Semester of Graduation
Fall 2025
Degree
Master of Science (MS)
Department
Mechanical and Industrial Engineering
Document Type
Thesis
Abstract
Additive friction stir deposition (AFSD) is an emerging solid state additive manufacturing (AM) technique that offers many advantages over conventional fusion-based methods such as laser powder bed fusion and direct energy deposition. Since the material does not melt in AFSD, solidification related defects such as hot cracking, porosity, and residual stresses do not generally present in this process. Therefore, AFSD enables processing of materials that are considered non-weldable or highly challenging to process using fusion-based AM. Despite these advantages, research on AFSD is still relatively limited and successful deposition of high-strength and precipitation-hardened aluminum alloys such as Al 7075 is challenging. In the present study, a set of processing parameters for the AFSD of Al 7075 was introduced to fabricate defect-free parts. The as-deposited samples were then characterized to evaluate their microstructure, electrical conductivity, and mechanical properties. The results indicated that the hardness and tensile strength significantly dropped from 176.5 HV and 551.6 MPa to 80.4 HV and 311.7 MPa, respectively after the process. In contrast, the electrical conductivity improved by approximately 19.5% compared to the feedstock. Microstructural investigation revealed that although the grains were significantly refined during AFSD due to the severe plastic deformation, the strengthening precipitates were larger and non-uniformly distributed which led to the reduction in the strength and hardness and enhancement in the conductivity. To adjust the microstructure and recover the mechanical properties, T73 heat treatment was performed to the as-deposited Al 7075 specimens. The thermal treatment dissolved the coarse precipitates back into the matrix and led to the nucleation of fine, uniformly distributed secondary phases during artificial aging. As a result, the mechanical performance significantly recovered: hardness improved by 101.5% % and tensile strength increased by 49.1% relative to the as-deposited part. Additionally, the conductivity decreased by 6.8%. These changes indicated that heat treatment was essential for optimizing the performance of the Al 7075 parts prepared by AFSD. Overall, this study demonstrates successful application of AFSD to fabricate high strength Al alloys and establishes the process–microstructure–property relationships.
Date
11-24-2025
Recommended Citation
Bagheri, Ehsan, "ADDITIVE MANUFACTURING OF AL 7075 BY FRICTION STIR DEPOSITION: MICROSTRUCTURE MODIFICATIONS AND MECHANICAL PROPERTIES ENHANCEMENT VIA HEAT TREATMENT" (2025). LSU Master's Theses. 6239.
https://repository.lsu.edu/gradschool_theses/6239
Committee Chair
Shengmin Guo
Student Approval Forms
Included in
Aerospace Engineering Commons, Materials Science and Engineering Commons, Mechanical Engineering Commons