Minoru Hiramatsu

Laser surface alloying of zinc-nickel doubly electroplated films on steel

A new method has been developed in which zinc-nickel doubly-coated films were electroplated onto steel substrates and then irradiated, using a high powered YAG laser with kaleidoscope for surface modification to alloy the zinc-nickel films.

Influence of Zincate Treatment on Adhesion Strength of Electroless Nickel-Phosphorus Plated Film for Commercial Pure Aluminium

Characterizations of zincate films were conducted formed as a pretreatment for electroless nickel-phosphorus platings on commercial pure aluminum substrate (JIS A1050P-H24, 99.5 mass%Al). By using a basic solution which consists of sodium hydroxide and zinc oxide, a zincate film formed by the single zincate treatment showed coarse zinc grains of 1-2 μm in size. The double zincate treatment by using the basic solution reduced coarse zinc grains, and the thickness of the uniform zincate film was 20-30 nm. Iron-added zincate solutions decreased the number and the size of coarse grains in the single zincate treatments compared with the case of the basic zincate solution, and the double zincate treatments brought about further thin zincate films of ∼10 nm in thickness. The single zincate treatment by using the basic zincate solution resulted in poor adhesion strength of the electroless nickel-phosphorus plated film which peeled spontaneously off the substrate due to its residual stress. Quantification of adhesion strength by 90° peeling test showed the double zincate treatment by the basic solution increased the adhesion strength of the plated film up to 30 N/m. In the cases of the double zincate treatments by the iron-added zincate solutions, the adhesion strengths of the plated nickel-phosphorus films showed such remarkable increase that those could not be quantified by the peeling test due to the rupture of the plated nickel-phosphorus films. From the observation by transmission electron microscopy of the interfaces between the nickel-phosphorus plated films and the substrates, thickness of a zincate film ought to be ∼10 nm for eliminating gaps between the plated film and the substrate.

Corrosion Behavior of Electroplated Zn-Co Alloys from Sulfate Solutions

We studied corrosion by Zn-Co alloys electroplated from sulfate solutions onto iron substrate in a salt spray test (SST) by using scanning electron, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS).We found Zn-Co alloy surfaces corroded by SST to be covered by corrosion products (white rust) consisting of Zn(OH)2, ZnO, Zn5(CO3)2(OH)6, and ZnCl2·4Zn(OH)2 due to the dissolution of Zn. For γ-phase alloys consisting of 10∼20wt%Co, a corrosion product with low electrical conductivity (ZnCl2·4Zn(OH)2) formed mainly with the corrosion product apparently effective subsequently as a barrier against further corrosion. The good corrosion resistance of γ-phase films can be attributed to conversion to a more noble-metal site due to Co concentrating on the corroded surface as corrosion advanced.

Rubber adhesion of an electroplated zinc-silica dispersion coating.

シリカ分散亜鉛めっきとゴムとの接着性を, めっき表面の形態及びシランカップリング処理の面から検討した. 高さ約7μmの凹凸を有する亜鉛及びシリカ分散亜鉛めっきのゴム接着強さは, 平滑状の亜鉛及びシリカ分散亜鉛めっきに比較して, 2～5倍大きく, 凹凸形状によるアンカー効果が認められた. しかし, 接着の破壊状態は, めっき表面からのはく離割合が大きい. シランカップリング処理を施した凹凸状シリカ分散亜鉛めっきの塩水噴霧試験100時間後のゴム接着強さは, 初期のものと同レベルの接着強度を維持し, めっき表面からの破壊割合もほとんどゼロとなった. また, プライマーを使用しなくても, シランカップリング処理したものでは相当強固な接着性を示すことを認めた.