6061-T6 aluminum alloys (Al-Mg-Si alloys) are known to show low environmental hydrogen embrittlement sensitivity. However, this alloy containing 0.1% of iron shows a decrease in ductility when a large amount of hydrogen is previously charged in an atmosphere containing water. In this study, we investigated the effect of electroless Ni-P plating involved the removal of oxide film on the absorption of hydrogen and the hydrogen embrittlement sensitivity of a 6061-T6 aluminum alloy. It was shown that the ductility decreased immediately after Ni-P plating because a large amount of hydrogen was introduced into the alloys. In addition, the hydrogen embrittlement sensitivity changed according to the holding time after Ni-P plating at room temperature. The 6061-T6 alloy showed better resistance for hydrogen embrittlement when the alloy was kept at room temperature for 50 days after Ni-P plating.
Plastic behaviors of A5052-O sheet subjected to the uniaxial and biaxial tensions and the reverse and cross loadings were measured. In the reverse loading, the reyield stress and the flow stress are lower than the monotonic flow stress; the specimen exhibits the Bauschinger effect. In the cross loading, the change in the strain path results in an increase in the flow stress and a decrease in the work hardening rate. Plastic behaviors of the specimen were simulated by using a polycrystal plasticity model. It is found that the latent hardening coefficient and the back stresses of slip systems have no influence on the predicted flow stress and in-plane strain ratio for the uniaxial and biaxial tensions. In the cross loading, the latent hardening coefficient of 1.4 increases the flow stresses, which is higher than the experimental data. Incorporation of the back stress reduces the reyield stress in the reverse loading. It also decreases the reyield stress in the cross loading.
This study was conducted to reveal the relationship between the α2 phase morphology and the mechanical properties of Ti-48Al-2Cr-2Nb fabricated by electron beam melting (EBM). Tensile and creep tests were conducted for three kinds of samples: an as-HIP (hot isostatic pressing) sample and samples heat-treated at 1300°C and 1400°C after HIP. The microstructure observation in the as-HIP sample showed duplex-like structure/γ band layers formed by the EBM process. The HIP-1300 sample consisted of γ single grains, blocky α2 phase grains, and α2/γ lamellar grains with decomposed α2 lamellas. The tensile properties and creep resistance of the HIP-1300 sample were inferior to those of the as-HIP sample because the α2/γ interfaces of the blocky α2 phase were incoherent. The HIP-1400 sample, which had fully lamellar structure, was fractured in the elastic region, although this sampleʼs creep resistance and life were superior to those of the other samples due to the lamellar interfaces, coarse grains, and zig-zag grain boundaries.