The impact of solution time on the microstructure and properties of NiTip/6061 Al matrix composites fabricated by hot pressing and extrusion

Abstract

This study investigates the impact and underlying mechanisms of solution time on the microstructure and mechanical properties of NiTi particle-reinforced 6061 Al composites. The findings indicate that significant alterations occur in the interfacial reaction phase of the composites following treatment with varying solution times. As the solution time increases, the thickness of the interfacial reaction phase progressively increases. Furthermore, the interfacial reaction phase develops a double-layer structure, consisting of the AlTiSi phase that tightly surrounds the NiTi particles and the discontinuously distributed Al₃Ni phase. The exceptional tensile strength and elongation characteristics of the 6061 Al alloy are attained following a 6-min solution treatment, after which these properties remain relatively stable. The NiTi_p/6061 Al composites demonstrate their peak tensile strength of 380 ​MPa and elongation of 17.1 ​% subsequent to a 30-min solution treatment; however, both tensile strength and elongation exhibit a decline thereafter. The fracture surface of the composite reveals prominent toughness dimples, with portions of the Al matrix adhering to the surfaces of the NiTi particles. This observation indicates a robust bonding relationship between the Al matrix and the NiTi particles, which can be attributed to the uniform distribution of the AlTiSi phase. Beyond a solution treatment duration of 30 ​min, the toughness dimples on the fracture surface diminish, and the Al matrix adhering to the NiTi particle surfaces gradually decreases due to the development of an increasingly uneven and coarse Al₃Ni interface reaction phase as the solution time is extended.