Abstract:

Understanding the influence of heat treatment on microstructure and local mechanical performance is critical for the reliable application of aluminum-iron bronze (Al-Fe bronze) in marine and aerospace industries. While these structure-properties relationships have been extensively studied in conventionally manufactured Al-Fe bronze, they remain relatively unexplored in additively manufactured (AM) counterparts. Wire arc additive manufacturing (WAAM) presents a cost-effective method for fabricating large-scale Al-Fe bronze components, offering reduced material waste and improved production efficiency compared to traditional manufacturing routes.

In this study, the effects of two key heat treatment parameters – annealing temperature and annealing time – on the microstructure and mechanical properties of WAAM-fabricated Al–Fe bronze were systematically investigated using response surface methodology-central composite design (RSM-CCD). Quadratic response models were successfully developed to predict Vickers hardness and nano-hardness as functions of annealing temperature and time. The optimal heat-treatment condition was identified as 450^oC for 3.5 hours, yielding Vickers hardness and nano-hardness values of 112 HV₁₀ and 3.3 GPa, respectively.

Microstructural analysis indicated significant heat treatment-induced modifications, including grain refinement, reduced crystallographic misorientation and dislocation density, and increased fractions of high-angle grain boundaries (HAGBs) and annealing twins. These microstructural changes contributed to enhanced hardness and elastic modulus of the Al-Fe bronze alloy. Overall, this study highlights the effectiveness of an RSM–CCD-based optimization approach in tailoring heat treatment to improve the performance of WAAM-fabricated Al-Fe bronze components, thereby enhancing their suitability for demanding marine and aerospace applications.

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Mr. Ahmed Aliyu