An Assessment of the Influence of Grain Refiners and Modifiers on The Performance Characteristics of Aluminum Alloy (AA-2618) Castings

Abstract

This study evaluates the influence of grain refiners and modifiers on the microstructure and mechanical performance of AA-2618 aluminum alloy castings. A titanium-based master alloy (Ti–Al) was employed as a grain refiner, while strontium chloride (SrCl₂) was used as a chemical modifier. Each additive was introduced at 0.12 wt%, both individually and in combination, to investigate their effects on grain structure, eutectic phase morphology, and the resulting mechanical properties. Cast samples were produced under controlled conditions and characterized using optical microscopy and standard mechanical tests, including Brinell hardness, tensile strength, impact energy, and percentage elongation. The results from Microstructural analysis revealed that SrCl₂ modification significantly altered the eutectic morphology and refined the solidification structure, resulting in an average grain size reduction of approximately 28–32% compared with the untreated alloy. This refinement translated into improved mechanical performance, with tensile strength increasing from 141.76 MPa to 169.92 MPa (≈19.9% improvement), elongation increasing from 3.99% to 5.56% (≈39.3% improvement), and impact energy rising from 2.55 J to 2.58 J (≈2% improvement). In contrast, the addition of Ti–Al grain refiner alone resulted in reduced tensile strength (112.90 MPa) and impact energy (2.33 J), attributed to the formation of coarse TiAl₃ intermetallic particles that acted as crack initiation sites. However, the combined Ti–Al + SrCl₂ treatment did not exhibit synergistic behavior and produced the lowest hardness (53.57 HB) and tensile strength (93.58 MPa), indicating competitive interactions that hindered effective grain refinement and modification. Overall, the results demonstrate that strontium-based modification offers the most effective approach for enhancing the microstructural integrity and mechanical performance of AA-2618 aluminum alloy castings.