Study on in situ laser shock modulation of molten pool and defects in wire-feed laser additive manufacturing of steel to aluminum alloy

A method was proposed to address the porosity defects and intermetallic compound production during laser additive manufacturing in dissimilar metals by employing in situ laser shock modulation of molten pool in a hybrid additive manufacturing process. Using wire-feed laser additive manufacturing directed energy deposition technology, single-layer and multi-layer thin-walled samples were prepared. The modulation of molten pool and porosity defects in single-layer molten tracks was analyzed under different pulsed laser shock energies. The mechanism of in situ laser shock modulation of molten pool was investigated through experiment and numerical simulations. The findings indicate that the shock force is the main factor causing oscillating convection in the molten pool, thereby accelerating Marangoni convection, bubble overflow, and pore closure. A pulsed laser shock energy of 2 J resulted in the optimal interface between the aluminum alloy and stainless steel. This interface exhibited a desirable molten track feature size, achieved a maximum densification of 99.73 % and an ultimate tensile strength of 140.25 MPa. Furthermore, in situ laser shock modulation of molten pool has the potential to reduce porosity defects and enhance microhardness, the number of porosity defects decreased by approximately 53.51 % and the total volume of porosity defects decreased by approximately 50.09 %, and microhardness approximately enhanced by 7.86 % at 2 J. Consequently, this method is anticipated to be implemented in the joining of critical thin-walled components to reduce defects and enhance tensile performance.