Makoto Hino

Influence of SiO2 Nanoparticle Codeposition on Homogeneity of Zinc-Nickel Alloy Plating from an Acid Sulphate Bath

Zinc-nickel-SiO2 electrodeposits have been produced from an acid sulphate bath. Thecodeposition behavior of SiO2 and the homogeneity of platings were examined. The presence ofSiO2 nanoparticles in the plating bath appears to change the alloy deposition behavior. Rate ofnickel deposition was considerably decreased with SiO2 nanoparticles in the bath. The homogeneityof platings between zinc and nickel were improved by adding the SiO2 nanoparticles in the bath. Atan early stage of electrodeposition, it seems that the SiO2 nanoparticle acts as a nucleus of theprecipitation. The SiO2 nanoparticle has not uniformly dispersed in a plating film, but distributedonly in the SiO2 rich layer with about 50 nm in thickness formed beneath the surface. In addition,this SiO2 rich layer can improve the anticorrosive performance. Therefore, the zincic use can besuppressed, because film thickness can be more thinned, compared with zinc and zinc-nickel alloyelectroplating.

Effect of Electroless Ni-P Plating on Mechanical Properties of Al-4%Ge Alloy

In this study, the effect of electroless Ni-P plating on the mechanical properties of Al-4%Ge alloy was investigated. As the results, the following points were clarified. (i) Tensile strength of the specimen subjected to the Ni-P plating after aging treatment or furnace cooling treatment was improved by about 10% in comparison to one of the non-processed specimens. (ii) Breaking elongation of the specimen subjected to the Ni-P plating after aging treatment showed no significant changes in comparison to one of the non-processed specimens. On the other hand, breaking elongation of the specimen subjected to Ni-P plating after a furnace cooling treatment was reduced to 70% in comparison to one of the non-processed specimens. (iii) Fatigue strength of the specimen subjected to the Ni-P plating after a furnace cooling treatment was overall reduced rather than one of non-processed specimens. (iv) Fatigue strength of the specimen subjected to the Ni-P plating after aging treatment was overall reduced, except for the low-stress region, rather than one of the non-processed specimens. (v) In the specimen subjected to Ni-P plating after a furnace cooling treatment or aging treatment, clear hydrogen desorption was recognized. On the other hand, there was only hydrogen desorption from a few of the non-processed specimens. Especially, it is considered that the poor fatigue strength and ductility of the plating materials are mainly due to the interaction between the surface precipitates and hydrogen gas.

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.

Plating on Developed Al-Mg-Zn Alloy Casting and its Glossiness

The purpose of this study is to develop an Al-Mg-Zn series aluminum alloy casting suitable for the plating. We evaluated the influence of the metal structure on the plating process of both AC4CH and a developed aluminum alloy and then examined their suitability to plating. With the AC4CH-T6 casting containing the silicon, it was difficult to obtain a smooth surface by pretreatment process because of the surface irregularity between the hard and chemically stable eutectic silicon and the aluminum matrix. On the other hand, with the developed silicon-free alloy casting, it was possible to produce a smooth surface by pretreatment process, and this glossiness was superior to that of the AC4CH-T6 casting after electroless Ni-P plating. Furthermore, the plating property of the developed casting was also superior to that of the AC4CH-T6 casting, because the zinc deposit on the developed casting from the zincate treatment became uniformly, depending on the uniform displacement reaction.

Effect of Heat Treatment Conditions and Small Addition of Cu on Occurrence of Serration in Al-Si Alloys

In this study, the effect of heat treatment conditions and small addition of Cu on occurrence of serration in Al-Si alloys was investigated. Specimens were aged for various times up to 87ks at 273K or 473K after quenching from 853K, and tensile-tested at room temperature. In the binary alloy, serration was observed even after aging for 87ks at 273K, while in the case of aging at 473K, serration did not occur under aging conditions at aging time, tA≧20s. On the other hand, serration was observed even after aging for 72ks at 473K in the Cu-added alloy. In both alloys, serration was also recognized when the specimens were furnace-cooled from 853K to room temperature. Thus, for aging at 473K of the binary alloy serration was observed only when the aging period was short enough, but addition of Cu to the binary alloy prolonged the aging period where serration could be recognized. Aging rate of both alloys measured by tensile strength was almost the same. The size of precipitates in the Cu-added alloy was smaller than that in binary alloy. Moreover, the number of the precipitates at the grain boundary in the Cu-added alloy was smaller than that in the binary alloy. It is considered that serration occurs for Al-Si alloys when the specimen is heat-treated so that small precipitates may be formed. Now the details of the effect of Cu addition are not clear.

Effect of Electroless Ni-P Plating on the Fatigue Strength of Dilute Al-Si Alloys

In this study, the effect of electroless Ni-P plating on the fatigue strength of dilute Al-Si alloys was investigated. As results, the following points were clarified. Fatigue strength of the specimen subjected to zincate treatment only after furnace cooling treatment was almost the same as the furnace cooling only. Fatigue strength of the specimen subjected to Ni-P plating after furnace cooling treatment, was reduced overall, except for high-stress region, rather than one of non-processing materials. Fatigue strength of the specimen subjected to Ni-P plating after aging treatment showed a clear increase in comparison with one of non-processing materials. Breaking elongation of the specimen subjected to Ni-P plating after aging treatment showed no significant changes in comparison with one of non-processing materials. On the other hand, breaking elongation of the specimen subjected to Ni-P plating after furnace cooling treatment reduced by half in comparison with one of non-processing materials. Especially, it seems that poor fatigue strength and ductility of plating materials are mainly caused due to interaction between surface precipitates and hydrogen gas.

Serration and Reversion Treatment in Al-Zn Alloys

Aging phenomena of Al-Zn alloys have been much investigated and many studies have been made on the change of mechanical properties on aging. Appearance of saw-tooth yielding (serration) in the stress-strain curve of tensile deformation has been reported in several reports. In this study, the relationship between occurrence of serration and reversion heat treatment was studied by tensile test on Al-Zn alloys. Serration was observed for the furnace cooled specimen, but not for the as-quenched one and the shortly aged one, which result is difficult to be interpreted by the Cottrell theory. The stress amplitude in the serration increased with increasing the time of annealing for reversion and then stayed at a constant value which might be interpreted by the Cottrell theory. The stress amplitude in the serration decreased with increasing the annealing temperature, which is contrary to the prediction by the Cottrell theory. The specimen directly annealed without aging and the one annealed after aging agreed well with each other in the tensile strength and the stress amplitude in the serration, which suggests solute clusters as the cause of serration.