Characteristics of Mg-Based Sintered Alloy with Au Addition

Abstract

The magnesium-based alloys produced by mechanical alloying (MA) are characterized by specific porosity, fine-grained structure, and isotropic properties. In addition, alloys containing magnesium, zinc, calcium, and the noble element gold are biocompatible, so they can be used for biomedical implants. The paper assesses selected mechanical properties and the structure of the Mg₆₃Zn₃₀Ca₄Au₃ as a potential biodegradable biomaterial. The alloy was produced by mechanical synthesis with a milling time of 13 h, and sintered via spark-plasma sintering (SPS) carried out at a temperature of 350 °C and a compaction pressure of 50 MPa, with a holding time of 4 min and a heating rate of 50 °C∙min^-1 to 300 °C and 25 °C∙min^-1 from 300 to 350 °C. The article presents the results of the X-ray diffraction (XRD) method, density, scanning electron microscopy (SEM), particle size distributions, and Vickers microhardness and electrochemical properties via electrochemical impedance spectroscopy (EIS) and potentiodynamic immersion testing. The obtained results reveal the compressive strength of 216 MPa and Young's modulus of 2530 MPa. The structure comprises MgZn₂ and Mg₃Au phases formed during the mechanical synthesis, and Mg₇Zn₃ that has been formed during the sintering process. Although MgZn₂ and Mg₇Zn₃ improve the corrosion resistance of the Mg-based alloys, it has been revealed that the double layer formed because of contact with the Ringer's solution is not an effective barrier; hence, more data and optimization are necessary.

Keywords: magnesium alloys; mechanical alloying; spark plasma sintering.

Figure 1

X-ray diffraction pattern of the Mg–Zn–Ca–Au alloy sample after 13 h milling.

Figure 2

X-ray diffraction pattern of the Mg–Zn–Ca–Au sintered alloy.

Figure 3

The SEM images of the Mg₆₃Zn₃₀Ca₄Au₃ powder after 13 h milling. Both images represent powder samples with different magnifications: (a) 500× and (b) 150×, the number in the images refer to the analysis results presented in Table 2.

Figure 4

The SEM image with featured regions of the EDS analysis (marked with the Arabic numerals, the EDS values shown in the Table 2) obtained for the sintered Mg₆₃Zn₃₀Ca₄Au₃ alloy. Area marked with “I” and “II” refers to the (a) and (b) images, respectively, where the intercrystalline fractures can be seen. The region marked as “III” is presented in Figure 5.

Figure 5

The SEM image with the region marked as “III” in the Figure 4 obtained for the sintered Mg₆₃Zn₃₀Ca₄Au₃ alloy. The image features the transcrystalline fracture.

Figure 6

EDS chemical composition map for the powder sample of the Mg₆₃Zn₃₀Ca₄Au₃ alloy.

Figure 7

EDS chemical composition map for the sintered sample of the Mg₆₃Zn₃₀Ca₄Au₃ alloy.

Figure 8

The SEM image featuring MgZn₂ phase regions in the powder sample. The numbers in the image refer to the EDS analysis results which are showcased in Table 4.

Figure 9

The SEM image featuring MgZn₂ phase regions in the sintered sample. The numbers in the image refer to the EDS analysis results which are showcased in Table 5.

Figure 10

Granulometry chart of the Mg–Zn–Ca–Au powder alloy after 13 h of milling.

Figure 11

The microhardness results for (a) Mg–Zn–Ca–Au powder alloy after 13 h of milling and (b) Mg–Zn–Ca–Au sintered alloy.

Figure 12

Polarization curve for the Mg–Zn–Ca–Au sintered alloy.

Figure 13

Impedance spectra obtained for Mg–Zn–Ca–Au sintered alloy. (a) Nyquist diagram, (b) Bode’s diagram. The symbols in (b) refer to the amplitude (circles) and phase spectra (“plus” sign).

Figure 14

Electrical equivalent circuit of the corrosion system for samples made of Mg–Zn–Ca–Au sintered alloy.