横向静磁场对激光熔化增材制造Al-12%Si合金凝固组织的影响

Due to the great advantage in manufacturing component with complex structures, additive manufacturing (3D print), essentially the rapid solidification of tiny metallic molten pool (hemisphere like with diameter ranging from dozens of microns to several millimeters) has become an important formation technique. Using powder laser melting, the effect of transverse static magnetic field on the solidified structure of additive manufactured Al-12%Si alloy was studied. The macrostructure was formed by white band (mainly primary α-Al phase) and dark grey area (mainly eutectic phase) and no obvious influence was presented with or without static transverse magnetic field of 0.35 T. However, for the microstructure, the primaryα-Al in dark grey area formed as columnar structure without magnetic field was found to transform to dendritic like with developed dendrite arms when under a static transverse magnetic field. The analysis on thermoelectricity and dimensionless Hartman parameter which used to characterize the restriction of static magnetic field on molten flows show that under a static transverse magnetic field of 0.35 T, the thermoelectric magnetic force can be as high as a magnitude of 10⁵ N/m³, and Hartman values is far more than 10. The results indicate that the Marigoni and thermosolutal convection in laser melting pool was restricted. The transform from columnar to equiaxed dendrite of primary α-Al in dark grey area under static magnetic field was attributed to the fragmentation by thermoelectric magnetic force (10⁵N/m³) in solid phase. In addition, the formation of high order dendrite arms was supposed to be caused by the restriction of static magnetic field on the melt.