On the precipitation kinetics, microstructure evolution and mechanical behavior of a developed Al- Mn-Sc alloy fabricated by selective laser melting
Qingbo Jia, Fan Zhang, Paul Rometsch, Jitendra Mata, Jingwei Li, Matthew Weyland, Laure Bourgeois, Manling Sui, Xinhua Wu
The dynamic metallurgical characteristics of the selective laser melting (SLM) process offer fabricated materials with non-equilibrium microstructures compared to their cast and wrought counterparts. To date, few studies on the precipitation kinetics of SLM processed heat- treatable alloys were reported although such detailed knowledge is normally required for optimizing the mechanical properties. In this study, for the first time, the precipitation behavior of an SLM fabricated Al-Mn-Sc alloy was systematically investigated over the temperature range of 300 °C to 450 °C. The synergistic combination of in-situ synchrotron-based ultra-small angle X-ray scattering (USAXS), small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) revealed the continuous evolution of Al6Mn and Al3Sc precipitates upon isothermal heating in both precipitate structure and morphology, which was further confirmed by ex-situ TEM studies. A pseudo-delay nucleation and growth phenomenon of the Al3Sc precipitates was observed for the SLM fabricated Al- Mn-Sc alloy. This phenomenon was attributed to the pre-formed Sc clusters in the as-fabricated condition due to the intrinsic heat treatment effect induced by the unique layer-by-layer building nature of SLM. The growth kinetics for the Al6Mn and Al3Sc precipitates were established based on the in-situ X-ray studies, with the respective activation energies determined to be (73.9 ± 4.0) kJ/mol and (62.5 ± 9.0) kJ/mol. The role of the precipitate evolution on the final mechanical properties was evaluated by tensile testing, and an observed discontinuous yielding phenomenon was effectively alleviated with increased aging temperatures.