Simultaneously enhanced strength and ductility of AlSi7Mg alloy fabricated by laser powder bed fusion with on-line static magnetic field

This work studied the effects of an on-line static magnetic field on the defects, microstructures, and mechanical properties of AlSi7Mg samples fabricated by laser powder bed fusion (LPBF). Process experiments were carried out on a self-developed LPBF equipment with an on-line static magnetic field generating system, where magnetic field intensity was adjustable from 0 to 0.3 T. With the action of static magnetic field, the relative density of samples increased from 96.9% to 98.6%. Furthermore, the solidification front of the columnar grain in the mushy zone was broken. With the increase of magnetic field intensity, the crystallographic orientation changed from strong <001> to <001>, <101> and <111> uniform distribution and the average grain was gradually refined from 8.35 to 7.22 μm. Based on the above optimisation, the ultimate tensile strength increased from (326.67 ± 5.31) MPa to (382.00 ± 2.45) MPa. Simultaneously, the elongation at break increased from 8.48% ± 0.20% to 11.78% ± 0.20%. In general, the reduction of pores, the refinement of grains and the increase of Mg2Si precipitates contributed to the simultaneous enhancement of strength and toughness together. This study could provide a new idea for laser additive manufacturing of excellent performance aluminum alloys.