Galvanic corrosion at the joint of AZX611 magnesium (anode) and A6N01 aluminum (cathode) in 1 mass% NaCl solution with different cathode / anode area ratios was evaluated. The galvanic potential was different depending on the area ratio. The anode galvanic current density increased with increasing the area ratio. Anode and cathode weight loss corrosion rates, and the average of anode current densities, were linearly related to the logarithm of the area ratio with different slopes. Scanning vibration electrode technology (SVET) has exhibited the presence of anodic current spots that increased with the area ratio. Surface profile of the galvanic joint was in good agreement with the SVET results. The obtained effect of cathode / anode area ratio was analyzed by the mixed potential theory. Finally, the compatibility of magnesium / aluminum joint was compared with other dissimilar metal joints.

In this study, galvanic corrosion of an Al-Mg alloy A5052 and carbon steel SS400 couple in aqueous NaCl solution was investigated. Galvanic corrosion experiments were performed for 259.2 ks in aqueous NaCl solutions at various NaCl concentrations ranging from 5 mol/m³ to 500 mol/m³. Galvanic current and corrosion potential of the couplewere measured during immersion in the solutions. Corrosion potentials measured during the immersion in various concentrations of NaCl were almost constant for 7.2 ks and shifted in the less noble direction with increasing NaCl concentration. Galvanic currents between A5052 and SS400 showed positive values during the immersion in the solutions, indicating that A5052 side was basically an anode. These results indicated that galvanic corrosion between A5052 and SS400 in the early stage of immersion progressed under a diffusion-limiting condition for the reduction of dissolved oxygen on the SS400. However, galvanic corrosion behavior changed with immersion time in NaCl solutions of 5 and 50 mol/m³ ; the change in the galvanic corrosion behavior was attributed to the change in the anodic polarization behavior both on A5052 and SS400. The galvanic corrosion behavior of the A5052/SS400 couple in NaCl solutions were explained in detail.

Galvanic corrosion behavior of Al-Mg alloy A5052/carbon steel SS400 couples with different gaps was investigated in NaCl solutions at various concentrations. The corrosion morphology of the couples differed from each other depending on the gap and NaCl concentration. Steel corrosion was observed as NaCl concentration and/or the gap decreased. When the gap was 10 mm, no corrosion occurred on the SS400 side in all the test solutions, suggesting that anodic dissolution reaction was dominant on the AA5052 side. However, as the gap was decreased, the corrosion of the steel became obvious in the solutions at lower concentrations, although the A5052 also showed localized corrosion. These results indicated that anodic dissolution reaction was generated both on the A5052 and the SS400 under the smaller gap conditions with decreasing the NaCl concentrations. In this study, the effects of gap on the galvanic corrosion behavior were also discussed based on the results of the change in the solution chemistry in addition to galvanic current and potential of the A5052 and SS400 couples.

We investigated the galvanic corrosion behavior of aluminum alloy in contact with carbon steel during accelerated corrosion testing by evaluating the galvanic current and corrosion morphology of the coupled specimen. Electrochemical polarization curve was acquired before and after accelerated corrosion testing, with galvanic current only detected for aluminum dissolution. Aluminum next to the carbon steel was more severely corroded than remote aluminum. Corrosion was also observed in the carbon steel, although its dissolution current was not detected. Galvanic corrosion behavior was found to be dependent on the duration of exposure to water and the chemical composition of the aluminum alloy. The galvanic corrosion of aluminum was not only affected by the connected metal and the environment to which it was exposed, but also by the distance from the connected metal, and was dependent on the ion concentration of the connected metal.

To predict hot tearing during DC (direct chill) casting by thermal stress analysis, cooling rate dependence of viscous properties in semi-solid state are indispensable. However, those at cooling rates of DC casting had not been obtained in the past. In this study, a tensile test device with high frequency induction heating that can control the cooling rate was developed. By using this device, the viscous properties were obtained on Al-5mass%Mg alloy at 1 K/s and 5 K/s. To determine those, two methods were employed. The first method was to determine those from relationships between the maximum true stress, σ_max and the true strain rate, έ_max. The method suggested by Matsushita was employed as the second method. It was found that the viscous properties obtained by each methods were different at 1 K/s. This should be because the true strain rate was increased due to the formation of micro-damage inside the test piece at σ_max. The viscous properties of those that did not experience micro-damage were independent of the cooling rate. This should be because the degree of microsegregation was similar at the two cooling rates resulting in no difference in solid fractions.

Porous aluminum is lightweight and has excellent shock absorption properties. It is expected to be used for automobile parts. In recent years, friction stir welding (FSW) has been used for welding automotive members. We have been attempting to fabricate porous aluminum using FSW. In this study, we placed laminated Al-Si-Cu ADC12 alloy die-casting plates (ADC12 plates) and blowing agent powder into the groove of an SS400 plate, then traversed the top tool on the ADC12 plates to mix the blowing agent powder into the ADC12 plates to fabricate a precursor. After traversing the top tool, we traversed the bottom tool from below the SS400 plate to foam the ADC12 precursor with the frictional heat generated while traversing the bottom tool. It was shown that a precursor can be fabricated at v＝10－50 mm/min by traversing the top tool. In addition, the obtained precursor can be sufficiently foamed with fine pores at a bottom-tool traversing speed of v＝20 mm/min.

The C15-Al₂Ca precipitates were observed using high-resolution transmission electron microscopy (HRTEM) to identify the coherency of the α-Mg/C15-Al₂Ca interface for the Mg-5Al-1.5Ca alloy aged at the temperature range from 548 to 598 K. The α/C15 coherent interface turned to the semi-coherent one by the introduction of misfit dislocations on the planar surface of the C15 precipitates for the alloy aged at 598 K for 1 h, whereas the coherency was maintained for the alloy aged at 548 K for 10 h. The curve showing the loss of interface coherency was drawn in the TTP diagram for the Mg-5Al-1.5Ca alloy, which is indicated that the α/C15 interface coherency has remained within 3.6×10⁷ s (10000 h) at 500 K.