Study on the Strengthening Mechanism of Rare Earth Ce in Magnesium Alloys, Based on First-Principle Calculations and Electronegativity Theory.

Yanfei Chen,Jixue Zhou,Zhengqiang Zhu,Huasheng Lai

doi:10.3390/ma14216681

Abstract

Since the commercial applications of rare earth magnesium alloys are increasing gradually, there are considerable advantages to developing lower cost and higher performance magnesium alloys with high abundance rare earth (RE) elements. However, the alloying order of a matrix magnesium alloy is completely changed with the addition of RE elements. Therefore, further study of the strengthening mechanism of Ce element in magnesium alloys is required. In this work, the thermodynamic stability of the possible second phases in a Mg-Al-Mn-Ce multicomponent magnesium alloy were analyzed, based on first-principle calculations, and the precipitation sequence of the key RE phases was deduced as a consequence. Combined with Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD), Energy Dispersive Spectrometer (EDS), and other experimental methods, it was investigated whether the preferentially precipitated second phases were the nucleation core of primary α-Mg. The complex alloying problem and strengthening mechanism in a multi-elemental magnesium alloy system were simplified with the aid of electronegativity theory. The results showed that the preferentially precipitated Al11Ce3 and Al10Ce2Mn7 phases could not be the nucleation core of primary α-Mg, and the grain refinement mechanism was such that the second phases at the grain boundary prevented the growth of magnesium grains. Moreover, the tensile test results showed that the reinforced structure, in which the Al-Ce phase was mixed with Mg-Al phase, was beneficial for improving the mechanical properties of magnesium alloys, at both ambient temperature and high temperature.

Highlights

Lightweight materials have become an important development direction for the transportation and aviation industries [1]
It was clear that the grains of the matrix magnesium alloy were equiaxed, with a size of about 600 μm
Rare earth magnesium alloys with Ce contents of 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, 0.8 wt.%, 1 wt.%, and 3 wt.% were prepared with this composition as a matrix in this work

Summary

Introduction

Lightweight materials have become an important development direction for the transportation and aviation industries [1]. As the lightest structural material, magnesium alloys have been increasingly used to replace some traditional materials in weight-critical applications, owing to their high specific strength/specific stiffness, recyclability, rich resources, and excellent process performance [2]. The poor heat resistance of magnesium alloy has limited its applications in certain fields [3]. According to the viewpoints in the literature [4,5], this was caused by the poor thermal stability of the strengthening phases in magnesium alloy (such as Mg17 Al12 , MgZn, Mg3 Sb2 , etc.), they might perform well at ambient temperature. As the slip system of magnesium alloy was only {0001}, at

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Conclusion