Mitigation of pores generation at overlapping zone during laser cladding

• Power density decreased suddenly at overlapping zone generated pores.
• Distribution of power density depends on width-to-height ratio of single track.
• The critical width-to-height ratio is influenced by power density of laser.
• A bad metallurgical bond and contraction of molten pool generated flat pore.

In the process of laser cladding, pores existing frequently at the bottom of overlapping zone. The generation mechanism and controlling methods of the pores are investigated. The results showed that the laser power density suddenly decreases at the bottom of overlapping zone because of the tangential angle of the cladding outline, and the lower power density slowed down the generation of the molten pool. On the other hand, the molten pool around the border position formed quickly and fused together. Then the pores formed due to the rapid solidification of the molten pool. The main factor that affects the generation of pores is the width-to-height ratio of single track because it affected the power density by the angle indirectly. Besides, a higher power density and lower thermal conductivity can restrain the generation of the pores by increasing convection intensity and convection time of the molten pool. In addition, reducing the high-melting-point hard phase may lead to smaller pores.