Papers by Author: Jin Zhang

Abstract: In this paper, TiN coating was deposited onto the nitrided 32Cr2MoVA by multi arc ion plating and proceeded line contact fatigue experiment to investigate the influence of hard coatings on the contact failure properties of nitriding steel. The results of experiment show that pitting is primary type of contact fatigue failure for TiN coated 32Cr2MoV and the pits on the TiN coated surface are shallower and smaller than that of the nitrided 32Cr2MoV. After TiN coating produce crisping and desquamation under higher contact fatigue loads, the exposed matrix surface begin to bear the contact load. The superficial microstructure of TiN coated 32Cr2MoV was more fine, and content of nitrides were higher than that of the nitrided, which insured the distribution of hardness gradient of subsurface was more rational than that of nitrided 32Cr2MoV. The contact fatigue strength of TiN coated 32Cr2MoV is greater about 200MPa than that of the nitrided 32Cr2MoV.

Abstract: A protective zinc-aluminum spray coating and a post heat treatment was carried out onto AZ91D magnesium alloy. The effect of post heat treatment on the interfacial characteristics, corrosion behaviors, micro-hardness, and thermal shock resistance of the zinc-aluminum coating were evaluated in this paper. It was found that a dense inter-coating formed at the Zn/Mg substrate interface followed by the post heat treatment. The results of EDS analysis indicated that the diffusion took place among Mg, Al and Zn atoms. The Zn-Al deposited coating with heat treatment had much more corrosion resistant and higher resistant to thermal shock. It was harder than as-received AZ91D Mg alloy.

Abstract: Aluminum spray coating was applied onto AZ91D magnesium alloy. The effects of post heat treatment on the interfacial characteristics, especially the diffusion kinetics of magnesium and aluminum atoms across the interface were studied in this paper. It was observed that there was an obvious interface between the aluminum coating and the magnesium alloy substrate. It was found that post heat treatment could reduce the number of pores existed in the aluminum coating. The post heat treatment resulted in not only the change in the composition and microstructure of the aluminum coating, but also the improved metallurgical bonding between the coating and the substrate.

Abstract: In the present paper, nine kinds of alloys with different contents of zinc and zirconium were cast and the influence of zinc and zirconium individually and jointly on the microstructure of the ZK alloys were investigated. The results indicated that the shape and amount of the eutectic were closely related to the content of Zn. With the increase of Zn content, the eutectic was prone to have fish-bone-like shape. When the eutectic grew up to contact with each other, then network eutectic formed; Zr could intensively refine not only the grain size but also the eutectic, but when Zr>0.6%, compound containing Zr or pure Zr granules would appear. That the increase of the Zn must go with the increase of the Zr proved the combined influence of the two alloy elements.

Abstract: The microstructures of magnesium alloy AZ91D in as-cast, solid solution and aging conditions were studied by optical, scanning electron and transmission electronic microscopes. The relationship between microstructure and the microhardness was analyzed. It has been found that the microhardness in the matrix varied slightly with the increasing solution time, but increased quickly with the aging time. The difference of the microhardness between the matrix and the second phase in as-cast condition is larger than that in T6 aging condition, because the aluminum-zinc-magnesium (poor) phase existed in the as-cast condition.

Abstract: The current status of research and application in the AZ(Mg-Al-Zn), AS(Mg-Al-Si), AE(Mg-Al-RE), AX(Mg-Al-Ca), ACM or MRI（Mg-Al-Ca-RE）and AJ（Mg-Al-Sr）series elevated temperature magnesium alloys are reviewed, will special attention paid to the effects of alloying elements and the control of second phases. The existing problems on the development of elevated temperature magnesium alloys are discussed.

Abstract: The synergistic fluoropolymer self-lubrication coatings on magnesium alloys were studied. Magnesium alloy was firstly treated by electroless nickel plating. Then micropores of electroless nickel plating layer was enlarged. Then the fluoropolymer particles were infused into micropores, precise vacuum heat treatment ensured thorough infusion with fluoropolymer, finally the synergistic coating was formed. The hardness of the coating reached 600HV, the dynamic coefficient of friction of the coating was less than 0.15, and the low coefficient of friction could be kept during a long duration wear to realize the permanent dry lubrication. The corrosion resistance was also excellent to endure 5% neutral salt spray test for 500 hours. Also the structure and composition of the coating were observed and studied.