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Investigating the Effects of Heat Treatment and Y Addition on the Microstructure, Mechanical Properties and Corrosion Behavior of Bio-Degradable Mg–Si Alloys

Jamalpour, Mohammad | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56155 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Alizadeh, Reza
  7. Abstract:
  8. In Mg–Si alloys, both primary and eutectic Mg2Si particles normally appear with sharp edges, which can lead to weak mechanical properties as the result of stress concentration at the sharp corners of these brittle particles. On the other hand, the morphology, size and distribution of Mg2Si particles affect corrosion behavior of Mg–Si alloys. Thus, it would be of great importance to modify the morphology of these particles. In this study, microstructure modification mechanisms after 0.5 wt% Y addition and heat treatment (HT) at 420 ◦C for 24 h are comprehensively studied in hypo-eutectic Mg–1Si and hyper-eutectic Mg–2Si alloys. Microstructural observations were performed using optical and scanning electron microscopy equipped with electron disperse spectroscopy, while phase analysis was done by X-ray diffraction. Mechanical properties of the studied alloys were evaluated by shear punch testing technique. The obtained results indicate that 0.5% Y addition to the as-cast Mg–1Si and Mg–2Si alloys could modify morphology of the eutectic Mg2Si from coarse lamellar to very short rod-shaped. The poisoning effect of Y was the main mechanism for this modification. The ultimate shear strength (USS) increased after Y addition to the Mg–1Si and Mg–2Si alloys, due to the modified eutectic Mg2Si morphology and also formation of fine Y-containing particles. So that after adding Y to the Mg–1Si alloy, the value of USS increased from 81 to 116 MPa (43% increase). By adding Y to the Mg–2Si alloy, the USS value increased from 88 to 132 MPa (50% increase). Also, the addition of Y to the as-cast Mg–1Si alloy increased the corrosion resistance. So that after adding Y to the as-cast Mg–1Si alloy, the corrosion current decreased from 5.60 to 3.24 μA/cm2. On the contrary, the addition of Y to the as-cast Mg–2Si alloy decreased the corrosion resistance. So that after adding Y to the as-cast Mg–2Si alloy, the corrosion current increased from 3.91 to 4.98 μA/cm2. In addition, it was observed that HT could change the morphology of the eutectic Mg2Si phase to short rod-shaped or point-shaped in the studied alloys. The USS values for the Mg–1Si and Mg–2Si alloys increased after HT, due to the modified morphology of Mg2Si particles. So, after applying HT on the as-cast Mg–1Si alloy, the value of USS increased from 81 to 100 MPa (23% increase). In addition, after applying HT on the Mg–2Si alloy, the USS value increased from 88 to 100 MPa (12% increase). Also, after applying HT on the as-cast Mg–1Si and Mg–2Si alloys, the corrosion resistance improved due to the modification of the eutectic Mg2Si particles. So that after applying HT on the as-cast Mg–1Si alloy, the value of corrosion current decreased from 5.60 to 4.31 μA/cm2. Also, after applying HT on the as-cast Mg–2Si alloy, the value of the corrosion current decreased from 3.91 to 2.07 μA/cm2 after HT
  9. Keywords:
  10. Silicon Bearing Magnesium Alloys ; Heat Treatment ; Yttrium ; Mechanical Properties ; Cast Alloy ; Biodegradable Magnesium Alloys ; Corrosion Resistance ; Ultimate Strength

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