In order to investigate the effect of boron on the precipitation behavior of β phase in Al-Mn-Mg-B alloy used as a material for cask baskets, 1.00×10⁴ hours aging treatment was carried out focusing on the temperature history in the cask as in the previous report, and the Time-temperature-precipitation diagram and Supersaturation-diffusion length-precipitation diagram were evaluated using the change tendency of the specific resistance obtained. In the Al-Mn-Mg-B alloy, although grain refinement by AlB₂ was confirmed, the effect of boron addition on the precipitation rate of β phase was hardly recognized. That is to say, it was confirmed that the grain boundary and the interface between B compound and matrix phase hardly contributed as nucleation sites of β phase. In conclusion, it is considered that the reduction of the solid solution Mg content in the Al-Mn-Mg-B alloy does not occur even after 60 years if the Mg content is 1.0 mass% as in the Al-Mn-Mg alloy.

This study investigates the applicability of the forming limit strain (FLS) and fracture limit strain (FrLS) determined from uniaxial tensile tests for predicting the hole expansion limit of a 6000-series aluminum alloy sheet. Since the stress state at the hole edge in hole expansion is uniaxial, the FLSs and FrLSs of the test sample are determined from the uniaxial tensile tests at various cut angles from the rolling direction. The experimental methods for determining the FLS and FrLS are presented. In the hole expansion experiment, the development of the strain distribution at a position 3 mm apart from the hole edge was precisely measured using digital image correlation method for three different hole diameters, and the maximum principal strain along the hole edge, ε₁, was compared with the FLS and FrLS. We have confirmed that the fracture in the hole expansion experiment always occurred at the hole edge and when ε₁ reached the FrLS, regardless of the hole diameter. Therefore, the FrLS can be a criterion for predicting the hole expansion limit of the test sample.

Magnesium is a metal material with both bioabsorbability and biocompatibility, and the fine wire is expected to be applied to bioabsorbable implants. It is desirable that the alloy composition is composed only of bioessential elements such as calcium and zinc, and the composition does not form the second phase precipitate of unknown biological toxicity. However, there are few studies on magnesium fine wires, and their degradability. In the case of surgical clips, staples, sutures, etc., it is necessary to consider bending deformation during ligation. In this study, fine wires of Mg-0.3 mol%Ca and Mg-0.3 mol%Zn were fabricated, and the coil was formed by the winding tester to evaluate the bending deformation. As a result, it was confirmed that Mg-0.3 mol%Zn was hard to crack, while Mg-0.3 mol%Ca was easy to crack after the deformation. In addition, an in vitro test was conducted using the prepared coil to investigate the effect of alloying elements on the degradability. After the tension bending deformation, surface appearance was inspected to know the effect of the trace alloying on the deformability. Continious observation revealed that the alloying element affect the degradability, since the shape of coil using Mg-0.3 mol%Ca and Mg-0.3 mol%Zn remained for 21 days and 35 days, respectively.