Flow stress modeling and microstructural evolution during hot compression of Al-4.8Mg-0.3Sc alloy produced by laser powder bed fusion

The present work aims to study the influence of hot deformation on microstructural development and flow behavior in the Al-4.8Mg-0.3Sc alloy produced by the laser powder bed fusion (LPBF) technique. Uniaxial compression tests have been conducted within a temperature regime of 200–350 ºC at a 0.01–1 s−1 strain rate using a Gleeble-3800™ thermomechanical simulator. The major results show that the flow behavior is governed mainly by strain hardening at 1 s−1 strain rate and dynamic recrystallization (DRX) at 0.1 s−1 within 250–350 ºC. The constitutive equations have been developed by employing activation energy (Q) and other material constants to forecast the influence of deformation temperature and strain rates on flow stress. Compared to other Al alloys (114–227 kJ/mol), the mean Q for hot deformation is found to be significantly higher (∼340 kJ/mol at a 0.69 true strain), indicating more stress requirement for deformation, also confirmed by the flow curves. Moreover, the processing map developed with MDMM+Poletti instability criteria is found to be appropriate compared to DMM and MDMM models. The safe workable zone is obtained in the range of 250–350 ºC/0.01–1 s−1 with a maximum power dissipation efficiency of 45.8 %. Microstructural analysis shows that recrystallization starts primarily at melt pool boundaries which formed during the LPBF process. The highest recrystallization fraction is observed for the specimen deformed at 350 ºC/0.01 s−1 (59.3 %). SEM analysis of the samples deformed at 200 ºC/0.01–1 s−1 and 250 ºC/1 s−1 depict the formation of various defects, such as voids and micro-cracks, mainly governed by the non-uniform deformation at the particle/matrix interface and due to the presence of voids/pores. A detailed investigation of Q, stress exponent (n), flow stress behavior, and constitutive equations suggests that the hot deformation is mainly governed by both dislocation climb and cross-slip mechanisms. [Display omitted] •Uniaxial compression tests were conducted in Gleeble-3800 thermomechanical simulator.•Flow behavior is governed by dynamic recrystallization for 0.1 s−1 strain rate at 250–350 °C.•The mean Q value for hot deformation is found to be ∼340 kJ/mol at a 0.69 true strain.•MDMM+Poletti instability criterion is more appropriate than DMM and MDMM models.•Hot deformation is mainly governed by dislocation climb and cross-slip mechanisms.