Yutaka Mitooka

Effects of zincate treatment on adhesion of electroless Ni-P coating onto various aluminum alloys

Abstract The effects of alloying elements on zincate treatment and adhesion of electroless Ni-P coating onto various aluminum alloy substrates were examined. Surface morphology of zinc deposits in the 1st zincate treatment and its adhesion were changed depending on the alloying element. The zinc deposits in the 2nd zincate treatment became thinly uniform, and the adhesion between aluminum alloy substrate and Ni-P coating was improved irrespective of the alloying element. XPS analysis revealed the existence of zinc on the surface of each aluminum alloy substrate after the pickling in 5% nitric acid. This zinc on the surface should be an important factor influencing the morphology of zinc deposit at the 2nd zincate treatment and its adhesion.

Mechanism of Whisker Growth Suppression by Lead Co-Deposition on Electroplated Tin Film

This study investigated the effect of lead on the whisker growth of a tin film that was the electrodeposited on a phosphor bronze substrate. Subsequent FE-AES observation revealed that the whisker growth on the electrodeposited tin film varied depending on the morphology of the oxide film. The whisker growth was suppressed concomitantly with thinness or fragility of the oxide film formed on the tin deposits. The whisker growth was also suppressed concomitantly with the lead co-deposition in the tin deposits. In the Sn/Sn-Pb multilayer, because the lead between the tin film and the substrate was transferred to the surface, the whisker growth was also suppressed. This whisker growth suppression effect caused by the existence of a lead in the tin deposits was attributed to the oxide film thinning and embrittlement, depending on the lead transfer to the surface at room temperature.

Development of Laser Surface Treatment with Excellent Corrosion Resistance and Conductivity Performance on Magnesium Alloy Products

Effects of the laser processing on corrosion resistance and conductivity for the magnesium alloy products anodized from the phosphate electrolytic solution were examined. The area where anodized coating was removed under the appropriate laser processing condition showed the excellent corrosion performance as well as good conductivity. This improvement of the conductivity is attributable to the removal of the anodized coatings whose conductivity is not good, and excellent corrosion resistance is based on the sacrifice corrosion protection by anodizing from the phosphate electrolytic solution.

Influence of Carbon Addition on Mechanical Properties of Thixomolded Magnesium Alloy

For the purpose of application for structural members such as the automobile, effect of carbon modification to the AZ91D magnesium alloy chip surface on fatigue property was examined by the rotary bending test. The carbon modification to the chip surface was quite useful for the control of the internal defect for the thick part on the thixomolding process. The depression of the internal defect by the carbon nanoparticle modification is closely related to the improvement of flowability, and that is presumed to be based on promoting the filling of the molten metal into the metal die inside. The tensile strength and elongation were respectively improved by the carbon addition. In addition, the fatigue strength also improved over 15%. This improvement of the mechanical property is based on the refinement of the crystal grain as well as the depression of the internal defects.

Laser Joining of Metal and Plastic Using Insert Materials

Laser joining for dissimilar materials between metals plate and polypropylene plate using a newly developed insert sheet was investigated. It was not possible to join the plate of various metals to the nonpolar plastic plate such as the polypropylene directly under the various laser-irradiation conditions. However, the use of insert sheet held between the metal plate and the polypropylene plate made it possible to join each metal plate to polyethylene plate by laser-irradiation. The joining strength increased with the increase in the input energy by laser-irradiation, and the joining strength cloud be improved since the reactivity between each metal and the insert material allows improvement by giving the insert material polarity with such as a-NH2 group, -COOH group.

Laser Irradiation on Tin Electroplating and Whisker Suppressibility

Tin electroplating with its excellent solderability and low cost performance is garnering attention as a lead-free technology. However, tin electroplated film is plagued with the issue of whisker formation. In this research, in order to suppress the whisker formation, the effect of laser irradiation on tin electroplated film onto a phosphor bronze substrate was studied by scanning electron microscopy and focused ion beam microscopy. Whiskers and nodules were generated on the surface of the tin electroplated film for a short time after electroplating. However, laser irradiated specimens showed no whiskers as well as nodules. This whisker suppression is attributable to the formation of thinly uniform intermetallic compound layer. Moreover, the solderability of the laser irradiated specimen was superior to that of the reflow specimen. These results demonstrated the effectiveness of laser treatment.