College of Graduate Studies: Theses & Dissertations

Term of Award

Spring 2026

Degree Name

Master of Science, Manufacturing Engineering

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Manufacturing Engineering

Committee Chair

Mingzhi Xu

Committee Member 1

JingJing Qing

Committee Member 2

Haijun Gong

Abstract

Shrinkage porosity is a major defect that significantly impairs the mechanical properties and overall performance of ductile iron castings. Although graphite formation during solidification induces volumetric expansion, this expansion alone is insufficient to fully compensate for the shrinkage occurring throughout solidification. During the solidification and cooling of ductile iron, multiple phase transformations occur, resulting in dynamic volume changes that exert pressure on mold walls and internal cavities. These pressures can deform mold walls and casting surfaces, leading to defects such as swell and porosity, while also influencing shrinkage formation. This study aims to analyze the mechanisms of porosity formation and to correlate the expansion and contraction behavior of ductile iron during solidification and cooling. Key process variables, including sprue height, risering conditions, pouring temperature, and carbon equivalent, are evaluated. A real-time wall movement measuring apparatus is used to monitor mold wall displacement during casting. In addition, density measurements are performed on different sections of the castings to quantify variations associated with porosity distribution. Image analysis of macro-porosity is conducted to evaluate porosity size and distribution, while scanning electron microscopy (SEM) is employed for detailed micro porosity characterization. Statistical analysis of the SEM data, including average graphite density and porosity density, is carried out to better understand the relationship between graphite precipitation and porosity formation. The combined experimental and analytical approach provides a comprehensive understanding of the factors influencing porosity in ductile iron castings.

Research Data and Supplementary Material

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