 300-400°C, the oxidation rate increased linearly. By contrast, the weight of 5 wt.% Ca-containing AZ91 alloy increased slowly due to the formation of a protective oxide layer. The oxidized surfaces were analyzed with low-angle XRD, FE-SEM equipped with EDS and AES. Complex structures were found in the oxide layers of the Ca-containing alloys: the outer layer mainly consisted of CaO, which was of uniform thickness, and the inner layer was a mixture of CaO, MgO, and Al 2 O 3 . In contrast to the loose and porous MgO formed on the surface of AZ91, the compact and dense oxide layers acted as an effective barrier to the further oxidation of the Ca-containing AZ91 alloys.

Effect of Ca and CaO on the High Temperature Oxidation of AZ91D Mg Alloys

“…4,5) In these studies, the inner layer was either a mixture of (MgO, CaO) in the case of Mg + (0:5$3) mass% Ca alloys, 4) or a mixture of (MgO, CaO, Al 2 O 3 ) in the case of AZ91 + (0:3$5) mass% Ca alloys. 5) AZ91D is the Al-rich, high-strength cast Mg alloy that is most widely used.…”

Closed Die Forging of Mg-Al-Zn-Ca-Y Alloys

“…While the understanding of these Ca containing alloys, in terms of oxidation and casting behaviour, has vastly increased in the recent years [18,19,20], their forming capabilities on the other hand have not yet been in the focus of intense investigations. Those investigations are necessary if this promising alloy system is to be employed in industrial applications.…”

Microstructure and mechanical properties of rheo-squeeze casting AZ91-Ca magnesium alloy prepared by gas bubbling process

“…Fan et al [3] studied the combined addition of Y and Ce into pure Mg and found that some Mg-Y-Ce alloys could melt safely at 1173 K in air without any protection. Choi et al [4] investigated the effect of Ca addition on oxidation resistance of AZ91 Mg alloy at elevated temperatures and proved that the oxidation rate of Ca-containing AZ91Mg alloys decreased significantly. Among these ignition-proof alloying elements, Ca is thought to be more suitable than others, on account of its low density, extensive source and nontoxicity.…”