Influence of ECAP process on mechanical and corrosion properties of pure Mg and ZK60 magnesium alloy for biodegradable stent applications

Abstract

Equal channel angular pressing (ECAP) was performed on ZK60 alloy and pure Mg in the temperature range 150–250 °C. A significant grain refinement was detected after ECAP, leading to an ultrafine grain size (UFG) and enhanced formability during extrusion process. Comparing to conventional coarse grained samples, fracture elongation of pure Mg and ZK60 alloy were significantly improved by 130% and 100%, respectively, while the tensile strength remained at high level. Extrusion was performed on ECAP processed billets to produce small tubes (with outer/inner diameter of 4/2.5 mm) as precursors for biodegradable stents. Studies on extruded tubes revealed that even after extrusion the microstructure and microhardness of the UFG ZK60 alloy were almost stable. Furthermore, pure Mg tubes showed an additional improvement in terms of grain refining and mechanical properties after extrusion. Electrochemical analyses and microstructural assessments after corrosion tests demonstrated two major influential factors in corrosion behavior of the investigated materials. The presence of Zn and Zr as alloying elements simultaneously increases the nobility by formation of a protective film and increase the local corrosion damage by amplifying the pitting development. ECAP treatment decreases the size of the second phase particles thus improving microstructure homogeneity, thereby decreasing the localized corrosion effects.

Grain size and texture dependence on mechanical properties, asymmetric behavior and low temperature superplasticity of ZK60 Mg alloy

“…Due to the low density, high specific strength and stiffness, excellent damping capacity and biocompatibility, magnesium and its alloys have been attracting much attention as potential metallic materials in a wide range of automotive, military, electronic, aerospace and biomedical applications [1][2][3][4][5][6]. However, Mg exhibits poor formability at room temperature due to its hexagonal closed-packed (HCP) crystal structure with limited number of available slip systems.…”

A Critical Review of Mg-Based Hydrogen Storage Materials Processed by Equal Channel Angular Pressing

“…ECAP could introduce an ultra-fine grained (UFG) structure with excellent mechanical properties, as well as unique physical and chemical performances. Intensive research had been carried out in the application of UFG alloy processed by ECAP, for example, in fabricating various micro-parts working in micro-electro-mechanical systems [8] and in making biodegradable stents in the biomedical field [9]. ECAP also can be used in improving the hydrogen storage property of Mg-based hydrogen storage materials.…”

Microstructural Evolution and Properties of a Hot Extruded and HPT‐Processed Resorbable Magnesium WE43 Alloy

“…[13][14][15][16][17] This approach can produce an ultra-fine crystal structure and even a nanocrystalline structure under optimum conditions, thereby leading to improved mechanical properties in terms of the Hall-Petch relationship. [18] Equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) are two of the most attractive SPD processing techniques where ECAP denotes the pressing of a bar through a die constrained within a channel that is bent through an abrupt angle and HPT denotes placing a disk in depressions between two massive anvils and then subjecting to a pressure, P, and concurrent torsional straining.…”