The formation behavior and corrosion characteristics of anodic oxide films on pure magnesium and on Mg-Al alloys were investigated, focusing on the effects of anodization potential, aluminum content, temperature, and NaOH concentration. Pure magnesium and Mg-Al alloys were anodized for 600 s at 3, 10, 40, and 80 V in NaOH solutions. It was found that the anodic film formed at 3 V had the best corrosion resistance, regardless of temperature, NaOH concentration, or aluminum content. An especially high current density was observed at applied potentials of 3-7 V on anodization in alkaline NaOH solutions. XRD analysis detected Mg(OH) 2 and MgO peaks in the films on the anodized specimens. The relative intensity of the Mg(OH) 2 XRD peaks decreased with increasing applied potential, while those of MgO increased. Mg(OH) 2 was generated by an active dissolution reaction with high current density at the specimen surface. Generation of Mg(OH) 2 increased with increasing temperature, while that of MgO increased with NaOH concentration. Moreover, the current density after anodization for 600 s at a constant potential decreased with increasing aluminum content in Mg-Al alloys.
Chemical conversion treatment of Mg-Al alloy (AZ91) using colloidal silica as an alternative to chromate conversion was investigated as a function of solution pH, temperature, solution conditions, and treatment time. The solution used for the colloidal silica coating consisted of colloidal silica, titanium sulfate, and cobalt ions to maintain good anti-corrosion and adhesion properties. Adding CoSO 4 to the colloidal silica solution enhanced the adhesion force between the silica film and magnesium substrate. The optimum conditions for the chemical conversion treatment solution were pH 2, 90-sec treatment, and 25 o C.
The deflection of a die in high-pressure die-casting (HPDC) strongly influences the quality of HPDC parts. The dimensional accuracy is the most important point. This research developed a method to estimate the die deflection in HPDC using FFM computer simulation. First, the effect of the distortion of the die-casting machine on the deflection of the die-insert was evaluated. It is possible to partly evaluate the deflection of the di-insert without installation in the die-casting machine. However, an actual distortion measurement of the die-insert demonstrated that the calculation including the die-casting machine can precisely evaluate the die-insert distortion. Second, the thermal distortion of the die was taken into consideration. A FDM flow and solidification simulation calculated the temperature distribution of the die-insert. The calculated distribution was confirmed to correspond to the actually measured temperature distribution. Finally, the deflection of the die-insert caused by the die-clamping as well by the thermal distortion was simulated. It was found that the calculated deflection well coincides with the actually measured strain value. From these steps, it was clarified that the computer simulation on the HPDC system including the structural machine can precisely evaluate the deflection of the die-insert.
A computer simulation method to predict the thermal distortion value of a high-pressure die cast part was investigated. The evaluated product was a flat-shape JIS ADC12 part. The actual distortion value of the part was measured by an optical 3D digitizer and it was compared with the predicted distortion value. In this method, the initial temperature distribution of the part was determined by casting simulation. The thermal distortion value during cooling was calculated by FEM analysis. The stress-strain relation was approximated by the elastic-perfectly plastic material model including the temperature dependence of the yield strength. It was found that the heat-transfer coefficient between the die and the injected molten metal is a critical factor to implement an accurate FEM simulation in the casting simulation. The heat-transfer coefficient value was accessed and confirmed using the temperature distribution measured by a thermo camera. The distortion values of the actual part optically measured as a function of the curing time well coincided with the simulated value. It was concluded that the method can predict the distortion within a practically accepted preciseness.
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