Effect of defocus manner on laser cladding of Fe-based alloy powder

• The beam of parallel Gaussian laser through a focusing lens has been simulated.
• Negative defocus is applied to solve the problem of high dilution rate and pores.
• Microstructure and microhardness of composite coating have been analyzed.

This investigation was focused on the influences of defocus manner and composite powders on laser cladding. Combining with the transmission characteristic of parallel Gaussian laser beam through a focusing lens, the energy distribution of the cross section of the laser beam in positive and negative defocused zone was analyzed and also verified by laser dotting ablation. Comparing with positive defocus, the negative defocus is an effective way for high quality laser cladding providing more advantages. Therefore, the negative defocus method is selected to solve the problem of high dilution rate and pores in the overlapping coating. The study showed that by adjusting the process parameters, a coating with low dilution and free of pores can be achieved easily in the negative defocus. Finally, the microstructure and microhardness of Fe-based alloy mixed with 5 wt.% Cr3C2 coating were analyzed.