In-situ monitoring and metallographic observations of mass transfer and defect formation during AlSi10Mg additive manufacturing using powder sheets

Metal additive manufacturing using powder sheets (MAPS) melts powder attached in a sheet with a polymer binder, avoiding risks of loose powders in material waste, safety and health during laser additive manufacturing among other for e-mobility applications. However, this concept remains challenging for aluminum alloys due to occurring defects. To address this challenge, the mass transfer and defect formation mechanism during MAPS-AlSi10Mg were investigated using high-speed imaging and metallographic observations. The results showed that the mass transfer is realized via droplets formed first from the powder sheet in front of the melt pool and their incorporations into the melt pool. However, a much laser defocusing significantly inhibits the droplets’ incorporation into the melt pool and promotes the balling. Polymer coatings or it wrapped into the AlSi10Mg droplets, generates the inclusions once the droplets were incorporated into the melt pool. Furthermore, under the laser beam in focus, the large particle-size powder sheet, powder side up or low scanning speed easily induce pores via shielding gas/polymer vapor inclusion. The laser defocusing of +15 mm, average laser intensity of 1.6×105 W/cm2, and binder side up induce defect-free tracks, owing to the complete removal of polymers by their sufficient evaporation and powder agglomeration spatters. This work unveils that the droplets’ incorporation into melt pool leads to the mass transfer of MAPS-AlSi10Mg while the droplets containing polymers and gas/vapor inclusion generate inclusions and pores. Meanwhile, the defect-free production strategy of suitable defocusing and high laser intensity is proposed.