Excellent age hardenability with the controllable microstructure of AXW100 magnesium sheet alloy

Sumi Jo,Sangbong Yi,Lawrence Whitmore,Ainhoa Urrutia Aramburu,Sangkyu Woo,Dietmar Letzig

doi:10.1038/s41598-020-79390-z

Sumi Jo, Sangbong Yi + Show 4 more

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https://doi.org/10.1038/s41598-020-79390-z

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Abstract

Age-hardenability and corresponding improvement of the mechanical properties of Mg–1Al–0.7Ca and Mg–1Al–0.7Ca–0.7Y alloy sheets are addressed with respect to the microstructure and texture evolution during thermomechanical treatments. A fine grain structure and weak texture with the basal pole split into the sheet transverse direction are retained in the Mg–1Al–0.7Ca–0.7Y sheet even after the homogenization at 500 °C, due to the grain boundary pinning by Y-containing precipitates possessing a high thermal stability. Contrarily, the Mg–1Al–0.7Ca sheet shows a coarse microstructure and basal-type texture after the homogenization. The peak-aged condition is attained after the aging at 250 °C for 1800 s of both homogenized sheets, while the Y-containing sheet shows a higher hardness than the Mg–1Al–0.7Ca sheet. TEM analysis and thermodynamic calculation show the formation of metastable precipitates composed of Al, Ca, Y and Mg in the Mg–1Al–0.7Ca–0.7Y sheet at the homogenized and peak-aged conditions. A significant increase in the yield strength is obtained in the peak-aged condition from 162 MPa after the homogenization to 244 MPa, which arises from the increased size and number density of the precipitates. The high age-hardenability of the Mg–1Al–0.7Ca–0.7Y sheet attributes to the superior mechanical properties with an improved ductility promoted by the weak texture.

Highlights

Age-hardenability and corresponding improvement of the mechanical properties of Mg–1Al–0.7Ca and Mg–1Al–0.7Ca–0.7Y alloy sheets are addressed with respect to the microstructure and texture evolution during thermomechanical treatments
The secondary phases aligned along the rolling direction (RD) are M g2Ca phase in AX10, and Mg2Ca and Mg2Y phases in AXW100, which were not dissolved during the homogenization treatment of the cast materials
The thermal stability of these phases are shown from the thermodynamic calculation, which indicates the corresponding phases are formed as primary phase at the equilibrium conditions (Fig. 7)

Summary

Introduction

Age-hardenability and corresponding improvement of the mechanical properties of Mg–1Al–0.7Ca and Mg–1Al–0.7Ca–0.7Y alloy sheets are addressed with respect to the microstructure and texture evolution during thermomechanical treatments. Y is well acknowledged as an effective element for improving formability of Mg alloys by texture weakening in correlation with the change in stacking fault e nergy[29], and for improved strength via age-hardening[30,31]. In this regard, the role of Ca and Y on the age hardenability and texture evolution is examined by performing a comparative study of AX10 sheet from its Y-containing counterpart AXW100 alloy. The microstructural features of the both alloys were investigated by using a transmission electron microscopy (TEM) including high-resolution TEM and energy-dispersive X-ray spectroscopy (EDS), and thermodynamic calculation

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