Abstract
Rare-earth-containing Mg alloys are a group of widely investigated alloys due to the disperse nano-sized precipitations formed during heat treatment. The underlying formation and strengthening mechanisms of precipitation is critical for their industrial applications. In this work, we systematically studied the evolution of precipitations in a Mg-10Gd alloy, based on the atomic-scaled TEM and HAADF-STEM observations. Especially, the in-depth transition mechanism from G.P. Zone to β”, β’, βT and βM is proposed, as well as their relationships with mechanical properties. It is found that blocking effect of precipitations improves the strength significantly, according to the Orowan mechanism. The elliptic cylinder shaped β’ phase, with a base-centered orthorhombic lattice structure, provides significant strengthening effects, which enhance the hardness and ultimate tensile strength from 72 HV and 170 MPa to 120 HV and 300 MPa.
Highlights
As the lightest structural metal in industrial applications, magnesium alloys have been intensively investigated due to their contributions in energy conservation and environment protection [1,2,3,4]
It is well established that the factor of Hall–Petch equation of Mg alloys is high, while the strengthening is difficult to achieve by work hardening, because of the low ductility [11,12,13,14,15,16,17]
Recent research has revealed that precipitation hardening is the most effective way to improve the strength of Mg alloys at both room temperature and elevated temperatures [18,19,20,21,22]
Summary
As the lightest structural metal in industrial applications, magnesium alloys have been intensively investigated due to their contributions in energy conservation and environment protection [1,2,3,4]. Owing to their hexagonal close-packed (HCP) lattice structure, the easy slip systems in Mg alloys are insufficient to support the stable plastic deformation at room temperature [5,6,7,8,9,10]. Aging treatment is an effective way to enhance the strength of Mg-Gd system alloys, owing to the disperse nano-sized precipitations. The structures of precipitations in Mg-Gd system alloys have a specific evolution sequence, which is proposed as: S.S.S.S
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