The temperature dependence of the viscosity of liquid Al-12wt.%Sn-4wt.%Si was studied with a hightemperature viscosity apparatus.Anomalous changes of viscosity of the melt were found at 1,103 K and 968 K in the cooling process,which indicates anomalous structural changes of the melt.It is calculated that the anomalous structural change is associated with an abrupt decrease of atomic clusters'size and activation energy in the melt.According to the temperature of the anomalous structural changes,melt heat treatment process(quenching from superheat to pouring temperature) was performed on Al-12wt.%Sn-4wt.%Si melt prior to pouring,aimed to keep the small atomic clusters from higher temperature to lower pouring temperature.The results suggest that relatively small atomic clusters at the pouring temperature in the melt could generate a deep under-cooling of nucleation in the subsequent solidification process,and refine the as-cast structure.After being quenched from superheating to pouring temperature,the relatively small atomic clusters,especially the Si-Si clusters in the melt will grow to equilibrium state(relatively big atomic clusters) with holding time,resulting in the prominent coarsening of the Si morphology in the as-cast structure.
Wang ZhimingGeng HaoranZhou GuorongGuo ZhongquanTeng Xinying
The influence of cooling rate and addition of La and Ce on the formation of nanoporous copper by chemical dealloying of Cu15Al85 alloy was studied.The components and microstructures of nanoporous copper were characterized by utilizing X-ray diffraction,field emission scanning electron microscopy and energy dispersive X-ray analysis.N2adsorption/desorption experiments were used to evaluate specific surface areas of samples.The results showed that,with the increase of cooling rate,phase composition of precursor alloy almost had no change,the ligament size of nanoporous copper had a decrease trend,and specific surface area increased gradually.And it was found that the specific surface area of the nanoporous copper obtained by Cu15Al85 alloy containing La and Ce was 63.258 m2/g,which was more than 11.739 m2/g compared with the nanoporous copper dealloying by Cu15Al85 alloy without La and Ce under the same conditions.
