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Additive Manufacturing of Dissolvable Aluminum Alloys

Baghi Ilkhechi, Ali | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58133 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahedi, Mojtaba
  7. Abstract:
  8. In the oil and gas industries, plugs made from dissolvable aluminum alloys are used for specific applications in oil and gas wells, including isolating different sections of the well and directing fracturing fluid to desired areas, for separating different sections of the well during production tests and collecting more accurate data, and for temporarily blocking the well during maintenance operations. These alloys corrode upon contact with an acidic or alkaline solution, as well as through the formation of galvanic cells with secondary particles such as tin, zinc, and silver compounds. Currently, these types of alloys are mainly produced using casting methods. However, due to the presence of elements such as tin, zinc, and copper in these alloys, and the macroscopic and microscopic segregation of these elements during alloying and casting, controlling and ensuring the uniformity of their chemical composition is challenging. This is because the segregation of these elements leads to a heterogeneous structure, resulting in varying dissolution rates, physical properties, and mechanical properties in different parts of the components produced from these alloys. Utilizing the Wire Arc Additive Manufacturing (WAAM) process, due to its layer-by-layer fabrication of a part, can reduce the problem of macroscopic and microscopic segregation of alloying elements. In this research, a dissolvable Al-Sn-Mg-Cu-Ag alloy was fabricated using the Gas Metal Arc Welding (GMAW) additive manufacturing process with varying heat inputs. Walls with approximately 30-60 layers were produced at welding speeds of 1, 2, and 5 mm/s for different heat inputs. The results showed that this method was successful for macroscopic segregations, but microscopic segregations, especially in the sample produced at a welding speed of 1 mm/s, were observed. By increasing the heat input (decreasing the welding speed), the porosity decreased from 3.00% to 1.13%. In all samples, columnar grains and equiaxed dendritic structures were observed in the microstructure in two forms. Columnar grains formed due to high temperature gradients and low growth rates, while equiaxed grains formed by detaching from the solidification front due to the fact that undercooling increases with distance, and consequently, with a decrease in G/R. In this process, the sample produced at a welding speed of 5 mm/s had the smallest grain size due to the high welding speed and low heat input, resulting in a high cooling rate. It was found that the aluminum matrix contained precipitates and secondary phases of Al2Cu, Mg2Sn, and MgZn2. With increasing heat input, the precipitates became discontinuous, and tin segregation occurred more heterogeneously. The maximum tensile strength of the produced walls was investigated in two directions: parallel to the build direction and perpendicular to the build direction (parallel to the deposited layers). Among the samples parallel to the build direction, where strength depends on interlayer bonding and porosity, the highest strength of 125 MPa was achieved for the sample produced at a welding speed of 2 mm/s. Among the samples perpendicular to the build direction, where strength depends on the formed precipitates, the highest strength of 193 MPa was achieved for the sample produced at a welding speed of 5 mm/s. The dissolution capability of the samples was also investigated by immersing them in a 5% KCl solution for 1 hour at 90°C and then for 24 hours at room temperature. It was observed that the best sample in terms of dissolution was the one produced at a welding speed of 2 mm/s, which, due to its continuous and fine precipitates, exhibited dissolution rates of 150.33 and 0.74 mm/year at 90°C and room temperature, respectively
  9. Keywords:
  10. Wire and Arc Additive Manufacturing ; Microstructure ; Macroscopic Segregation ; Mechanical Properties ; Heat Input ; Dissolution Rate ; Dissolvable Aluminum Alloys

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