Liyuan Niu

A black phosphate coating for C1008 steel

This paper describes an effective metal finishing technology for obtaining black phosphate coatings on steel. The black conversion coating obtained on steel (C1008, AISI) and cast iron (No.35, ASTM) was dense and uniform with a thickness up to 18 μm. The coating shows better corrosion resistance; lubricating ability and higher efficiency of light-absorption than the traditional phosphate coatings. The black phosphate-forming mechanism was investigated. It is shown that sodium molybdate added to the black phosphate treatment bath can refine the microstructure. Corrosion tests showed that the corrosion rate was lower than that of traditional phosphating. The black phosphate coating, when employed as the pretreatment layer before laser heat-treatment, can remarkably improve the efficiency of light-absorption during laser heat-treatment. This phosphate technology had been employed successfully on the production line in the automobile industry.

Influence of sodium metanitrobenzene sulphonate on structures and surface morphologies of phosphate coating on AZ91D

The gray phosphate coating was formed on AZ91D magnesium alloy from the zinc phosphating bath containing sodium metanitrobenzene sulphonate in about 4 min. The structure, surface morphologies and phase compositions of the phosphate coatings were observed and analyzed by using SEM, XRD and EDS. It is shown that the phosphate coating becomes denser and has less micro holes with increasing the concentration of sodium metanitrobenzene sulphonate in the bath in the range of 2.0 to 6.0 g/L. The addition of sodium metanitrobenzene sulphonate greatly increases the micro cathode sites for the formation of the phosphate coating and decreases the porosity of the coating.

Microstructure modifications and associated corrosion improvements in GH4169 superalloy treated by high current pulsed electron beam

The surface of the nickel-based superalloy GH4169 was subjected to high-current pulsed electron beam (HCPEB) treatment. The microstructural morphologies of the material were analysed by means of optical microscope (OP), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results reveal that the irradiated surface was remelted and many craters were formed. The density of craters decreased with the increment of HCPEB pulses. After 20-pulsed HCPEB irradiation, nanostructures were formed in themelted region of the surface. Furthermore, slipping bands and high density of dislocations were also formed due to the severe plastic deformation. The selective purification effect, homogenized composition, nanostructures, and dislocation slips introduced by HCPEB irradiation bring a significant improvement of corrosion resistance of GH4169 superalloy.