Shae K. Kim

Effect of CaO composition on oxidation and burning behaviors of AM50 Mg alloy

Oxidation and burning behaviors were studied for CaO added AM50 Mg composites which were manufactured by conventional melting and casting processes without SF6 protective gas. CaO added AM50 Mg composites show the stable oxidation resistance, while AM50 Mg alloys show the poor oxidation resistance. The effects of CaO addition on the burning resistance under ambient, nitrogen and dry air atmospheres were examined for CaO added AM50 Mg composites. With increasing CaO addition, the burning temperature increases under ambient, nitrogen and dry air atmospheres. The burning temperatures of small test specimen under all conditions greatly increase even by 0.3% CaO (mass fraction) addition into AM50 Mg alloys.

Microstructural evolution and semisolid forming of SiC particulate reinforced AZ91HP magnesium composites

Abstract The aim of this paper is to report the experimental results concerning the microstructural evolution and formability of semisolid forming SiC particulate reinforced AZ91HP Mg composites. The composite materials were produced in the form of cylindrical billets by a rotating cylinder method. The microstructural evolution was characterised by conventional parameters (liquid fraction, average size of globules, and number of globules per unit area) as functions of temperature and isothermal holding time in the semisolid state. In addition, special attention was paid to the shapes of the globules and the liquid droplets entrained within the globules and to the variation of hardness with regard to microstructural evolution. Finally, the formability of the composites was evaluated through thixocasting trials, and then correlated with the effective liquid fraction of the composites.

Rotating cylinder manufacturing method and investment casting of SiCp/AZ91HP magnesium composites

Abstract This paper describes the rotating cylinder method for manufacturing, and investment casting for forming, composite slurry. Microstructural features, such as SiC particle distribution and grain refinement of the as cast composites, were investigated. Also the effect of SiC particle fraction and size, and process parameters on the microstructure and the mechanical properties are discussed. Attempts were made to evaluate the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZrO3, and silica bonded Al2O3 and zircon flour. Finally, the tensile properties, hardness, and wear resistance of the as cast composites were evaluated and the results are compared with those of the as cast alloy.

Microstructural Evolution of A206 Al Alloy by In-Ladle DTC Rheocasting

This study is mainly concerned about the possibility to achieve semisolid slurry during partial solidification only through thermal and time control, that is, by In-Ladle direct thermal control (DTC) rheocasting for A206 Al alloy. This is based on the fact that there is slurry and mush transition in molten metal, which is controlled by the shape of solid and the relative energy. Thermal modeling of heat behavior with respect to ladle material and ladle design was investigated by 2-dimensional finite volume method (FVM). Based on the optimum conditions obtained by thermal modeling, microstructural evolution of A206 Al alloy by In-Ladle DTC rheocasting was carried out. Also, fluidity was investigated by actual In-Ladle DTC rheocasting for optimizing conditions of A206 Al alloy.

Optimisation of process variables for manufacturing aluminium foam materials using aluminium scrap

Abstract An attempt has been made to develop a high profit recycling process for aluminium scraps, by which high performance aluminium foam materials could be produced directly from scrap. This is based on the fact that oxides on the surface of aluminium scrap can act as a viscosity thickener, the basic necessity for molten processes of aluminium foams. The main emphasis of this study is on optimisation of the process variables for manufacturing aluminium foam materials by direct foaming of remelted aluminium scrap.

Rheological behaviour and fluidity of SiCp+AZ91HP magnesium composites

Abstract Rotating cylinder viscosity and spiral fluidity experiments were carried out to investigate the effects of SiC particle fraction and size and casting temperature on the viscosity and the fluidity of Mg–8.2Al–0.7Zn (wt-%)alloy containing up to 10 vol.-%SiC particles. The rotating cylinder viscosity (process based viscosity) was deduced from the data measured by a power measurement system during the actual composite manufacturing by the rotating cylinder method, and the fluidity was measured using a specially designed spiral fluidity mould. The spiral fluidity, which is the reciprocal of viscosity, decreased with increasing SiC particle fraction (for a given size) and with decreasing SiC particle size (for a given volume fraction). Although the decrease in the fluidity of the composite slurry was observed due to the expected increase in the viscosity by the presence of SiC particles, the results showed that the fluidity of the composite slurry with 10 vol.-% 50 µm SiC particles was adequate to make a variety of castings at 680°C.

Thixoextrusion for 7075 Al Wrought Alloy Tube

The aim of this study was to improve extrudability limit, eliminate welding line and obtain optimum thixoextrusion conditions for manufacturing tubes of 7075 Al wrought alloy. By thixoextrusion, it was possible to improve deformability, control isotropy with extrusion direction, eliminate welding line (seamless) and save cost due to low energy consumption compared with conventional extrusion processes. The welded part was not observed at the welding line area. The grains of thixoextruded tube were homogeneously distributed and equiaxed grains were observed. Therefore, thixoextrusion is the most effective variable for the control of the magnitude of the welding line.

Effect of Aluminum on the Corrosion Characteristics of Mg-4Ni-xAl Alloys

Abstract Corrosion properties of Mg-4Ni-xAl alloys were investigated using electrochemical techniques, pH measurement, hydrogen evolution test in acid-chloride solution (pH 5.4, 200 ppm Cl−), and s...

Effect of CaO Addition on High Temperature Tensile Properties of Mg Casting Alloys

The microstructure, hardness and tensile properties of Mg-3Al, Mg-3Al-1.2Ca(AX31), Mg-3Al-1.2CaO(AO31), Mg-9Al, Mg-9Al-1.2Ca(AX91) and Mg-9Al-1.2CaO(AO91) alloys were investigated to identify the effect of CaO addition compared with Ca addition. The results show that the alloy element CaO has a good effect on high temperature tensile properties and CaO added alloys have superior high temperature performance compared with Ca added alloys. Addition of CaO results in the precipitation of Al2Ca phase (C15 phase) on the grain boundaries. This phase precipitated by the reduction of CaO leads to the refinement of a microstructure and improvement of tensile properties at elevated temperature similar to the Ca added Mg alloys. When added into molten Mg Ca makes solid solution in the Mg matrix up to 0.8wt %. But in case of CaO addition the thermally stable compound is precipitated directly without making solid solution with Mg matrix. Therefore, the high temperature tensile properties of CaO added Mg casting alloys are better than Ca added one at the same adding contents (1.2wt.%).

Microstructural Control of 7075 Al Wrought Alloys through Thixoextrusion Route

Thixoextrusion, one of the thixoforming processes, has advantages of high productivity, reduction of the extrusion pressure, extension of the die life, and cost saving owing to its low energy consumption compared with the conventional extrusion processes. Especially, thixoextrusion process is expected to be very effective for hard-to-form materials with high strength. The present study focuses on 7075 Al wrought alloy to investigate the potential industrial applications of the thixoextrusion process. The microstructural evolution of 7075 Al wrought alloy for thixoextrusion was investigated with respect to isothermal holding temperature and time in the partially remelted semisolid state. The results showed that the liquid fraction increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time up to 5min. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding temperature and time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min holding time is considered very useful for thixoextrusion in terms of process control.