Study On FE-Al Composite Coatings In Laser Cladding And Numerical Simulation

Laser cladding, a new surface modification technology, could improve the surface hardness, wear resistance and corrosion resistance of materials. Therefore, it has been widely used in aerospace, machine, electricity, petroleum, automobile, military and so on.Fe-Al composite coatings were prepared on the surface of Q235 steel by laser cladding with the powder preplaced and the temperature and stress fields of Fe-Al composite coatings were simulated by ANSYS software in this paper. The microstructure and phase of Fe-Al composite coatings were investigated by means of XRD and SEM methods and the hardness and wear resistance of cladding layer were studied.The simulation results show that the temperature distribution is dynamic and in an oval shape. There is larger temperature gradient in cladding layer, up to 106K/m magnitude. The interface temperature and the pool depth of substrate are rising with the increase of laser power, and decreasing with the increase of scanning speed. The Von Mises thermal stress in the surface layer and interface between substrate and cladding layer are compressive stress, which is directly proportional to laser power and inversely proportional to scanning speed. It is easily to form crack initiation in the interface between substrate and cladding layer, for the amplitude of tension stress is larger in Z direction. As the tensile stress in X direction is much greater than that of Y direction, most of cracks are perpendicular to the scanning direction.The experimental results of Fe-Al composite coatings show that it is free of crack within coatings, and the porosity and inclusions are fewer. The microstructures of surface layer, middle of coating and zone near the interface are equiaxed crystal, columnar crystal and plane crystal. The Fe-Al composite coatings consist mainly of Fe, Al, Al₂O₃, and Fe₃Al. With the increase of laser power and scanning speed, the hardness and wear resistance of cladding layer got the peak value. The hardness of Fe-Al composite coatings is about 298HV, and the hardness and wear resistance are raised by one times and 50 percent compare to substrate. The optimal process parameters are: the laser power is 1400W and scanning speed is 400mm/min, which are consistent with the simulation results.As reinforcement element, silicon could significantly refine the microstructure of Fe-Al composite coatings and improve the hardness and wear resistance. The surface of Fe-Al-Si composite coatings is smooth, free of crack and porosity. With the increase of distance from interface, the microstructures are plane crystal, cystiform crystal and equiaxed crystal. The Fe-Al-Si composite coatings consist mainly of Fe, SiO₂ and Al₂Fe₃Si₄. The hardness of Fe-Al-Si composite coatings is up to 556HV. Compare to Fe-Al composite coatings, the hardness and wear resistance are both raised by one times; while compare to substrate, the hardness and wear resistance are raised by 3 times and 2.5 times. The optimal process parameters of Fe-Al-Si composite coatings obtained by orthogonal test are: the mass fraction of Fe, Al and Si is 8:1:1, the laser power is 1600W and scanning speed is 400mm/min.