2011 年 52 巻 2 号 p. 173-178
Bulk nanostructure of commercially available aluminum alloy of AA6061 was made by an equal channel angular extrusion (ECAE). The effect of the ECAE routes of A, Bc and C on change of microstructure was investigated up to four passes by using the split die set-up. Formability of the ultra-fine grained specimens processed by the ECAE was measured by a compression test. In this test, the specimen made of the conventional material did not buckle when the aspect ratio of the height to the diameter (4 mm) of the specimen was 2.1 but the ultra-fine grained specimens with the same aspect ratio buckled. Considering the limiting value of the aspect ratio obtained from the compression test, a bolt forming sequence was developed into three stages. Load requirement and possible defect formation during the forming process were predicted by employing a rigid-viscoplastic finite element analysis. After manufacturing the high strength bolts using the ultra-fine grained specimens, strength increase was confirmed by the tension test and transmission electron microscopy. Homogeneity of strength increase was also examined by measuring local hardness distribution. In addition, the manufactured bolt with the ultra-fine grained AA6061 was compared to the one manufactured with commercially available AA2024 in terms of strength increase and its homogeneity. According to the present investigation, an innovative approach to utilize the ECAE to manufacture the high strength bolt using the conventional material without applying additional alloying elements or heat treatment is demonstrated.
