1. The Commercial Mg Alloys Tubes Hydroforming Research and Development C. C. Huang ( 黃建超 ) J. C. Huang ( 黃志青 ) N. J. Ho ( 何扭今 ) Institute of Materials and Engineering, National Sun Yat-Sen University ( 國立中山大學材料科學研究所 ) In this study used self-design piercing mandrel die, by simple one-pass forward extrusion machine, extrusion ratio is 15.4; develop AZ31 tubes of seamless and no guide hole. The operations were very easy that can save much design of die cost, and conform to industry wish-one-pass production goal. The AZ31 tubes fabricated at 250; 300; 350; 400 o C and 6x10 -3 ; 1.3 x10 -2 ; 5.4x10 -2 ; 1.1x10 0 s -1. The microstructures and mechanical properties of the AZ31 Mg tubes fabricated by one-pass forward piercing tube extrusion are examined. The experimental apparatus used for tube hydroforming is a self-designed test machine by Hwang, composing of a tube expansion set, a hydraulic power system, and a pressure intensifier, as depicted in Fig. 1. The capacity of this test machine can reach a hydro-pressure of 100~120 MPa. Abstract Results and Discussions Though the extrusion ratio was only 15.4, the resulting grain structures of AZ31 tubes are mostly recrystallized and equiaxed fine grains, measuring 2-3 µm. The grain size follows well the Hall-Petch relationship with respect to the Hv hardnesss, as presented in Fig. 4. The average room temperature UTS and elongation data on the as-extruded tubes along the extrusion direction loaded at 1x10 -3 s -1 are scattered within 289~322 MPa and 35~45%, respectively. From SEM observations, fracture plane were ductility fracture, because there were many dimples as show in Fig. 5 (a) (b). The tube is hydroformed at room temperature, therefore a brittle crack on the outer wall of the tube was observed as show in Fig. 6 (a) (b). Our parallel studies of these extrudes AZ31 Mg tubes loaded at 300-400 o C have shown reasonable superplasticity of 400-610%. Superplasticity at lower temperatures of 150-200 o C would drop to 100-275%, but appears to be sufficient for tube hydroforming. Figure 7 shows the X-ray diffraction experiment of the inner tube wall after full annealing at 400 o C for 4 h. It can be easily seen that there exists a strong {0002} basal plane texture in all specimens, independent of the preceding extrusion temperature or strain rate. All extrude tubes after full annealing exhibit an apparent and simple basal texture, with the {0002} basal plane lying parallel to the thin tube wall all over the tubes. Summary The grain size is refined from the initial ~75 µm grain size down to 2~3 µm. From results of experiments, extrusion temperatures inference more than extrusion rate for grain size of extrusion tubes. The room temperature tensile elongations of the as-extruded or fully annealed tube specimens along the 0 o, 45 o, and 90 o directions with respect to the extrusion direction are all scattered within 20-45%. Even after full annealing at 400 o C for 4 h, there still exists a strong and predominant {0002} plane texture on the tube wall. Such a texture seriously limits the room temperature tube hydroforming, due to the fact that dislocations can hardly make cross slip onto the non-basal plane to result in 3D uniform deformation. Since the basal plane texture is widely present in all rolled or extruded sheets or tubes, it is inevitably necessary to invoke forming at elevated temperatures around 200-300 o C. Otherwise, modifications of the plane texture need to be done through, for example, local friction stir processing on the critical regime requiring a higher formability limit. The grain size is refined from the initial ~75 µm grain size down to 2~3 µm. From results of experiments, extrusion temperatures inference more than extrusion rate for grain size of extrusion tubes. The room temperature tensile elongations of the as-extruded or fully annealed tube specimens along the 0 o, 45 o, and 90 o directions with respect to the extrusion direction are all scattered within 20-45%. Even after full annealing at 400 o C for 4 h, there still exists a strong and predominant {0002} plane texture on the tube wall. Such a texture seriously limits the room temperature tube hydroforming, due to the fact that dislocations can hardly make cross slip onto the non-basal plane to result in 3D uniform deformation. Since the basal plane texture is widely present in all rolled or extruded sheets or tubes, it is inevitably necessary to invoke forming at elevated temperatures around 200-300 o C. Otherwise, modifications of the plane texture need to be done through, for example, local friction stir processing on the critical regime requiring a higher formability limit.