Thin Au film was prepared by sputtering and evaporation methods with a quartz substrate, followed by microwave irradiation in air (frequency of microwave: 2.45 GHz, incident flux of microwave: 563 W, irradiation time: 600 s). As a result, it was confirmed that microwave heating of thin Au film is feasible. The growth of crystalline and particles due to microwave heating was confirmed from AFM observation and XRD analysis.Thin Au film is continuously heated during microwave irradiation, regardless of a preparation method of thin film. Microwave heating depends on the amount of microwave absorption on a thin Au film, which is related to the thickness and microstructure of the thin Au film. The rate of temperature rise depends on the ratio of a thickness to resistivity of thin Au film.
Thin Cu films with different thickness and microstructure were prepared using evaporation with a quartz substrate, followed by microwave irradiation in air (frequency of microwave:2.45 GHz, incident flux of microwave:563 W, irradiation time: 600 s). Microwave heating of thin Cu film is quite anomalous. The abrupt temperature rise and drop occur at early stage of microwave irradiation, then continuous temperature rise appears. The temperature change is caused by various combinations of the change in the rate of temperature rise (b.T) due to the ratio of a thickness to resistivity of thin Cu film, the increases in b.T due to Cu-oxide and resistivity rise at elevated temperature, and the decreases in b.T due to Cu particle growth during microwave irradiation and heat radiation from the surface of thin Cu film.
HIDEKI YAMAGISHI, JUNJI SUMIOKA, SHIGEKI KAKIUCHI, SHOGO TOMIDA, KOUICHI TAKEDA, and KOUICHI SHIMAZAKI The forge-welding process was examined to develop a high-strength bonding application of magnesium (Mg) alloy to aluminum (Al) alloy under high-productivity conditions. The effect of the insert material on the tensile strength of the joints, under various preheat temperatures and pressures, was investigated by analyzing the reaction layers of the bonded interface. The tensile strengths resulting from direct bonding, using pure copper (Cu), pure nickel (Ni), and pure titanium (Ti) inserts were 56, 100, 119, and 151 MPa, respectively. The maximum joint strength reached 93 pct with respect to the Mg cast billet. During high-pressure bonding, a microscopic plastic flow occurred that contributed to an anchor effect and the generation of a newly formed surface at the interface, particularly prominent with the Ti insert in the form of an oxide layer. The bonded interfaces of the maximum-strength inserts were investigated using scanning electron microscopy-energy-dispersive spectroscopy and electron probe microanalysis. The diffusion reaction layer at the bonded interface consisted of brittle Al-Mg intermetallics having a thickness of approximately 30 lm. In contrast, for the three inserts, the thicknesses of the diffusion reaction layer were infinitely thin. For the pure Ti insert, exhibiting the maximum tensile strength value among the inserts tested, focused ion beam-transmission electron microscopy-EDS analysis revealed a 60-nm-thick Al-Ti reaction layer, which had formed at the bonded interface on the Mg alloy side. Thus, a high-strength Al-Mg bonding method in air was demonstrated, suitable for mass production.
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