Moldflow Simulation and Characterization of Pure Copper Fabricated via Metal Injection Molding.

Metal injection molding (MIM) is a representative near-net-shape manufacturing process that fabricates advanced geometrical components for automobile and device industries. As the mechanical performance of an MIM product is affected by green-part characteristics, this work investigated the green part of pure copper processed with MIM using the injection temperature of ~180 °C and injection pressure of ~5 MPa. A computational analysis based on the Moldflow program was proposed to simulate the effectivity of the process by evaluating the confidence of fill, quality prediction, and pressure drop of three distinctive regions in the green part. The results showed that the ring and edge regions of the green parts showed localized behavior, which was related to processing parameters including the position of the gate. A microstructural observation using scanning electron microscopy and a 3D X-ray revealed that both the surface and body matrix consisted of pores with some agglomeration of micro-pores on the edges and ring part, while any critical defects, such as a crack, were not found. A microhardness analysis showed that the three regions exhibited a reasonable uniformity with a slight difference in one specific part mainly due to the localized pore agglomeration. The simulation results showed a good agreement with the microstructures and microhardness data. Thus, the present results are useful for providing guidelines for the sound condition of MIM-treated pure copper with a complex shape.

Electron-Donor and -Acceptor Agents Responsible for Surface Modification Optimizing Electrochemical Performance.

The electrochemical roles of electron-donor and -acceptor agents in surface reforming of magnesium alloy were investigated via plasma electrolysis. The surface modification was performed in an aluminate-based electrolyte, having urea and hydrazine with inherent molecular structures, which might act as electron acceptor and donor during plasma-assisted electrochemical reaction. The presence of hydrazine working as donor would promote the formation of magnesium aluminates in the oxide layer, resulting in superior compactness of the oxide layer to that when urea was used as the working as acceptor since the precipitation of MgCO3 was favored in the electrolyte with urea. The thickness of the oxide layer formed by a combination of urea and hydrazine was higher than urea, while the porosity was higher than hydrazine. The electrochemical performance was enhanced in the order of hydrazine, urea and hydrazine combined, and urea, which was discussed on the basis of impedance interpretation.

Toward a nearly defect-free coating via high-energy plasma sparks.

A nearly defect-free metal-oxide-based coating structure was made on Al-Mg-Si alloy by plasma electrolytic oxidation at high current density accompanying high-energy plasma sparks. The present coatings were performed at two different current densities of 50 and 125 mA/cm2 in the alkaline-phosphate-based electrolytes with different concentrations of sodium hexafluoroaluminate (Na3AlF6). The addition of (Na3AlF6) to the electrolyte used in this study would result in a decrease in the size of the micropore, and a reasonably defect-free coating structure was achieved in the sample treated at high current density of 125 mA/cm2. This was attributed mainly to the hydrolysis of AlF63- triggered by intense plasma sparks, which resulted in a uniform distribution of fluorine throughout the coating. Accordingly, the corrosion performance of the coating formed in the electrolyte containing 1.5 g/L Na3AlF6 at 125 mA/cm2 was improved significantly as confirmed by electrochemical impedance analysis. In addition, the formation mechanism of the nearly defect-free coating in the presence of Na3AlF6 was discussed.