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Investigating the Effects of Heat Treatment and Ag Addition on the Microstructure, Mechanical Properties and Corrosion Behavior of

Saadatmand Hashemi, Shakiba | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56960 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Alizadeh, Reza; Ashuri, Hossein
  7. Abstract:
  8. Magnesium and its alloys are among the new degradable implants due to their characteristics such as biodegradability, low density, elastic modulus close to bone, and biocompatibility, which have received much attention from researchers. However, in most biological applications, the insufficient corrosion resistance of this alloy causes the accumulation of hydrogen gas around the implant, the loss of mechanical strength and its destruction before the completion of the treatment period. In this research, magnesium base alloys Mg–4Sn, Mg–4Sn–0.2Ag and Mg–4Sn–1Ag are investigated to improve mechanical strength and corrosion resistance. Finally, after casting and alloying, microstructural, mechanical and corrosion investigations were carried out on the samples in cast state and heat treatment. Observations of microstructures were done using optical and scanning electron microscopes, and the phase study was also done with X–ray diffraction analysis. The mechanical properties of molten metal alloys were evaluated by shear punch test. The results showed that adding 0.2% and 1% Ag to Mg–4Sn alloy increased the USS value from 89 to 103 and 104 MPa, respectively. By adding 0.2% of Ag to Mg–4Sn alloy, the corrosion potential decreases from –1.55 V to –1.65 V and the corrosion current density from 233.4 µA/cm to 4.258 µA/cm and with increasing the amount of Ag up to 1%, the potential decreases (–1.67 V) and the corrosion current density also decreased by 0.15 compared to the Mg–4Sn–0.2Ag alloy, and the value of Ri was the lowest in the Mg–4Sn and the highest for Mg–4Sn–0.2Ag alloy. Heat treatment made the microstructure homogenization and solubility of Mg2Sn deposits in the α–Mg field. Also, by performing heat treatment, the value of USS reached from 89 to 103 MPa for Mg–4Sn alloy, from 103 to 107 MPa for Mg–4Sn–0.2Ag alloy, and from 104 to 110 MPa for Mg–4Sn–1Ag alloy. Also, the value of Ecorr for the Mg–4Sn alloy after heat treatment compared to the as-cast condition decreased from –1.55 to –1.45 and the value of the current density from 4.33 µA/cm2 in the as-cast condition to 3.17 µA/cm2 after heat treatment increased. The value of Ecorr for Mg–4Sn–0.2Ag alloy did not change, and the value of Ecorr decreased from 4.258 µA/cm2 in the cast state to 4.25 µA/cm2 after heat treatment, and for the Mg–4Sn–1Ag alloy, the value of Ecorr increased to –0.76 V has been reached and the value of the current density has increased from 4.43 µA/cm2 in the pouring state to 4.6 µA/cm2 after heat treatment. The morphologic level of all samples was measured after 11–day immersion in the body simulating solution, which accelerated the improvement and the homogeneity of the progressive processes was observed in the heat treated samples
  9. Keywords:
  10. Heat Treatment ; Silver ; Mechanical Properties ; Corrosion Resistance ; Biodegradable Magnesium Alloys ; Magnesium-Tin Alloy ; Microstructure

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