In this study, the effects of cerium (Ce) addition on the friction and wear properties of surface welding AZ91 magnesium alloys were evaluated by pin-on-disk dry sliding friction and wear tests at normal temperature. The results show that both the friction coefficient and wear rate of surfacing magnesium alloys decreased with the decrease in load and increase in sliding speed. The surfacing AZ91 alloy with 1.5% Ce had the lowest friction coefficient and wear rate. The alloy without Ce had the worst wear resistance, mainly because it contained a lot of irregularly shaped and coarse β-Mg17Al12 phases. During friction, the β phase readily caused stress concentration and thus formed cracks at the interface between β phase and α-Mg matrix. The addition of Ce reduced the size and amount of Mg17Al12, while generating Al4Ce phase with a higher thermal stability. The Al-Ce phase could hinder the grain-boundary sliding and migration and reduced the degree of plastic deformation of subsurface metal. Scanning electron microscopy observation showed that the surfacing AZ91 alloy with 1.5% Ce had a total of four types of wear mechanism: abrasion, oxidation, and severe plastic deformation were the primary mechanisms; delamination was the secondary mechanism.
Porous materials have excellent functions in filtration and purification, and gradient composite porous materials enrich the product types of porous materials in the same field. In the preparation of metal-ceramic gradient composite porous materials, the matching relationship between the pore morphology and pore size of the metal porous matrix and the coated powder particles will seriously affect the structure and performance of the ceramic membrane. This work mentions the different size range (60, 100, 200 and 400 mesh) of 316 L stainless steel powder particles as the raw materials which are at different sintering temperatures of 1170, 1200 and 1230 °C, the fabrication of porous 316 L stainless steel substrate which was made by hanging slurry preparation of precursor, at the same time using Ar protection at different sintering temperatures (650, 700, 750 and 800 °C) to the preparation of metal-ceramic composite gradient according to different matrix apertures of porous materials. The pore structure, microstructure and morphology characteristics of different samples both of matrix and functionally gradient composite were analyzed and characterized. On the basis of test of permeability of functionally gradient composite porous materials, this kind of composite gradient porous material can be excellent at part of permeability which matrix was made by 400 mesh 316 L stainless steel powder particles at sintering temperature of 1230 °C and then dealed with the process of hanging slurry to became the precursor which ceramic membrane was prepared at sintering temperature of 650 °C. Maximum aperture of the porous substrate filtration precision under the combination of ceramic membrane layer can be increased by 96.3%. By observing the change of pore morphology of porous matrix, this paper aims to make a research of influence of sintering temperature and powder particles size on permeability of the functionally gradient composite porous materials, and also provide a reference for improving the filtration accuracy of existing porous materials.
Dynamic and static aging precipitation of Mg 17 Al 12 phases in AZ80 magnesium alloy was studied by multidirectional forging (MDF) with decreasing temperatures from 410 to 300°C and subsequent aging process. The results show that the morphology of the b-Mg 17 Al 12 phases during forging process dynamically precipitates and aging process (statically precipitation) exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the b-Mg 17 Al 12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg 17 Al 12 phases but the grain is still coarse where there is no Mg 17 Al 12 phases. During the aging process, the morphology of newly formed b-Mg 17 Al 12 phases depends on the structural character of the forged sample. The newly precipitated b-Mg 17 Al 12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated b-Mg 17 Al 12 phases are fine granular and needle-like in the area with fine grain.
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