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Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Okano M.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Takamizawa M.,OM Sangyo Co. | Nakai K.,Ehime University
Materials Transactions | Year: 2010

Generation and growth of whiskers and nodules from electroplated tin and tin-lead films on copper or nickel substrates were studied by scanning electron microscopy and X-ray diffraction. In the case of copper substrates, whiskers were formed in 0.3 Ms on the tin film whose thickness was 1 μm. On the other hand, tin-lead films on copper substrates showed only nodules even after 13 Ms. Residual stress of the tin film (1 μm) and the number of whiskers increased with the amount of copper-tin intermetallic compounds (Cu6Sn 5) which developed between the plated film and the copper substrate. Although residual stress and the amount of Cu6Sn5 also increased in the tin-lead system, the morphology of the layer of Cu 6Sn5 was more uniform compared with the case of tin films on copper substrates. When the tin-lead film was subjected to the compression testing by a ball of zirconium oxide (1 mm-diameter, 2.94 N-0.605 Ms), the edge of the indentation did not show any whiskers but diffusion of lead was observed from right under the zirconium oxide ball to the fringe, as well as Ostwald growth of lead. In the case of the tin film on the nickel substrate, whose residual stress was weakly tensional, nickel-tin intermetallic compounds (Ni3Sn, Ni3Sn2, Ni3Sn4) uniformly developed immediately after electroplating, and no whiskers were observed even after the compression testing. While growth of whiskers is considered to be due to diffusion of tin atoms induced by inhomogeneous strain field in the electroplated film, lead atoms in tin-lead system is considered to diffuse rapidly toward the free surface to release residual stress and to generate many nodules. © 2010 The Japan Institute of Metals.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Ushio M.,Okayama University of Science | Yokomizo D.,Okayama University of Science | Kanadani T.,Okayama University of Science
Keikinzoku/Journal of Japan Institute of Light Metals | Year: 2012

Formation of zincate films and adhesion of electroless nickel-phosphorus plated films were studied for binary aluminum alloys of Al-2at%Mn, Al-2at%Fe, Al-2at%Cu, Al-2at%Zn and high-purity aluminum (99.999 mass%) Precipitation mode of zinc in the zincate treatmens greatly varied according to the alloying elements in the substrates. In the cases of the first and the second zincate treatments for Al-Mn, Al-Fe and high-purity aluminum, zinc precipitated excessively, then, porous films of zinc repeatedly fell off the substrate. The surfaces of Al-Cu and Al- Zn alloys were immediately coated by uniform zincate films in the first and the second zincate treatments. Precipitation of zinc is considered to be uniform if the oxide film on a substrate dissolves uniformly and rapidly in the zincate solution. When electroless nickel-phosphorus plating was conducted after the second zincate treatment of Al-Mn and Al-Fe alloys, the plated films easily peeled off. Those on Al-Cu and Al-Zn alloys showed excellent adhesion, and dimple patterns of the substrates were observed on the partly peeled areas. The poor adhesion is thought to be caused because the excess zinc dissolves at the beginning of the plating and generates hydrogen gas, then, gaps are formed between the plated films and the substrates.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Hiroshima Institute of Technology | Nagata N.,Surtech Nagata Co. | Kanadani T.,Okayama University of Science
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals | Year: 2013

Effect of alloying elements and generation of hydrogen gas dining zincate treatment and electroless nickel-phosphorus plating were studied by using electron microscopy. Hydrogen gas was vigorously evolved during the zincate treatment for binary Al-2 at%Mg and Al-2 at%Si alloys, and the zincated surfaces were nonuniformly covered with excess coarse zinc particles, due to continuing oxidation of the substrate and reduction of proton and zincate ions. On the other hand, the surfaces of ternary Al-2 at%Zn-0.2 at%Mg and Al-2 at%Zn-4.5 at%Mg alloys were immediately covered with thin and uniform film of zinc. Magnesium in aluminum alloys and the excess precipitation of zinc were found to lower adhesion of electroless nickel-phos-phorus plated films. When the zincated Al-2Mg and A1-2Si alloys were immersed in the plating solution dissolution of the excess zinc generated hydrogen gas and the plated films poorly adhered to the substrates. Despite the thin and uniform zincate film the plated film on Al-2Zn-4.5Mg alloy was easily peeled due to the voids formed between the plated film and the substrate. Magnesium in the alloy may suppress precipitation of nickel and accelerate generation of hydrogen gas at the beginning of the plating. ©2013 The Japan Institute of Metals and Materials.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Ushio M.,Okayama University of Science | Ushio M.,Hiroshima Aluminum Industry Co. | And 3 more authors.
Materials Transactions | Year: 2013

