Enhancement of the Mechanical Properties of an Mg–Zn–Ca Alloy Using High‐Pressure Torsion

Abstract

The structure and properties of an Mg-Zn-Ca alloy processed by high-pressure torsion (HPT) are investigated. Microstructure is studied by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. An enhanced microhardness of 990 MPa is observed in the HPTprocessed samples due to an uniform microstructure with a grain size of 150 nm. After additional annealing at 200 C, the ultrafine-grained alloy demonstrates an ultimate tensile strength of 270 MPa with a ductility of 9%.Mg and its alloys show great potential in biomedical applications due to its biocompatibility, low density, high strength-to-weight ratio, elastic modulus comparable to bone, and biodegradability. [1][2][3][4] It is known that magnesium alloys containing Al, Zn, Mn are toxic for human body. [5] Therefore, an alloy of the Mg-Zn-Ca system has been chosen for investigations, [6][7][8][9][10] because of low-toxicological effects on human body. The dissolution rate and tensile strength of Mg-based alloys having different contents of Zn and Ca have been considered in ref. [7,11,12] In particular, it has been observed that the content of Zn should not exceed 1%, [7,11] and the content of Ca is recommended to be within 0.3%. [12] On the basis of these observations, the Mg-1%Zn-0.13%Ca has been selected for investigations. It is known that the magnesium alloys of this system demonstrate rather weak mechanical properties. At the same time recent studies have shown that the application of severe plastic deformation results in the grain refinement of conventional magnesium-based alloys leading to significant enhancement of strength. [13][14][15][16][17][18] The aim of this work is to study the influence of grain refinement on the enhancement of mechanical properties of a Mg-Zn-Ca alloy processed by high-pressure torsion (HPT).

Evolution of microstructure and mechanical properties of an as-cast Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy processed by high pressure torsion

“…Increased width of stacking faults makes dislocation cross-slip and climb more difficult, which makes dynamic recovery slow and difficult, leading to an increased dislocation density and high strain hardening effect in the first several HPT turns. In previous work on SPD processing of Mg alloys, often a solution treatment was conducted before SPD [11,12,40], whereas in this study HPT was performed on the as-cast Mg-Gd-Y-Zn-Zr alloy containing LPSO and Mg3(Gd,Y) phases. The dislocations will pile up at these second phases in grain interiors and at grain boundaries, i.e.…”

“…For example, a uniform microstructure with a grain size of 150 nm and microhardness of 990 MPa were obtained in Mg-1Zn-0.13Ca (wt%) after HPT for 5 turns [11]. The ultrafine-grained structure in HPT-processed Mg-9.33Gd (wt%) is very stable, with grain sizes remaining about 100 nm during isochronal annealing up to 300 o C [12].…”

Microstructure and Hardness Evolution in Magnesium Processed by HPT

“…Many papers have reported the formation of ultrafine grained structures in pure magnesium [3][4][5][6] and AZ31 [7][8][9][10][11] , AZ61 12 , AZ80 13 , AZ91 [14][15][16] , ZK60 [17][18][19] , Mg-Zn-Y 20,21 , Mg-Gd-Y-Zr 22,23 , Mg-Zn-Ca [24][25][26][27] and Mg-Dy-Al-Zn-Zr 28 alloys. The processed alloys exhibit improved strength but also some papers report superplastic behaviour 16,19,22,29,30 , improved hydrogen storage properties 3,[31][32][33][34][35] and improved corrosion resistance 24,27,36 .…”

Effect of Solution Pretreatment on Homogeneity and Corrosion Resistance of Biomedical Mg–Zn–Ca Alloy Processed by High Pressure Torsion

“…As a result, ultra‐fine grain material can be prepared . Grain refinement has significant effect on the improvement of mechanical properties . In ref., after HPT at N = 0.5 revolution, ultimate tensile strength of pure magnesium was obviously improved compared with as‐received.…”