Laser additive manufacturing (LAM) is a novel technology that uses high-energy laser beam to obtain high performance entities and coatings. However, in this process, it is difficult to control the microstructure of materials effectively by changing the laser parameters. Based on this situation, we proposed a method that using direct electrostatic field (DESF) to assist LAM process. In this paper, we investigated the changes in 316L microstructure after assisted by DESF, and discuss the effect of electrostatic field. Microstructures of the 316L stainless steel sample fabricated by this method were tested. The result showed the solidification direction and grain morphology was influenced by the direction and value of DESF obviously. While the ESF direction is opposite to the laser scanning direction, the grains in the longitudinal-section perform orderly growth and the directions are biased to the laser scanning direction. While the DESF direction is the same as the scanning direction, the original solidification direction is obviously changed and the direction tended to be opposite to the scanning direction.
With the lightening tendency in the automobile and aircraft industry, the aluminium (Al) alloy and the carbon fiber reinforced thermal polymer (CFRTP) has been widely used. The CFRTP component always needs to be joined with Al alloy to form a CFRTP/Al alloy composite structure. Due to the large differences in the physicochemical properties of CFRTP and Al alloy materials, it is difficult to join with each other. Laser stir welding technology was applied to join CFRTP and Al alloy dissimilar materials in this research. In order to improve the CFRTP/Al alloy joining strength, a surface pre-treating method (laser micro-engraving) was proposed in this paper. Three micro-scale structures were designed and prepared on 7075 Al alloy by surface laser micro-treatment, which are linear grooves, mesh grooves and circular grooves. The morphology and dimensions (width and depth) of the microstructure on the strength of CFRTP / Al alloy joints were studied. The interface morphology and the fracture morphology of the joint were observed by the laser confocal microscopy and the scanning electron microscopy (SEM). Furthermore, the joining mechanism and failure mechanism of the CFRTP/Al alloy joint were explored. The results indicated that the microscale structures play an important role in improving the mechanical properties of Al alloy and CFRTP joins under different laser micro-engraving.
AlCrFeMnNi high-entropy alloy was prepared by laser additive manufacturing with gas-atomized pre-alloy powders. The phase, microstructure and microhardness of HEA have been investigated. The HEAs without electric field controlled and under controlled were composed of single BCC phase. Under the controlling of electric field, the pores presented the phenomenon of reducing. Due to the reducing of pores, the HEA under electric field controlled became harder and exhibited high microhardness of about 529.9 HV0.2, which was 6.49% higher than the HEA without controlled.