Effects of Thermal Treatment on Mechanical Properties of Recycled Aluminum Alloys

Thesis Abstract

The increasing demand for sustainable manufacturing practices has accentuated the importance of recycling aluminum alloys to mitigate environmental impacts and reduce reliance on primary aluminum sources. However, the mechanical properties of recycled aluminum alloys are often inconsistent due to variations in their microstructure, which are significantly influenced by thermal treatment processes. This study aims to systematically evaluate the effects of various thermal treatments—annealing, solution heat treatment, and aging—on the mechanical properties of recycled aluminum alloys, specifically focusing on 6061 and 7075 grades. The investigation seeks to determine the optimal thermal treatment parameters that enhance tensile strength, hardness, and ductility, thereby providing a pathway toward improved recycling protocols for aluminum alloys. The research adopts a quantitative, experimental research design structured to facilitate controlled laboratory investigations. The population comprises recycled aluminum alloys sourced from local scrap yards, with a total of 60 specimens prepared through standardized casting and processing procedures. A stratified random sampling technique is employed to allocate specimens into treatment groups. Data collection involves the use of advanced metallographic techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDX) for microstructural characterization, alongside mechanical testing methods such as tensile testing, Brinell hardness testing, and impact toughness assessments. Thermal treatments are conducted using a programmable muffle furnace with precise temperature control, following established protocols aligned with industrial standards. To ensure the reliability and validity of the measurements, calibration procedures are performed, and tests are replicated thrice per sample. Data analysis involves the use of descriptive statistics to summarize the mechanical properties, while inferential statistics—specifically two-way ANOVA—is utilized to examine the effects of different thermal treatment conditions and alloy grades on the measured properties. Regression analysis further explores the relationship between treatment parameters and mechanical performance. The theoretical framework integrates the precipitation hardening theory and recovery and recrystallization theories, providing insight into microstructural transformations driving property changes. Findings are anticipated to show that specific aging treatments significantly improve tensile strength and hardness without compromising ductility, and that extensive solution heat treatment enhances overall mechanical stability. Expected results include a detailed understanding of the microstructural changes induced by each thermal process, correlating these changes to measured mechanical properties. The study is projected to identify optimal treatment conditions for each alloy grade, contributing to the body of knowledge by elucidating the relationship between thermal treatment parameters and mechanical behavior in recycled aluminum alloys. Additionally, the research aims to fill existing gaps concerning the influence of combined thermal processes on recycled materials' structural and mechanical integrity, offering a comprehensive model to predict performance outcomes based on treatment variables. The main conclusion will affirm that tailored thermal treatment protocols can substantially improve the mechanical properties of recycled aluminum alloys, promoting their sustainable reuse in structural applications. Recommendations include adopting specific heat treatment cycles at industrial scales, promoting sustainable practices in aluminum recycling, and encouraging further research into environmentally friendly alloy processing techniques. The study also suggests further investigation into the fatigue life and corrosion resistance of thermally treated recycled alloys to expand the applicability of the research findings in real-world engineering contexts. Ultimately, this study contributes valuable empirical evidence for optimizing thermal processing techniques, thereby advancing sustainable metallurgical practices and enhancing the mechanical performance of recycled aluminum alloys in various engineering applications.