Controlled Grain Refinement of Biodegradable Zn-Mg Alloy: The Effect of Magnesium Alloying and Multi-Pass Hydrostatic Extrusion Preceded by Hot Extrusion

Abstract

To satisfy the most stringent criteria in terms of new cardiovascular stents, pure Zn was alloyed with 1 wt pct of Mg and subsequently subjected to plastic deformation, using conventional hot extrusion followed by multi-pass hydrostatic extrusion. A detailed microstructural and textural characterization of the obtained materials was conducted, and mechanical properties were assessed at each pass of deformation process. In contrast to pure Zn, hydrostatically extruded low-alloyed Zn is characterized by a remarkable increase in strength and ductility (YS = 383 MPa, E = 23 pct), exceeding the values needed for stents. Such behavior is associated with a dual microstructure containing fine-grained Zn, alternatively arranged with bands of a fragmented eutectic. Extensive grain refinement was achieved due to the process of continuous dynamic recrystallization. Hydrostatic extrusion changes the initial $$ \langle 10\bar{1}0\rangle $$ ⟨ 10 1 ¯ 0 ⟩ fiber texture to a 〈0002〉 and $$ \langle 10\bar{1}1\rangle $$ ⟨ 10 1 ¯ 1 ⟩ double fiber texture in which the 〈0002〉 component decreases with each pass of hydrostatic extrusion. The gradual evolution of texture components was simulated using a visco-plastic self-consistent model, which confirmed that, during hydrostatic extrusion, secondary slip systems were activated involving mostly the pyramidal one.

Fine-tuning of mechanical properties in a Zn–Ag–Mg alloy via cold plastic deformation process and post-deformation annealing

“…As reported, Zn alloys containing Mg additions exhibit satisfactory mechanical strength due to the presence of a highly strengthening Mg-rich eutectic phase [ 18 , 19 ]. However, the highly-soluble Ag addition can provide both solid-solution strengthening and improvement of mechanical properties by tuning the fraction of Ag-rich phases [ 5 , 20 ].…”

Dynamic Recrystallization and Its Effect on Superior Plasticity of Cold-Rolled Bioabsorbable Zinc-Copper Alloys

“…In the case of Zn-1Cu, the effect of CDRX in forming refined, equiaxed micro-structure was limited due to the static recrystallization process, which caused grain growth and heterogeneous microstructure. The contribution of CDRX to grain refinement of Zn-based materials was also observed for other methods of plastic deformation such as Equal Channel Angular Pressing (ECAP) or hydrostatic extrusion [9,[23][24][25][26][27].…”

Texture-Based Optimization of Crystal Plasticity Parameters: Application to Zinc and Its Alloy

“…This can lead to their activation provided that also the critical value of the resolved shear stress (RSS) at a given temperature for those systems is sufficiently low. In the case of pure Zn, the compressive twinning presents significant and prismatic slip systems and crystallographic orientation [10] for different passes for pure Zn. Note that the scale changes for different passes.…”

“…Analysis was performed only for points indexed as a-Zn phase. Second phase of Mg2Zn11 particles [10] is marked by black color on EBSD maps. It was assumed that at least 5 measurement points surrounded by continuous grain boundary with misorientation angle 15 degree is required to fulfill the grain definition.…”

“…It was recently reported that improvement in both strength and plasticity of pure zinc can be achieved by alloying with magnesium and by subjecting material to hydrostatic extrusion. [10][11][12] Those papers focus mainly on experimental studies relating microstructure with mechanical properties of pure zinc and low-alloyed zinc with addition of 1 wt pct of Mg.…”