Study On The Process And Strengthening Mechanism Of SiC Particle Reinforced Aluminum Matrix Composites By Selective Laser Melting

Silicon carbide particle?SiCp?reinforced aluminum matrix composites?AMCs?have been widely used in automotive,marine,aerospace and other fields known for its high specific strength,high specific modulus,small thermal expansion coefficient and excellent thermal conductivity.Due to the large difference in physical and chemical properties between the reinforcing phase particles and the aluminum matrix material,the conventional process for preparing the SiCp-reinforced AMCs cannot effectively wet the reinforcing phase,so no effective interface bond is formed between the aluminum matrix and the reinforcing phase,which seriously affects the performance of the SiCp-reinforced AMCs.Selective Laser Melting?SLM?based on discrete and stacking principles uses high-energy laser beams as a heat source to create metal parts through“bottom-up”material accumulation,significantly shorten production cycles and reduce manufacturing costs,its unique rapid heating and cooling process provides the possibility to produce SiCp reinforced AMCs with high mass fraction and excellent mechanical properties.In this paper,the process of melt forming SiC?10 wt.%?/AlSi10Mg composite by laser is selected as the object.Firstly,the influences of forming parameters such as laser power,scanning speed and scanning pitch on the density of SLM-formed aluminum matrix composites were studied.The causes of porosity and spheroidization in the forming process,the phase composition,microstructure,mechanical properties of SiCp reinforced aluminum matrix composites and the relationship between them and linear energy density at the optimal process parameter window were clarified.Secondly,the characteristics of the molten pool and temperature field in the process of SLM forming SiCp reinforced AMCs were studied by numerical simulation.The formation mechanism of the reinforcing phase and microstructure and the strengthening mechanism of the materials were revealed.The results show that the optimal process window for SLM forming 10 wt.%SiCp reinforced AMCs:laser power P is 300 W³10 W,scanning speed V is 800 mm/s¹000mm/s,and scanning pitch D is 0.12 mm,the layer thickness is 30?m.The SiC particles have little influence on the fluidity of the melt in the molten pool when the process window is formed,the molten pool has good stability,the in-situ reaction between SiC particles and molten aluminum matrix is relatively complete,and the reinforcing phase is distributed more uniform in the aluminum matrix,SiCp reinforced AMCs with high density and excellent performance can be obtained.The numerical simulation of the size of the molten pool shows a high consistency with the experimental measurements.The size and temperature of molten pool of SiCp reinforced AMCs increase with the increase of laser linear energy density.The maximum size of the molten pool is 219,168 and 114.23 microns,the maximum temperature of the molten pool is 1867.02?.The phase of SLM formed SiCp reinforced AMCs consists of?-Al phase,SiC phase and Al₄SiC₄ phase.The SiCp and Al₄SiC₄ particles and the elastic distortion caused by Si atoms and Al hinder the dislocations moving on the slip surface and produce dispersion strengthening and solid solution strengthening on the matrix,the stress is transferred from the matrix to the strip-shaped Al₄SiC₄ reinforcement to form a direct reinforcement,fine grain size in the formed sample leads to an increase in grain boundary area and fine grain strengthening.Under the synergistic effect of the above four strengthening mechanisms,the process parameter has laser power of 300 W,scanning speed of 800 mm/s,and linear energy density of 104.16 J/mm³,the formed specimens have the most excellent mechanical properties,the microhardness is between205 and 215 HV0.1 and the fluctuation is gentle,the tensile strength,yield strength and elastic modulus are 441.8 MPa,381.4 MPa and 84.2 GPa,respectively,which are increased by 15.7%,46.7%and 20%respectively compared with the tensile strength,yield strength and elastic modulus of the matrix Al alloy.Meanwhile,the fracture mechanism of SLM SiCp reinforced AMCs is brittle fracture.The above study on the process and strengthening mechanism of selective laser melting and forming SiCp reinforced AMCs established the relationship between the process parameters,microstructure and mechanical properties,which laid a foundation for further exploring the process parameters of SLM formed SiCp reinforced AMCs.