• Journal of Korea Foundry Society
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• v.41 no.6
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• pp.535-542
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• 2021

In this study, to improve the interfacial bond strength of cast iron-aluminum dissimilar materials, graphite was removed to a certain depth from the cast iron surface through de-graphitization heat treatment. As the heat treatment time increased, the depth at which graphite was removed increased, showing a linear relationship between the heat treatment time and depth. Aluminum was filled to a certain depth on the de-graphitized cast iron surface through die-casting method, and no intermetallic compounds were formed on the cast iron-aluminum interface. The interfacial bonding strength showed a value of 90 MPa regardless of the heat treatment time, which is very high compared to the 12MPa bonding strength of the material without de-graphitization heat treatment. This result is thought to be due to the mechanical bonding of the undercut structure as the liquid aluminum, penetrated by the high pressure die-casting process, solidified in the de-graphitized region of the cast iron.

• Korean Journal of Materials Research
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• v.33 no.10
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• pp.393-399
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• 2023

In this study, changes in the microstructure and mechanical properties of cast and extruded Al-2Li-1Ce alloy materials were investigated as the Mg content was varied. The density decreased to 2.485, 2.46 and 2.435 g/cm³ when the Mg content in the Al-2Li-1Ce alloy was increased to 2, 4 and 6 wt%, respectively. Intermetallic compounds of Al₁₁Ce₃ were observed in all alloys, while the β-phase of Al₃Mg₂ was observed in alloys containing 6 wt% of Mg. In the extruded material, with increasing Mg content the average grain size decreased to 84.8, 71.6 and 36.2 ㎛, and the fraction of high-angle grain boundaries (greater than 15°) increased to 82.8 %, 88.6 %, and 91.8 %, respectively. This occurred because the increased Mg content promotes dynamic recrystallization during hot extrusion. Tensile test results showed that as the Mg content increased, both the yield strength and tensile strength increased. The yield strength reached 86.1, 107.3, and 186.4 MPa, and the tensile strength reached 215.2, 285, and 360.5 MPa, respectively. However, it is worth noting that the ductility decreased to 27.78 %, 25.65 %, and 20.72 % as the Mg content increased. This reduction in ductility is attributed to the strengthening effect resulting from the increased amount of dissolved Mg, and grain refinement due to dynamic recrystallization.

• Archives of Metallurgy and Materials
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• v.65 no.4
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• pp.1317-1322
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• 2020

The present study investigated various thermodynamic parameters, microstructures and electrochemical behaviors of TiMoVCrZr and Ti-rich TiMoVCrZr high-entropy alloys (HEAs) prepared by vacuum arc remelting. The microstructures of the alloys were analyzed using X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM), and potentiodynamic polarization tests. The determined thermodynamic values of the Ω-parameter and the atomic size difference (δ) for the HEAs were determined to be in the range of Ω ≥ 1.1, and δ ≤ 6.6% with valance electron configuration (VEC) ≤ 5.0, suggesting the HEAs were effective at forming solid solutions. XRD patterns of the equiatomic Ti₂₀Mo₂₀V₂₀Cr₂₀Zr₂₀ HEA revealed four phases consisting of the body centered cubic1 (BCC₁), BCC₂, hexagonal close-packed (HCP), and intermetallic compound Cr₂Zr phases. Three phases were observed in the XRD patterns of Ti-rich Ti₄₀Mo₁₅V₁₅Cr₁₅Zr₁₅ (BCC, HCP, and Cr₂Zr) and a single BCC phase was observed in Ti-rich Ti₆₀Mo₁₀V₁₀Cr₁₀Zr₁₀ HEAs. The backscattered-electron (BSE) images on the equiatomic Ti₂₀Mo₂₀V₂₀Cr₂₀Zr₂₀ HEA revealed BCC and HCP phases with Cr₂Zr precipitates, suggesting precipitation from the HCP solid solution during the cooling. The micro-segregation of Ti-rich Ti₆₀Mo₁₀V₁₀C₁₀Zr₁₀ HEAs appeared to decrease remarkably. The alloying elements in the HEAs were locally present and no phase changes occurred even after additional HIP treatment. The lowest current density obtained in the polarization potential test of Ti-rich Ti₄₀Mo₁₅V₁₅Cr₁₅Zr₁₅ HEA was 7.12×10^-4 mA/cm² was obtained. The studied TiMoVCrZr HEAs showed improved corrosion characteristics as compared to currently available joint replacement material such as ASTM F75 alloy.