Evolution of interfacial microstructure and embrittlement mechanism in explosive-welded al/steel anode guide rod joints after high-temperature service

This study investigates in-service Al/steel explosive-welded joints retrieved from anode guide rods after two years of operation in an aluminum electrolysis cell. After prolonged service, the interfacial intermetallic compound (IMC) layer evolves from discrete islands into a continuous and homogenized brittle layer. While the average IMC thickness increases only slightly, from 87.8 μm to 93.5 μm, an increase of about 6.5%, the standard deviation decreases dramatically by about 60%, from 75.1 to 30.6, indicating that homogenization and continuity, rather than mere thickening, are key degradation features. After service, the continuous IMC layer is dominated by the Fe 4 Al 13 phase and contains voids and microcracks. Concurrently, the aluminum matrix undergoes significant grain coarsening, from 1.58 ± 1.19 μm to 2.82 ± 5.16 μm, an increase of about 78%, and softening evidenced by a 27.5% reduction in hardness. These evolutions lead to a 50.5% reduction in tensile strength and a transition from ductile fracture to brittle cleavage along the IMC layer. Two factors fundamentally cause the performance degradation: interfacial embrittlement from Al/Fe interdiffusion, and Al matrix softening. These findings provide a quantitative foundation for service life assessment and process optimization.