In this study, we have examined the effects of the zincate pretreatment and heat aftertreatment on adhesion of electroless Ni–P coating onto aluminum alloy substrate.
The precipitation state of zinc was differs with the number of zincate treatment, and the double zincate treatment markedly improved the adhesion between aluminum alloy substrate and Ni–P coating. This adherent improvement can be attributed to metallurgical bond occurred by the diffusion between aluminum alloy substrate and Ni–P coating under the plating temperature (363 K×7.2 ks).

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In this study, the effect of high strain rate on the stress triaxiality is examined. The commercial 6061-T6 aluminum alloy which has wide applications as structural materials in the transport machine and construction industries is selected for this study. The response of the material to varying degrees of stress triaxiality under static and dynamic loading conditions is measured for circumferentially round-notched tensile specimens. Tensile tests are performed at RT with an Instron and servo hydraulic testing machines at three kinds of strain rates (ε=7.2×10⁻⁴, 1.0×10² and 1.0×10³ s⁻¹). Fracture surface observations and finite element method simulations also reveal the effect of stress triaxiality on the mechanical response under dynamic loading condition. The plastic constraint factors of the round-notched specimen under dynamic loading condition are lower than those under static loading condition. Stress triaxiality is decreased by the reflection of the stress wave near the notch root of the round-notched specimen under dynamic loading condition. The decrease of the stress triaxiality under the dynamic loading condition affects the relaxation of the plastic constraint in the round-notched specimens. The fracture surface of the round-notched specimen with the high stress triaxiality level shows the tensile fracture type under static loading condition. When the stress triaxiality decreases with increasing strain rate in the round-notched specimens, the fracture surface changes to the shear type. On the other hand, the temperature rise during impact tests hardly affects the relaxation of the plastic constraint in the round-notched specimens under high strain rates.

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In this study, we applied a halogen surface treatment to the AZ31B magnesium alloy in order to reduce the surface film thickness, and investigated the effect of the treatment on the ultrasonic weldability and brazeability of the magnesium alloy. The following results were obtained.
A halogen surface treatment by pickling the magnesium alloy into hydrofluoric acid successfully produced a thin and protective film of MgF₂ on the surface. The thickness of the surface film was less about one tenth and one third that of the specimen surfaces treated by wet polishing and dry polishing using emery paper, respectively.
The ultrasonic weldability of the magnesium alloy was improved by the halogen surface treatment and the cross tensile strength of the weld increased. The weld strength showed about three times and two times that with the specimens treated by wet polishing and dry polishing using emery paper, respectively. Furthermore, ductile fracture mode was observed on the fracture surface of the weld with the halogen-treated specimen.
Brazing filler metal hardly wet on the surface treated by wet polishing and dry polishing using emery paper, however, the brazing filler metal easily wet on the surface processed by the halogen treatment. The contact angle between the solidified brazing filler metal and the base metal was about 60 degree, and the halogen surface treatment improved the brazeability of the magnesium alloy.

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