Evolution of the microstructure and mechanical properties of WE43 magnesium alloy during multipass hot rolling

Abstract

The evolution of the microstructure and mechanical properties of WE43 magnesium alloy during multipass hot rolling was investigated. Results revealed that multipass hot rolling promoted the formation of small second phases, which was conducive to multiple dynamic recrystallization, consequently improving the microstructure homogeneity and refining the average grain size from 34.3 μm in the initial material to 8.83 μm. Meanwhile, the rolling deformation rotated abundant c-axis of the grains in the normal direction, resulting in a strong fiber texture. The yield strength in the rolling direction (RD) was improved from 164 MPa in the initial material to 324 MPa in the Pass 3 sheet due to fine-grained strengthening, second-phase strengthening, and texture modification. In addition, the distribution maps of the deformation mechanism indicated that the yield strength anisotropy between the RD and the transverse direction (TD) can be attributed to the effects of the texture component on the dominant mechanism. The dominant deformation mechanism during the tensile test was the prismatic slip caused by the strong basal texture of the RD, whereas it had a lesser proportion of prismatic slip under the influence of the weak basal texture of the TD. Compared to the basal slip, the higher critical resolved shear stress of the prismatic slip resulted in a higher increase in yield strength along the RD at approximately 51 MPa than that along the TD (RD: increase of 160 MPa; TD: increase of 109 MPa).

1. Introduction

Magnesium alloys have been widely used in the aerospace, automotive, electronics, and biomedical industries because of their low density, high specific strength, and excellent electromagnetic shielding performance [1–4]. However, their low absolute strength and poor formability seriously limit their widespread commercial usability [5–6]. In response to these limitations, rare-earth alloying can substantially improve the strength and formability of magnesium alloys based on solution strengthening [7–8] and precipitation strengthening [9].

Based on the principle of rare-earth alloying, WE43 magnesium alloys have excellent biocompatibility and are widely used in the field of biomedical applications [10]. With these magnesium alloys, Liu et al. [11] successfully prepared biodegradable scaffold microtubules with a 3.00-mm outer diameter and 180 μm thickness, which have been used in biomedical applications. However, the low strength and poor formability of WE43 alloys remain key factors that limit their widespread application [10].

Plastic processing technology is an effective way to further improve the strength and formability of WE43 magnesium alloys due to its positive role in grain refinement and texture modification. For example, Martynenko et al. [12] refined the grain size to 0.7–1.0 µm in WE43 alloys through equal channel angular processing, thereby producing noticeable fine-grained strengthening and subsequently contributing to excellent mechanical properties with a yield strength of 260 MPa and ductility of 13.2%. Similarly, Amani and Faraji [13] used cyclic expansion extrusion not only to refine the grain size but also to develop a bimodal texture component, thereby improving the yield stress and elongation to 330 MPa and 17%, respectively. By comparison, Liu et al. [14] employed single-pass rolling to obtain WE43 alloy sheets with a yield strength of 269 MPa and fracture elongation of only 0.9%. The mechanical properties of the rolled WE43 magnesium alloy are not up to that of the as-extruded. This phenomenon can be attributed to the poor plastic processing capability of WE43 magnesium alloy, which leads to its easy cracking and small deformation rolling. This characteristic severely influences the effect of plastic deformation on grain refinement, texture modification, and precipitation tailoring, weakening its role in strength and formability. Therefore, previous works demonstrated that multipass hot rolling can fully refine the grain size and modify the texture components in ZK60 magnesium alloy sheets, thereby improving the yield strength to 247 MPa and the fracture elongation to 17.6% [15]. However, for WE43 magnesium alloys, the effect of multipass hot rolling on microstructure and mechanical properties remains to be explored.