Influence of Y and Nd on deformation mechanisms and tensile properties at room temperature of Mg-Zn-Gd alloy

Abstract

The microstructure, fracture mechanisms, deformation modes, and their correlation with the mechanical properties of Mg-Zn-Gd alloys were analyzed, considering the influence of Y and Nd additions. Increasing Y content and decreasing Nd content resulted in an increase in grain size from 17.2 to 29.2 μm, and two types of LPSO phases, 14H and 18R, formed in the alloy. The mechanical properties of the alloys were predominantly influenced by the LPSO phase, with the grain size effect being relatively minor. Based on this analysis, higher Y and lower Nd contents enhanced the tensile strength, yield strength, and elongation of the alloys, with additional improvements observed following solid solution treatment. Changes in Y and Nd content caused a shift in fracture patterns, transitioning from ductile fracture to brittle fracture and then to mixed fracture. Following solid solution treatment, the alloy progressively transitions from intergranular to a combination of ductile and deconvolutional fracture. The deformation modes observed at each stage are as follows: an increase in LPSO phases and twins activates pyramidal slip and suppresses prismatic slip.

1. Introduction

Magnesium, as a lightweight material, has applications in various engineering fields. Comprising 2.7 wt% of the Earth’s crust, it is the eighth most abundant element available [1]. However, the limited strength and plasticity of Mg alloys restrict their broader utilization [2−4]. Thus, improving the mechanical properties of Mg alloys remains a critical challenge for expanding their applications. To achieve high strength and satisfactory ductility, significant research efforts have been directed toward developing high-performance Mg alloys, with several high-strength variants being reported [5, 6]. Typically, the mechanical properties of Mg alloys are enhanced through a combination of alloying, heat treatment, grain refinement, and similar methodologies [2, 7−9]. Among these strategies, the strategic use of alloying elements plays a crucial role. Rare earth (RE) elements have proven to be highly effective in enhancing the properties of Mg alloys and are widely utilized in both steel and non-ferrous alloys [10]. In the context of high-strength Mg alloys, the beneficial impact of RE elements has been increasingly recognized and harnessed [11−16].

ZHANG et al [17] examined the impact of cooling rates on the tensile properties and fracture mechanisms of as-cast Mg-Nd-Zn-Zr alloys, providing insights into how cooling influences mechanical performance. CHEN et al [18] investigated the role of stacking faults in the tensile properties of Mg-4.05Y-2.47Nd-1.17Gd-0.52Zr alloys subjected to ultrasonic surface rolling processing, highlighting the influence of microstructural features on mechanical behavior. HARJO et al [19] explored the effects of low-ratio hot extrusion on Mg-Zn-Y alloys, emphasizing the roles of α-Mg and long-period stacking ordered (LPSO) phases in mechanical strengthening. WANG et al [20] studied Nd content in Mg-7Gd-0.5Zr alloys, discovering that Nd reacts with Mg to form Mg41Nd5 particles which enhance grain refinement through heterogeneous nucleation and improve thermal stability. ZHONG et al [21] investigated combined additions of Y and Ce in as-rolled Mg-8Li-1Al alloys (LA81), finding improvements in mechanical properties and isotropy. XIE et al [22] analyzed isothermal aging effects at ...