Forming Mechanism and Mechanical Properties of Carbon Nanotube Reinforced Aluminum Matrix Composites by Selective Laser Melting

Cast aluminum alloys have excellent casting and welding properties, but low hardness and poor wear resistance limit the range of applications, and fabrication of aluminum matrix composite parts is often an effective method. Carbon nanotube reinforced aluminum matrix nanocomposite parts（CNT/Al） are prepared by selective laser melting additive manufacturing technology. The densification behavior, phase, microstructure and mechanical properties under different laser energy densities（η） of as-fabricated specimens are investigated by setting various laser parameters. The relative density increases from 94.49% to 99.83% with increasing η from 150 J/m to 187.5 J/m. High laser energy density increases the size and the temperature of the molten pool, resulting in a decrease in the viscosity of the liquid and an increase in wettability, which leads to the uniform spreading of liquid phase. Besides, the degree of overlap between molten pools increases and the metallurgical defects such as pores reduced. As a result, the densification level increases. The main phases of as-fabricated specimens are Al9Si and Si, and the reaction of the outer layers of carbon nanotubes（CNTs） and the matrix generates Al4C3, which improves the interface stability. The hardness and wear resistance of as-fabricated specimens have a positive correlation with the relative densities. When η is settled at 187.5 J/m, the average microhardness of the specimen is 164.3 HV0.2, the coefficient of friction decreases to 0.21, and the strength and elongation are 452 MPa and 9.0%, respectively, showing excellent mechanical properties.