Tailored formation of novel reinforcement in laser additive manufactured aluminum matrix nanocomposites and its strengthening mechanisms on mechanical properties

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One of the significant drawbacks for ceramic particle reinforced aluminum matrix composites (AMCs) is the decrease of ductility accompanied with the increase in strength. Decreasing the size of reinforcement to nanoscale is a promising approach to solve the contradiction between strength and ductility of AMCs. In the present project, powder-based laser additive manufacturing (LAM) processes including selective laser melting (SLM) and laser metal deposition (LMD) are applied to process Al-based nanocomposites through a complete melting and solidification mechanism. The unique feature of LAM of high heating and cooling rates and resultant non-equilibrium metallurgical mechanism are considered, in order to realize the controllable development and dispersion of re-precipitated nanoscale ceramic reinforcement. This project theoretically studies the temperature, velocity, and solute fields and their combined effect on the growth and dispersion of nanoscale ceramic reinforcing phases within laser-induced molten pool under the action of non-equilibrium Marangoni flow, thereby proposing the laser-controlled formation mechanisms of nanoscale reinforcing phases with unique microstructure and distribution features. The influence of the category and contents of reinforcing ceramics and Al-matrix, the physical properties of powder, and the applied laser processing parameters on the crystallization and growth behaviors of nanoscale ceramic reinforcing phases is quantitatively studied, in order to propose the material and process methods to obtain the controllable microstructures of nanoscale reinforcement. The mechanical properties (especially tensile strength and ductility) of laser additive manufactured AMCs parts are studied and the underlying strengthening mechanisms of nanoscale reinforcement to Al-matrix are elucidated. A process¿microstructure¿performance relationship is accordingly established to enable the successful production of AMCs parts with tailored reinforcement architecture and improved mechanical performance. The integration of 'designed material', 'tailored process', and 'controllable performance' is emphasized in this project, providing the scientific theoretical basis and key strategy for LAM of high-performance AMCs components.