Papers by Author: Yong Zhi Zou

Abstract: The structure and properties of A357 aluminum alloy with different second dendrite arm spacing (SDAS) in different situations of overheating were investigated. The results indicate that serious overheating characteristic structure takes on compound melting ball, crystal separating phase and overheating triangle section; The overheating level of A357 alloy raises with solution temperature increasing; The mechanical properties decrease with the overheating level increasing; The overheating temperature of casting increases as the SDAS decreases, the regression equations of the correlation between SDAS and overheating temperature is as follows: T = 575.46-0.213SDAS; Optimum solution temperature could be selected for A357 alloy with different SDAS depending on supercritical solution region proposed in this paper.

Abstract: The scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to characterize samples prepared from the surface scum of melt, the middle flake residues on the furnace wall and the “bottom bulk” after the A357 alloy pouring. The morphology and impurities composition of these features were investigated. Some of particles and regions in samples during the analyses were also studied in detail. The results of analyses show that the surface scum of melt include Al2O3, MgO or MgAl2O4; the impurities of the middle flake residues is comprised of Al2O3, MgO or MgAl2O4, as well as SiO2 particle, Al9Fe2Si2 compound and dimple like C-rich areas; the bottom bulk contains C-rich impurities such as Al4C3 or some of unknown phase or elemental carbon.

Abstract: Aluminum alloy A357 can be heat treated in order to obtain optimum mechanical properties. Moreover, SDAS (Second dendrite arm spacing) is an important structure feature in cast aluminum alloys. The effects of SDAS on the homogenization of Al-Si-Mg alloy are investigated through measurement of SDAS and hardness analysis. The results show that the homogenization time increases as the value of SDAS increases and the homogenization temperature decreases in the homogenization process. The homogenization kinetics equation is: . In addition, the hardness after homogenization treatment at 540°C for 6 hours is advanced with the reduction of SDAS.

Abstract: This present work investigate the hydrogen content in Al-12Si alloy at different holding temperatures of 993K, 1023K, and 1053K and under different ambient relative humidity 30%RH, 50%RH, 80%RH. The relationship of the hydrogen content with atmosphere relative humidity and the reaction time was investigated. A HYSCAN II analyzer was used to evaluate the hydrogen content in aluminum melts. The experimental results show that the hydrogen content increased with the holding temperature and the relative humidity. At the temperature 1053K, the hydrogen content has an inverse change. The hydrogen content is more depend on the liquid structure than physical mass transfer and chemical reaction because of the sudden change in liquid microstructure. A group of kinetic regression equations of the hydrogen absorption in Al-12Si melts was obtained.

Abstract: Microporosity in cast aluminum alloys formed during solidification of castings can be due to the evolution of dissolved hydrogen gas from the liquid metal, the inability of liquid metal to feed through interdendritic channels, or a combination of both. The secondary dendrite arm spacing (SDAS) of the casting may affect either the evolution of hydrogen gas or the ability of feeding. In this investigation, a method based on the Nearest-Neighbor-Distance (NND for short) cluster analysis of image analysis data was used for distinguishing the gas and shrinkage pores in A357 alloy, in order to study the effects of SDAS on the microporosity formation. It shows that the shrinkage pores are prone to form in the specimens with small SDAS. The discrete, isolated gas microporosity is prone to form in the specimens with large SDAS.