Novel aircraft Mg-Y-Gd-Ca alloys with high ignition temperature and suppressed flammability
Introduction
The replacement of aluminum parts with magnesium in the aviation industry would cause a reduction of weight of an airplane by up to 30% [1]. Such a reduction of weight would, therefore, results in a reduction of the burnt fuel and subsequently reduced CO2 emissions [2]. The great disadvantage of magnesium lies in the high affinity to oxygen which is problematic during the melting and casting as the magnesium oxide has no protective ability [3], [4], [5]. Moreover, the ignition of magnesium is dangerous especially in the aviation industry as it may lead to disastrous consequences due to its high flame temperature and problematic extinguishing. That was the main reason behind the recently lifted ban by the Federal Aviation Administration (FAA) of magnesium alloys in the aircraft cabin [6]. An ignition temperature of an alloy might be determined by the heating the sample in the furnace. The ignition temperature is thus identified by the sudden increase of temperature due to the burning of the sample [7].
It was investigated that some elements (Ca, Be, Gd, Y, Gd, Nd) significantly improves resistance to oxidation [5], [8], [9]. The properties of the layer depend on the amount of dissolved elements in the magnesium matrix as well as on the Pilling-Bedworth ratio (PBR) and the Gibbs free energy change for oxidation [8], [10]. Researchers agree that the ignition temperature is increased only if the amount of alloying element in the solid solution is above a certain limit as intermetallic phases have a lesser influence on the ignition properties.
This work proposes novel alloys with superior ignition-resistant properties with Y, Gd and Ca as alloying elements. The ignition temperature of alloys with different composition is determined and the oxide layer which prevented ignition is studied. It is illustrated that some of the novel alloys possess ignition temperature well above 1000 °C. Reasons for a high ignition resistance are studied by a detailed analysis of oxide layers of the alloys.
Section snippets
Sample preparation
Samples were prepared by melting the pure elements in the induction furnace at 750 °C for 0.5 h under a protective argon atmosphere (99.96%). The melt was cast into the cold brass mold with 50 mm in diameter. The final composition with the amount of alloying elements in the solid solution of each sample according to EDS is given in Table 1.
Microstructure characterization
Samples were firstly ground on the SiC papers P80-P4000, afterward they were polished on diamond pastes D2 and D0.7 (UR-diamant). The final polishing was
Microstructure characterisation
The microstructures of the as-casted ingots are shown in Fig. 1. One can see that all samples are composed of the dendritic microstructure. The dendrites consist of magnesium solid solution and interdendritic space enriched by alloying elements. The composition of the solid solution measured by EDS is shown in Tab 1. The amount of Y and Gd in the solid solution was increased with higher amount of alloying elements. However, the amount of Ca in the solid solution remained constant for all
Conclusion
The microstructures of as-casted ingots of alloys were characterized by general dendritic morphology. The concentration of Y and Gd in the solid solution of primary Mg increased with the overall amount of alloying elements in the alloy, while the amount Ca remained constant for all prepared materials. The ignition temperature of alloys was highly increased compared to the pure Mg and reached almost 900 °C for Mg-0.5Y-0.5Gd-0.3Ca alloy and even 1095 °C for Mg-2Y-2Gd-1Ca and Mg-4Y-4Gd-2Ca. Such a
CRediT authorship contribution statement
Drahomir Dvorsky: Writing - original draft, Writing - review & editing, Investigation, Formal analysis. Jiri Kubasek: Conceptualization, Validation, Resources. Dalibor Vojtech: Supervision, Project administration, Funding acquisition. Peter Minarik: Data curation, Formal analysis, Methodology.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The authors wish to thank the Czech Science Foundation (project no. GA19-08937S) and specific university research (MSMT No 21-SVV/2019) for the financial support of this research.
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