EFFECTS OF Ce ON CORROSION RESISTANCE OF AZ91D MAGNESIUM ALLOY

As-cast and corrosive microstructures of AZ91D alloy containing various Ce contents were observed by optical microscope (OM). The phase compositions of the alloys before and after the corrosion were analyzed by X-ray diffraction (XRD). Meanwhile, the corrosion resistance of the alloys was tested by weight loss and potentiodynamic polarization curve methods respectively. The results show that rod-like Al4Ce phase is formed in AZ91D alloy containing certain Ce content and as-cast microstructures are refined. AZ91D-0.7%Ce alloy has good grain refinement effect. The addition of Ce can reduce the corrosion rate and corrosion current density of AZ91D alloy and those of AZ91D-0.1%Ce alloy reach the minimum, which are 0.35mg/(cm2·d) and 2.761μA/cm2 with 75% and 86% reduction, respectively. The increasing volume fraction and reticular degree of β phase can improve the corrosion resistance of the alloys.

Design and preparation of Al-Fe-Ce ternary aluminum alloys with high thermal conductivity

Ce element was introduced to modify Al−2%Fe(mass fraction)binary alloy.The microstructures,crystallization behavior,electrical/thermal conductivities and mechanical properties of these alloys were systematically investigated.The results indicated that the appropriate Ce addition decreased the recalescence temperature and growth temperature of Al−Fe eutectic structure,improved the morphology and distribution of Fe-containing phase,and simultaneously increased the conductivity and mechanical properties.The annealed treatment improved the thermal conductivity of these alloys due to the decreasing concentration of point defects.Rolling process further broke up the coarser Fe-containing phases into finer particles and made the secondary phases uniformly distributed in theα(Al)matrix.After subsequent annealing treatment and rolling deformation,the thermal conductivity,ultimate tensile strength and hardness of the Al−2%Fe−0.3%Ce(mass fraction)alloy reached 226 W/(m·K),(182±1.4)MPa and HBW(49.5±1.7),respectively.

Evolution mechanism of active sites for selective catalytic reduction of NO_(x) with NH_(3) over Fe-ZSM-5 catalysts doped by Ce/Cu

Fe-ZSM-5 catalysts modified by Cu and Ce by aqueous solution ion-exchange and incipient wetness impregnation methods were tested in the selective catalytic reduction of NO_(x) with NH_(3).A variety of characterization techniques(NH_(3)-SCO,BET,XRD,XPS,UV-Vis,NH_(3)-TPD,H_(2)-TPR)were used to explore the changes of the active sites,acid sites and pore structure of the catalyst.It was found that the dispersion of active Cu species and Fe species had great influences on the catalytic activity in the whole catalytic process.The Cu doping into the Fe-ZSM-5 catalyst produced new active species,isolated Cu ions and CuO particles,resulting in the improved low-temperature catalytic activity.However,the NH_(3) oxidation was enhanced,and part of the Fe^(3+)active sites and more Brønsted acidic sites in the catalyst were occupied by Cu species,which causes the decrease of the high-temperature activity.The recovery of hightemperature activity could be attributed to the recovery of active Cu species and Fe species promoted by Ce and the promotion of active species dispersion.The results provide theoretical support for adjusting the active window of Febased SCR catalyst by multi-metal doping.

Improving thermal conductivity of Mg-Si-Zn-Cu alloy through minimizing electron scattering at phase interface

The primary cause of the decrease in thermal conductivity of conventional thermal conductive magnesium alloys is electron scattering brought on by solute atoms.However,the impact of phase interface on thermal conductivity of magnesium alloys is usually disregarded.This study has developed a Mg-Si-Zn-Cu alloy with high thermal conductivity that is distinguished by having a very low solute atom content and a significant number of phase interfaces.The thermal conductivity of the Mg^(-1).38Si-0.5Zn-0.5Cu alloy raises from its untreated value of 133.2 W/(m·K)to 142.2 W/(m·K),which is 91%of the thermal conductivity of pure Mg.This is accomplished by subjecting the alloy to both 0.8wt%Ce modification and T6 heat treatment.The morphology of eutectic Mg_(2)Si phase is changed by Ce modification and heat treatment,and as a result,the scattering of electrons at the Mg_(2)Si/Mg interface is reduced,resulting in increase of the alloy’s thermal conductivity.

Effects of cerium and phosphorus on microstructures and properties of hypereutectic Al-21%Si alloy

The influences of P and rare earth （RE） complex modifier on the microstructure and mechanical properties of hypereutectic Al-21%Si alloy were studied. The ingots were made by metal mold casting and the proportion of Ce＋P ingredient was different. The result showed that the size of grains could be refined obviously by the Ce＋P modifier and the effect of phosphorus was more intensive The primary silicon crystal was refined, while the needle-like eutectic silicon was turned fibrous or short. The alloy mechanical prop- erties had the best performance when 0.08% P and 0.6% Ce were added. The modification of primary silicon grains mainly depended on the heterogeneous nucleation mechanism, and the metamorphic mechanism of eutectic silicon was explained by adsorbing-twirming theory. The strengthening mechanism of experimental alloy was also discussed. The σb, 20 ℃ increases from 236.2 to 287.6 MPa and σb, 300 ℃ increases from 142.5 to 210 MPa.