Influence of additive multilayer feature on thermodynamics, stress and microstructure development during laser 3D printing of aluminum-based material

A transient three dimensional model for describing the temperature behavior, thermo-capillary convection, microstructure evolution and the resultant mechanical properties during selective laser melting of AlN/AlSi10Mg composite is proposed. The powder-solid transformation, temperature dependent physical properties and the preservation of the heat are taken into account. The effect of the additive manufacturing multilayer feature on the molten pool dynamics, cooling rate, crystal size, microstructure morphology, micro-hardness and types of the residual stress has been investigated. It shows that the operating temperature and the thermo-capillary convection obtained within the molten pool generally increases as the processing multilayers are successively added, while the thermal effect depth is negatively reduced. The preferential direction of the heat diffusion generally changes from a downward pattern, then to the slightly strengthened horizontal direction and finally to a typically horizontal one for various deposited layers being processed. Therefore, the microstructure of the solidified part along the building direction (Region I to Region V) undergoes an interesting transformation: directional columnar cellular microstructure, crosswise-extended cellular microstructure, refined cellular microstructure, fragmentation microstructure and the coarse cellular microstructure. The tensile stress and the compressive stress are comprehensively obtained within the finally solidified layers, significantly influencing the microhardness. (C) 2017 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.