Electronic Theses and Dissertations

Date

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Committee Chair

Ebrahim Asadi

Committee Member

Gladius GL Lewis

Committee Member

Gary GB Bowlin

Committee Member

Amir AH Hadadzadeh

Committee Member

Reza RM Molaei

Abstract

ABSTRACT Attarzadeh, Faridreza, Ph.D., The University of Memphis, October 2022, Dissertation title: Laser-based powder bed fusion manufacturing of WE43 magnesium alloy and binary magnesium-calcium alloys Magnesium (Mg) and its alloys are a unique class of hard-to-process yet critical lightweight engineering materials. Over the years, there have been many developments that address the limitations of the various conventional manufacturing methods used to fabricate Mg- based parts, the latest being additive manufacturing (AM) methods, notably laser powder bed fusion (L-PBF). Despite a few successful attempts with non-L-PBF processes, L-PBF is increasingly gaining in popularity and importance for AM of Mg and its alloys. The focus of the three studies presented in this dissertation is L-PBF of Mg-based alloys. The purpose of the first study was to provide a comprehensive and critical review of the literature on the optimization of processing parameters used in the L-PBF processing of Mg and its alloys, post-processing methods applied to the as-built parts, and corrosion and degradation behaviors of the parts compared to corresponding results when parts are fabricated using conventional manufacturing methods. This critical review also includes suggestions for future research work and concludes with a summary of the key points made in the present study. It is well known that L-PBF processing of Mg and its alloys is associated with high Mg loss due to vaporization (MgLoss) and high incidence of many types of defects in the manufactured parts/samples. Despite this, Mg loss, densification, and defect characteristics have not been holistically considered in the determination of the optimal values of L-PBF processing parameters for Mg and its alloys. In the second study, a combined modeling and experimental approach was applied to a widely used Mg alloy (WE43) to address this shortcoming of the literature. Use of the optimal values of L-PBF processing parameters obtained in the study resulted in 0.23 wt% MgLoss for WE43 Mg alloy, whereas earlier studies reported MgLoss values that are about an order of magnitude higher than this. Furthermore, more than 99.5% densification is achieved while only ~2% and ~0.5% of the total defects are characterized as keyhole and lack of fusion defects, respectively. The third study investigated the manufacturability of MgCa10 alloy through L-PBF processing. A wide range of commonly used processing parameters was tested to investigate the manufacturability of this alloy. It was found that this alloy suffers from hot tearing and formation of keyhole defects, and even the high cooling rate or rapid solidification conditions of L-PBF process cannot solve these issues. It was also found that hot tearing susceptibility of the alloy can be reduced with the reduction of the size of the sample. An energy density range between 30 and 60 J/mm3 was identified as the forming range for L-PBF processing of this alloy. The observed microstructure had a smaller amount of a eutectic phase (8%) and was much finer when compared to the cast alloy.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest

Notes

Embargoed until 11/2/2024

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