Effects of Zn and Mg contents in Al–Zn–Mg alloys with Mn and Ag additions on the microstructures and mechanical properties were investigated. The increase in Zn content largely contributed to the increase in age hardenability of the alloy through the fine precipitation in grains, and the subsequent increase in Mg content contributed little to the increase in age hardenability. Tensile strength at the peak-aged condition increased with increasing Zn and Mg. On the other hand, the elongation decreased and the main fracture mode changed from transgranular fracture to intergranular fracture. The size of grain boundary precipitates of Zn–Mg alloys became lower by low temperature aging and two-step aging, which enables to increase both tensile strength and elongation, showing that mechanical properties can be improved by decreasing the grain boundary precipitate size even in the alloys to which Zn and Mg are added.

Tool wear and wear mechanism of carbide cutting tool in turning Al–Si alloy diecastings were investigated. Decreasing amount of coarse primary silicon was effective for reducing cutting resistance and cutting tool wear. New hyper-eutectic Al–Si system alloy which doesn’t contain coarser silicon particles provided good turning machinability equivalent to conventional eutectic Al–Si system alloy. In case of increasing feed rate from 0.05 to 0.10 mm/rev, cutting tool wear of conventional hyper-eutectic Al–Si system alloy increased. On the other hand, that of eutectic Al–Si system alloy decreased, and that of new hyper-eutectic Al–Si system alloy didn’t changed. Built-up edge and aluminum deposit on the flank wear land were observed in all aluminum alloys.

Influences of solute atoms and their contents on the uniform elongation were investigated using Al–Mg and Al–Si alloys respectively. Dislocation characteristics of both alloys were examined by X-ray diffractometry and transmission electron microscopy. In the case of solute concentration ranging between 0.3 and 1.6 (mass%), it was found that the increase of solute concentration caused the decrease of the uniform elongation for the case of Al–Mg alloys, whereas the increase of that for the case of Al–Si alloys. It was suggested that the solute Mg in aluminum caused a strong interaction on dislocation with comparison to the solute Si, which probably caused the large increase of dislocation density during the tensile deformation. It is considered that the solute Si has stronger effect of decreasing the stacking fault energy of the aluminum alloy than the solute Mg. Thus, as for Al–Si alloys, the increase of the work-hardenability and the uniform elongation may occur by retardation of the dynamic recovery during the tensile deformation.

The increase in Zn or Mg content results in an increase in Al–Zn–Mg alloys strength, however they become more susceptible to hydrogen embrittlement. To understand the hydrogen embrittlement behavior, it is necessary to study the hydrogen trapping behavior. In the present study, Al–8%Zn–1%Mg was made in order to have six trap sites (vacancies, dislocations, grain boundaries, particles, precipitates and micropores) and hydrogen trapping behavior in those trap sites was assessed by means of thermal desorption analysis (TDA). In addition, micropores were evaluated in detail using X-ray microtomography. Hydrogen desorption energies from grain boundaries and micropores were calculated using TDA curves. These values were 2 to 3 times larger than the ones reported in the literature due to a change in the trap sites during thermal desorption test. Increase in the number density of micropores was observed above 673 K during thermal desorption experiment. As the temperature increases, it has been reasonably inferred that some hydrogen desorbed from trap sites are released from the specimen and the rest of hydrogen is redistributed to form new micropores. It is revealed that low heating rate induces a change in trap sites and affect the measurement of hydrogen desorption energies.