Comparative Analysis of Additive vs. Conventional Casting in Al Alloys

Thesis Abstract

This study addresses the growing need to understand how additive manufacturing–based casting processes compare with conventional casting for aluminum alloys in terms of microstructure, mechanical properties, and manufacturability under industrial conditions. The problem centers on inconsistent performance of Al alloy components produced by additive versus traditional methods, with implications for reliability, weight reduction, and cost. The aim is to systematically evaluate and contrast the microstructural evolution, defect content, mechanical responses, and process efficiencies of selected Al alloys subjected to additive casting (directed energy deposition and powder bed fusion-derived casting) and conventional sand and chill casting. Specific objectives are to characterize grain structure, precipitate distribution, porosity, and residual stress using electron backscatter diffraction (EBSD), X-ray computed tomography (XCT), and neutron diffraction; to quantify tensile, fatigue, creep, and hardness properties under standardized test conditions; to assess surface finish, dimensional accuracy, and defect mechanisms via scanning electron microscopy (SEM) and surface profilometry; to evaluate process economics, energy consumption, and cycle times through a life-cycle assessment and time-motion analysis; and to develop predictive models linking processing parameters to mechanical performance using regression analysis and analysis of variance (ANOVA). The population comprises industrially relevant Al alloys (such as Al–Si–Mg 356, Al–Zn–Mg 7xxx series, and Al–Cu 2024) produced by both additive and conventional casting routes. A stratified random sampling approach selects 60 specimens per alloy system, with equal representation across processing methods, heat treatments, and orientation. Data collection instruments include EBSD, XCT, SEM, Vickers hardness testers, universal testing machines for tensile and fatigue testing, nanoindentation for local mechanical properties, and calorimetric and energy-monitoring devices for process energy data. Validity and reliability are ensured through calibration protocols, repeat measurements, and inter-laboratory cross-validation for a subset of samples. The analysis employs descriptive statistics, multivariate ANOVA to compare microstructural and mechanical outcomes across methods, regression models to relate process parameters to properties, and response surface methodology to optimize casting conditions. A theoretical framework integrates materials science theories of heterogeneous nucleation, grain growth models, and precipitation kinetics with design-for-manufacturability concepts, supported by the Theory of Materials Processing and the Resource-Based View for economic assessment. The conceptual model links additive casting parameters (laser power, scan speed, layer thickness, cooling rate) and conventional casting variables (mold material, cooling rate, pouring temperature) to defect metrics (porosity, cold shuts), microstructure (grain size, texture, precipitate distribution), and properties (tensile strength, yield strength, elongation, fatigue life). Expected findings indicate that additive casting can achieve finer grain structures and more uniform precipitate distributions with lower porosity in high-Si Al alloys but may exhibit anisotropic properties due to directional solidification; conventional casting is anticipated to deliver superior surface finish and dimensional accuracy in certain geometries but with higher porosity risks in complex cores. The study is anticipated to reveal statistically significant differences in high-cycle fatigue performance and fracture toughness, with nuanced performance dependent on alloy system and post-processing. The contribution to knowledge includes a rigorous, comparative evidence base for selecting processing routes for Al alloy components, development of predictive models tying processing to performance, and a framework for integrating additive casting into industrial design with quantified trade-offs. The study concludes with recommendations for processing guidelines that optimize mechanical performance while minimizing cost and environmental impact, and suggests lines for future research on hybrid casting approaches, post-treatment strategies, and lifecycle assessment across broader alloy systems.