The formation of zincate films and the adhesion of electroless nickel-phosphorus plated films on binary aluminum alloys of Al-2at% Mn, Al-2at% Fe, Al-2at% Cu, Al-2 at%Zn and high-purity aluminum (99.999 mass%) were studied. The precipitation mode of zinc during the zincate treatments significantly varied according to the alloying elements in the substrates. For the first and second zincate treatments of AlMn, AlFe and high-purity aluminum, the zinc excessively precipitated, then porous films of zinc repeatedly fell off the substrate. The surfaces of the Al-Cu and Al-Zn alloys were immediately coated by uniform zincate films during the first and the second zincate treatments. The precipitation of zinc is considered to be uniform if the oxide film on a substrate uniformly and rapidly dissolves in the zincate solution. When an electroless nickel-phosphorus plating was conducted after the second zincate treatment of the AlMn and AlFe alloys, the plated films easily peeled off. Those on the AlCu and Al-Zn alloys showed excellent adhesion, and dimple patterns of the substrates were observed on the partly peeled areas. The poor adhesion is thought to be caused due to the fact that the excess zinc dissolves at the beginning of the plating and generates hydrogen gas, then gaps are formed between the plated films and the substrates. © 2013 The Japan Institute of Metals.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Mitooka Y.,Industrial Technology Research Institute of Okayama Prefectural Government | Kanadani T.,Okayama University of Science
Keikinzoku/Journal of Japan Institute of Light Metals | Year: 2011

In order to clarify the mechanism of formation and growth of nodules and whiskers on the leads used in aluminum electrolytic capacitors, aluminum-tin binary alloys were subjected to the investigation as the model alloys for the joints in the leads. The concentration of tin in the binary alloys was 1, 5 or 10 at%. The alloy of 10 at% tin showed the largest number of nodules or whiskers on its polished surface after keeping under ambient conditions for 7.8Ms. Many whiskers whose length were more than several tens of micrometers were observed in the case of the alloy of 5 at% tin. The alloy of 1 at% tin showed few nodules or whiskers. Growth of nodules and whiskers is caused by difusion of tin atoms from the strained or unstable areas into the stable ones or the root grains. Then, the extrusion toward the surface at the root grains develops nodules and whiskers. As a prevention measure of whiskers, selective etching of the aluminum phase using a solution of sodium hydroxide was confirmed to be successful. Thus the aluminum phase was thought to form a non-uniform distribution of strain in the tin phase. This acts as the driving force in difusion of tin atoms.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Saijo A.,Hori Metal Finishing Industry | Kanadani T.,Okayama University of Science
Materials Science Forum | Year: 2010

Corrosion protection by anodization and conversion treatment in phosphate solution was studied by microstructural and electrochemical analysis. Both the anodized and the conversion-treated layers showed sacrificial protection in a solution of sodium chloride. The corrosion current or the dissolving rate of the anodized layer was smaller than that of the conversion-treated surface. The modified layers had another mode of protection to form protective films on magnesium substrate where the original modified layers were mechanically lost. Since the state of magnesium in the anodized layer is close to magnesium oxide, phosphorus in the layer is considered to have an important role in these properties concerning the above corrosion protection. © (2010) Trans Tech Publications.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Furukawa R.,Okayama University of Science | Furukawa R.,Japan Steel Works | Kanadani T.,Okayama University of Science
Materials Transactions | Year: 2010

Zincate treatment and electroless nickel-phosphorus plating for aluminum alloys of Al 100, A2017, A5052 and A7075 were researched from the viewpoints of alloying elements and activation conducted prior to zincate treatment. Surface morphologies of zincated surfaces, electrochemical properties during zincate treatment and depth profiles on activated and zincated surfaces were investigated by microscopy and measurement of temporal changes of electrode potential. Adhesion strengths of the plated films were measured by 90° peeling test, which showed that double zincate treatment improved adhesion strength especially when ferric ion was added into the zincate solution except for the case of A7075. Temporal changes of electrode potential during zincate treatments and morphologies of the zincated surfaces showed that copper and zinc promoted uniform precipitation of zinc and resulting rapid termination of conversion reaction. Excess zinc was shown to dissolve into the plating solution and cause the formation of lowdensity area or gaps between plated films and substrates. Activation for Al100 by various conditions showed that formation of oxide film had a remarkable effect on precipitation of zinc during zincate treatment. When a mixture of nitric and hydrofluoric acid was used for activation, finer particles of zinc were formed near etch pits compared with the cases of hydrochloric or nitric acid. On the other hand, the surface was uniformly covered with fine zinc particles in the case of the activation with a solution of sodium hydroxide. This indicates that uniformity of oxide film on substrate before zincate treatment is thought to bring about uniform precipitation of zinc. © 2010 The Japan Institute of Light Metals.


Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government | Hino M.,Industrial Technology Research Institute of Okayama Prefectural Government | Furukawa R.,Okayama University of Science | Kanadani T.,Okayama University of Science
Keikinzoku/Journal of Japan Institute of Light Metals | Year: 2010

Zincate treatment and electroless nickel-phosphorus plating for aluminum alloys of A1100, A2017, A5052 and A7075 were researched from the viewpoints of alloying elements and activation conducted prior to zincate treatment. Adhesion strengths of the plated films were measured by 90° peeling test which showed that double zincate treatment improved adhesion strength especially when ferric ion was added into the zincate solution. Temporal changes of electrode potential during zincate treatments and morphologies of the zincated surfaces showed that copper and zinc in the substrates promoted uniform precipitation of zinc. Excess zinc was shown to dissolve into the plating solution and cause formation of low-density areas or gaps between plated films and substrates. Activation for A100 by various conditions showed that formation of oxide film remarkably affected the precipitation of zinc. When a mixture of nitric and hydrofluoric acid was used for activation, finer particles of zinc were formed near etch pits compared with the cases of hydrochloric or nitric acid. On the other hand, the surface was uniformly covered with fine zinc particles in the case of the activation with a solution of sodium hydroxide. This indicates that uniformity of oxide film on substrate before zincate treatment is thought to bring about uniform precipitation of zinc.


Fukuta T.,Okayama Prefectural University | Obunai K.,Okayama Prefectural University | Ozaki K.,Okayama Prefectural University | Tanabe A.,Okayama Prefectural University | And 3 more authors.
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals | Year: 2015

The purpose of this study is to investigate the hydrogen embrittlement property of an Al-Mg-Zn series of alloy and to propose the effective concepts to prevent the hydrogen embrittlement for automotive wheels which have shiny appearance without plating. The three types of casted an Al-Mg-Zn series of alloys in which weight fraction of Zn was 3.1, 3.4 and 4.1 mass% were prepared to discuss the effect of Zn fraction on its hydrogen embrittlement characteristics. T6 treatment was applied these alloys to improve its mechanical properties. The hydrogen embrittlement characteristics were evaluated by constant load tensile test under constant temperature. 1 mass% of NaCl solution was dropped to notch of the specimen to evaluate the time until fracture under controlled corrosive environment. Hydrogen generation under corrosive environment and microscopic segregations of materials were also evaluated. Test results were as follows: The rate of diminution in tensile strength at corrosive environment was increased with the increase of the weight fraction of Zn. Microscopic observation showed that the hydrogen generation was active at around the segregation and the number of segregations was increased with the increase of the weight fraction of Zn. According to these results, a reduction in the number and size of segregation is an effective way to prevent hydrogen embrittlement. © 2015 The Japan Institute of Metals and Materials.


Akazawa S.,Okayama Prefectural University | Fukuta T.,Industrial Technology Research Institute of Okayama Prefectural Government | Obunai K.,Industrial Technology Research Institute of Okayama Prefectural Government | Ozaki K.,Industrial Technology Research Institute of Okayama Prefectural Government | Murakami K.,Industrial Technology Research Institute of Okayama Prefectural Government
Keikinzoku/Journal of Japan Institute of Light Metals | Year: 2015

The purpose of this study was to improve tensile properties by grain refinement technique for injection molding of magnesium alloy by using solid carbon materials. A solid carbon material of Carbon Black was attached to surface of AZ91D alloy chips by using ball-milling. AZ91D alloy chips and Carbon Black were mixed while heating and stirring in the cylinder of magnesium injection molding machine, then molten metal was injection molded to 2.5 mm thick flat plate. The mechanical characteristics of molded products were evaluated uniaxial tensile load. The tensile test result showed that the 0.2% of proof stress, tensile strength and fracture strain were improved by Carbon Black addition. Microstructure observation revealed that the grain size of molded products were progressively finer when Carbon Black addition was increased. These results suggested that the addition of appropriate amount of Carbon Black is effective to improve the tensile properties of AZ91D alloy. © 2015 The Japan Institute of Light Metals.

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