A Study On The Laser Cladding Of Nodular Cast Iron QT600-3

Laser cladding, which can bring excellent surfacial structure and properties of the parts, is a new surface modification technology,. It can be used to prepare high-performance alloy-steel surface which has super properties and high bonding strength with the base metal based on the simple steel. Especially, the technology plays a critical role in repairing the local parts which invalidated easily due to concentrated wear.Solid-state laser was adopted to prepare iron-based and nickel-based alloy powder coating on the surface of nodular cast iron QT600-3. Optical microscope, scanning electronic microscope (SEM), X-ray diffraction (XRD), transmission electronic microscope (TEM) and microhardness testing machine were utilized to analyze the microstructure, distribution of alloying agent, metallic phase structure and cross-sectional hardness distribution of the coating respectively. The results showed that:laser power, scanning speed, powder conveyer rotation speed and spot diameter have large effects on the shape and quality of the coating. The width W and height H of the cladding layer wereincreased with the increase of the laser power, but the hardness decreasesd. The higher the scanning speed was the superior the hardness of the cladding layer was. Similarly, with the higher scanning speed, the values of the width and height of the cladding layer were improved. However, the values of the width and height of the cladding layer were decreased with the powder conveyer rotation increasing. In addition, the effect is undetectable if the spot diameter value is in the effective range. the optimum processing parameter of iron-based alloy powder coating was:laser power P=800 W, scanning speed V=6.67 mm/s, spot diameter D=2 mm, powder conveyer rotation speed (powder feeding speed) R=300 rpm; that of nickel-based alloy powder coating was:laser power P=900 W, scanning speed V=10 mm/s, spot diameter D=2.5 mm, powder conveyer rotataion speed R=420 rpm. The microstructure of laser clad coating consisted of cystiform crystal and dendrite was homogeneous and free of pore. The elements Fe and Cr in coating and substrate near the interface diffuse from one side to the other, so that metallurgical bonding is formed between the coating and the substrate. The hardness of the coating is improved up to 2.6 times of the substrate because of the hard spots dispersing in the coating. In an ideal range of processing parameters, fine coating can be obtained in nickel-based alloy powder laser cladding.Besides, in this study the reasons for the formation of cracks, porosities, inclusions, segregation and fringe concavity in laser cladding layer were investigated, and solutions were addressed to avoid these defects, which can also provide technic support of laser cladding in the application of repairing auto mould.