Effect of gap length on welding characteristics of 2000 series aluminum alloy sheets in magnetic pulse welding (MPW) was investigated. Collision time for the 2017-T3 sheet welded at gap length of 1.2 mm and 4.6 mm were 6.16 µs and 16.9 µs respectively, which were increased with increasing of gap length. The collision speed calculated from collision times increased as the gap length increased, showed a maximum value of 380 m/s with a gap length of 2.0 mm, and then the speed declined. This result indicates that it is possible to join sheets at a higher collision speed even with the same discharge energy by adjusting an appropriate gap length. Strong lap joint was achieved for the 2024-T3/2024-T6 and the 2024-T3/7075-T6 lap joint sheets by welding condition of gap length more than 1.0 mm. Thus, it could be possible to improve the weld strength by widening the gap length and performing MPW at high collision speed. SEM and HAADF-STEM observations showed no clear oxide films formed on the weld interface. From microstructure observation, it was considered that lap joints fabricated by MPW were welded at solid state.

Magnesium is an essential element for human health and is a suitable material for bio-absorbable implant because the risk of hypermagnesemia is quite low. In recent years, a number of studies have been carried out using bio-absorbable materials for implantable scaffolds. It is desirable the device performance can be tailored to the anatomical site in which the device is implanted, so the key problem for these devices was to control the corrosion rate of magnesium. However, the effect of the blood flow over the devices on the corrosion behavior is not obvious yet. In the present study, we investigated the corrosion behavior of various specimens immersed in fluid flows. The corrosive environment was reproduced by pulsatile flow of NaCl solution representing blood flow in the human body. It was found that the corrosion behaviors of the specimens were strongly affected by the induced strain, the surface condition and the flow rate. In contrast, the change in the fluid flow characteristics such as laminar flow and turbulent flow had less strong effect on the corrosion behavior.

The effect of homogenization conditions (heating and cooling rates) on phase transformation and precipitation behavior of 3004 aluminum alloy during annealing was investigated with X-Ray diffraction/Rietveld refinement. Mass fraction of Al matrix, Al₆(Mn,Fe) and α-Al₁₂(Mn,Fe)₃Si before and after annealing at 723 K was examined by X-ray diffraction (XRD) and Rietveld refinement technique. Powderization of samples was useful to eliminate the effect of prefered orientation (texture) and coarse crystal grains on diffraction intensity. As a result, mass fraction change of phase transformation of primary particles and precipitation during annealing at 723 K was successfully evaluated. More precipitates due to slow heating and cooling rate for the homogenization treatment influence microstructures and mechanical properties in the latter process, such as work hardening, anneal softening and precipitation during annealing. With applying this knowledge, desirable microstructures and mechanical properties can be obtained.