The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain sizesmaller than 10μm can be obtained by the extrusion processing. Vickers hardness measurements were also ...The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain sizesmaller than 10μm can be obtained by the extrusion processing. Vickers hardness measurements were also carriedout to evaluate the effect of these processes on the room temperature mechanical properties. The experimentalresults of high temperature tensile tests revealed that the stress was inversely proportional to the square of the grainsize and that the activation energy for superplastic flow was higher than that for grain boundary diffusion.展开更多
The bonding and electronic structures of oxy-gen molecules adsorbed on Al (001) are theoretically investi-gated from first-principles using the density functional the-ory within the generalization gradient approximati...The bonding and electronic structures of oxy-gen molecules adsorbed on Al (001) are theoretically investi-gated from first-principles using the density functional the-ory within the generalization gradient approximation (GGA) and a supercell approach. The surface is described by means of a 2×2 cell with a thickness of fourteen layers, which con-sist of 9 layers of Al atoms and 5 layers of vacuum. Oxygen molecules are situated on Al surface. The calculated results indicate that oxygen molecules with their axes parallel to the Al surface are the energetically easiest to be adsorbed on Al (001), while those vertical to the Al surface are the most dif-ficult. There are two different processes for the adsorption of oxygen molecules on Al (001), which are O2?(O2)2-?2O-?2O2- and O2?(O2)- ?O2-+O, and their occurrences are strongly dependent on the initial morpholo-gies.展开更多
基金The autlors gratefully acknowledge the financial support from the National Commnittee for High Technology ResearchDevelopment of China under the project No.2002AA331120.
文摘The effect of extrusion on grain refinement has been studied in the AZ91 cast ingots. It is found that grain sizesmaller than 10μm can be obtained by the extrusion processing. Vickers hardness measurements were also carriedout to evaluate the effect of these processes on the room temperature mechanical properties. The experimentalresults of high temperature tensile tests revealed that the stress was inversely proportional to the square of the grainsize and that the activation energy for superplastic flow was higher than that for grain boundary diffusion.
文摘The bonding and electronic structures of oxy-gen molecules adsorbed on Al (001) are theoretically investi-gated from first-principles using the density functional the-ory within the generalization gradient approximation (GGA) and a supercell approach. The surface is described by means of a 2×2 cell with a thickness of fourteen layers, which con-sist of 9 layers of Al atoms and 5 layers of vacuum. Oxygen molecules are situated on Al surface. The calculated results indicate that oxygen molecules with their axes parallel to the Al surface are the energetically easiest to be adsorbed on Al (001), while those vertical to the Al surface are the most dif-ficult. There are two different processes for the adsorption of oxygen molecules on Al (001), which are O2?(O2)2-?2O-?2O2- and O2?(O2)- ?O2-+O, and their occurrences are strongly dependent on the initial morpholo-gies.
