Iranian Research Organization for Science and Technology Journal of Particle Science and Technology 2423-4087 11 2 2026 01 05 Effect of Zr particles and RRA heat treatment on properties and grain boundary precipitation of 7055 Aluminum alloys 93 100 1644 10.22104/jpst.2026.7865.1287 EN Mehdi Shakoory Advanced Materials and New Technology Department, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran Mohammad Esmailian Advanced Materials and New Technology Department, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran Morteza Taheri Advanced Materials and New Technology Department, Iranian Research Organization for Science and Technology (IROST), Tehran, Iran Journal Article 2025 11 16 Due to its high strength and corrosion resistance, aluminum alloy 7055 is widely used in aerospace structures. However, its susceptibility to stress corrosion cracking (SCC) limits its performance. In this study, the combined effects of zirconium (Zr) addition and retrogression and re-aging (RRA) heat treatment on the microstructure, grain boundary precipitates, and stress corrosion resistance (SCR) of 7055 aluminum alloy were investigated. For property evaluation, microstructural characterization was carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), while mechanical and stress corrosion tests were conducted according to ASTM standards. The results showed that Zr addition refined the grains and promoted the formation of Al₃Zr particles within the matrix, inhibiting grain growth during heat treatment. RRA treatment accompanied by Zr addition improved the mechanical strength from 528 to 608 MPa and increased the stress corrosion resistance from 68 to 96 %. The combined effect of Zr addition and RRA treatment resulted in a more stable microstructure, with improved strength and resistance to stress-corrosion cracking. https://jpst.irost.ir/article_1644_89f03f7d02720160f1b04cf5b27f5ccb.pdf