Application of displacement-load control to vacuum free self-induced fusion solidification bonding of aluminum with copper insert metal was investigated in this study. Vacuum free bonding requires the fracture of the oxide film and the contact of the clean surfaces, because the oxide film on the bonding interface acts as the anti-bonding factor. The displacement-load control method by set bonding load controlled maximum contact pressure in the cyclic deformation between the solid bonding surfaces. Cyclic contact of the solid surfaces occurred the fracture of the oxide film which formed on the surface. The displacement-load control promoted vacuum free bonding than the static load method by the weight. Bonding area ratio increased with the increase of bonding time and insert metal thickness. Set bonding pressure also increased the bonding area ratio. Evaluation for the effect of the set bonding pressure on the change of bonding area ratio suggests that the effective minimum bonding pressure which occurs the fracture of the oxide film will be exists.
Deformation behavior of high-purity aluminum wiring ribbons during ultrasonic bonding was investigated using a laser-Doppler vibrometer, a high-speed laser displacement sensor, and a high-speed video camera. The displacement of the flat-bottom wedge tool was referred to as the index for the deformation of the ribbon. The deformation of the ribbon by applying the bonding force completes immediately. The deformation restarts by the application of the ultrasonic vibration. The deformation induced by ultrasonic vibration does not contain elastic component. Fine initial bond areas are first extended to the direction of the ultrasonic vibration and then they are expanded to the lateral direction. Finally, the bond areas coalesce with each other to form a continuous bond area.
Joining process and wavy interface formation behavior in explosive welded Cu/Al joints were investigated both numerically and experimentally. First, detonation of the explosive was simulated by Euler-Lagrange coupling method. Change in impact velocity and impact angle at the collision point during detonation was examined using a series of gauge points. Secondly, the numerical analysis of wavy interface formation was performed by using Smoothed Particle Hydrodynamics (SPH) method under the obtained impact velocity and impact angle conditions. The metal jet emission and wavy interface formation were clearly reproduced by the simulation. The Cu/Al lap joints were also fabricated by the explosive welding under the same condition. Microstructure observation revealed that the wavy interface including the intermediate phase layer was formed. The simulation results (wave amplitude and wave length) showed a good quantitatively agreement with the experimental results.
The solid state bonding of fine-grained high carbon steel with different initial void shapes (surface asperities) was carried out. The contacting modes and predominant bonding mechanisms were investigated. The interfacial contacting process was influenced by the geometrical factor: initial void shape with the surface asperity angle α0. The surface asperity angle changed the initial void shape on the bonding interface. When α0 = 10 ～ 15 deg, the initial void shape was Lens-type. While α0 = 40 ～ 45 deg, it was Massif-type by the observation of cross section on the bonding interface. Lens-type contacting process was controlled by surface folding mode, which showed a high bonding rate. On the other hand, Massif-type contacting process was controlled by both surface folding and interfacial expansion modes, which inhibited the contacting rate. In spite of two modes, it was found that superplastic deformation could be the predominant bonding mechanism if the bonding conditions, temperature and pressure were appropriate. In other words, it was identified from the stress exponent n value and the activation energy Q value of each bonding mechanism that superplastic flow played a dominant role in the interfacial contacting process from a bonding ratio of 30% to 40%, under the conditions of bonding temperature T = 1023 ～ 1053 K and bonding pressure P = 35 ～ 45 MPa.
Ni thin film (～20 nm) was uniformly formed on p-GaN substrates by radio frequency magnetron sputter deposition method. In order to improve the conductivity and electrical contact properties of Mg-doped p-GaN, the enhancement of H release from Mg-doped p-GaN was attempted by applying current flow through the substrates during low temperature annealing at 573 K and 673 K. The microstructure and electrical properties after the annealing were then analyzed by transmission electron microscopy observation, direct current conduction tests and Hall effect measurement tests. The results reveal that no reactions occur at the interface between deposited Ni film and p-GaN substrate during annealing at 573 K for 3600 s. The electrical conductivity of p-GaN shows higher improvement by applying current flow during annealing at 573 K and 673 K, compared to annealing without the current flow. To investigate the effect of applying current flow during annealing, the current values of the samples during annealing with and without applying current flow were measured and they were compared. The mechanism of H release from p-GaN by applying current flow during annealing were discussed.
The aging behaviors of Al-10%Si-Mg system alloys cast by permanent mold were investigated by optical microscopy, scanning electron microscopy and micro-vickers hardness measurement. With increasing Mg content from 0.05% to 0.9%, the peak aged hardness in T5 treatment were increased due to increase number density of precipitation. When demold temperatures were increased from 323K to 773K, the peak aged hardness in T5 condition were increased. This tendency was affected by existence of rod-like precipitations after as-cast state. By the amount decreased in the solubility of Mg in the matrix, the crystallization of Mg-including phases (e.g., π -Al8Si6Mg3Fe and Mg2Si) decreased or disappeared and brought some influence for age hardenability of the alloy castings.
Age hardening characteristics of Mg-Al-Mn system alloys cast in to iron mold were investigated by means of hardness measurement and microstructure observation with optical microscopy. As for the age hardening behavior of the Mg-Al-Mn system alloys, peak-age hardness was increased with increasing the aluminum content in all aging temperature, and the peak-age time was shifted to the side for a short time remarkable. Pre-precipitation area was not observed in AM60 magnesium alloy iron mold castings in the condition of over-aged contrastively in AM60 magnesium alloy sand mold castings. Age hardening behavior of Mg-Al-Mn system iron mold castings depended on the cellular precipitation with increasing the aluminum content and aging temperature, as a result of hardness measurement in cellular and intragranular precipitation phases for AM60, AM80 and AM90 magnesium alloys.