Plates (M1) of tungsten and molybdenum with 0.3 and 0.2mm thick have been bonded to substrates (M2) of iron and nickel, respectively, under HIP at 800-1200°C, 10-200MPa for 30min. Because the HIP method results in complete contact at the M1-M2 interface, no pores were observed. A diffusion layer was observed between M1, and M2, and its thickness, including the reaction layer, increased with an increase in temperature. Thickness decreased with an increase in HIP pressure, suggesting that the pressure suppresses the diffusion of the atoms of M1 and M2. Despite the large difference in the thermal expansion coefficients of M1 and M2, the bonding resisted over 40 repetitions of 900°C thermal shock. It is suggested that the diffusion layer act to reduce thermal stress. Further, since the interface did not give even under bending stress, it is suggested the HIP pressure plays an important role in increasing the strength of the bond between M1 and M2.
The change in the degree of surface degreasing with electrolytic degreasing time was investigated by an electrochemical method. Interfacial impedance was measured during electrolytic degreasing with cathode current, and/or after electrolytic degreasing for a certain period. The cathode current was set at 5mA to allow slow monitoring of the degreasing process. The analysis was conducted in terms of values of θ, which is an index of the surface reaction uniformity, double layer capacitance, Cdl, and the reaction resistance, Rp. During electrolytic degreasing, the value of θ decreased and that of Cdl increased with decreasing time. The values of θ and Cdl were constant after electrolytic degreasing was completed. After electrolytic degreasing for a certain period, θ and Rp decreased and Cdl increased. It is suggested that the degree of electrolytic degreasing can be determined by monitoring impedance.
Aluminum alloy die castings and plates were anodized by applying direct current or a constant pulse voltage in a sulfuric acid solution. In DC anodization, castings containing large amounts of silicon and copper, there was a tendency for electrolytic voltage to rise and for the thickness of oxide coatings to decrease. Electrochemical parameters-ionic current density, zenar leading edge angle and zenar time were measured by analyzing the pulse current waveform. The ionic current density and zenar time for 99.99% aluminum were taken as the reference standard. Ionic current densities were lower for Al-Si and Al-Cu based alloys and higher values for Al-Mg based alloys, while zenar times were longer for Al-Si and Al-Cu based alloys, and shorter for Al-Mg based alloys. The pulse current waveforms for AC 4C, ADC 1 and DM 2 die castings were characteristic of porous film formation. ADC 10 and ADC 12 castings, on the other hand showed a borderline type between barrier film formation and porous film formation, since ionic current was relatively high. This seemed to be caused by imperfect barrier layer formation, based on the relatively high ionic resistance of silicon, trapping of electrons by cuprous oxide and the anodic dissolution of CuAl2.
The effects of organic food additives on pitting corrosion of aluminum alloys were studied in a neutral solution of sodium chloride. The advance of corrosion was estimated by time variation of the rest potential, anodic and cathodic polarization curves and polarization resistance. Pit depth was evaluated with an optical microscope and photoacoustic spectroscopy (PAS) was newly applied to evaluate the spatial distribution of corrosion pits. Results obtained were as follows. 1) Organic substances that showed an inhibiting effect, decreasing the maximum pit depth, were: for 3003 alloy DL-thioctic acid, caffein anhydride and L-tryptophan; for 5052 alloy casein; and for 6063 alloy pyridoxine hydrochloride and hydantoin. 2) In the presence of an organic substance as pitting corrosion inhibitor, obtained corrosion potential at pH7 shifted to the noble side, and these results support the evaluated results for the maximum pit depth. In an acid solution of pH3, obtained corrosion current decreased in the presence of the organic substance. These results suggests the possibility of an inhibitive effect inside the pits as well as outside the pits.