Ageing behaviour of polymer-metal joints produced by additive manufacturing

The long-term durability of dissimilar material joints is critical for a wide range of engineering applications, where hybrid structures are increasingly produced by additive manufacturing. However, the effects of ageing on these joints remain insufficiently explored. Given that polymers and metals undergo different degradation mechanisms when exposed to environmental factors, understanding their interaction is essential. PLA and Al were employed as representative polymer-metal materials to evaluate the influence of temperature-driven ageing on the mechanical and structural stability of PLA-Al joints produced by fused filament fabrication. The research focuses on understanding the impact of prolonged exposure to different temperatures on the mechanical performance and structural integrity of the joints over time. This is achieved by conducting mechanical testing and microscopic, thermal and chemical analysis, evaluating changes in joint strength and deformation. The results demonstrate that prolonged exposure to high temperatures significantly accelerates degradation, promoting microvoid formation, interlayer separation, and a reduction in tensile strength, leading to structural failure. In contrast, moderate and lower temperatures slow the degradation process, preserving over 75–80% of the initial joint strength after 90 days. Despite PLA’s known susceptibility to degradation, an acceptable service window exists under moderate and low thermal conditions. Moreover, hybrid joints exhibited improved mechanical retention compared with aged polymer specimens under the same conditions. These findings define practical service limits for biodegradable polymer-metal joints and provide new insight into their temperature-dependent ageing behaviour, supporting the design of hybrid structures with predictable and controlled durability.