Materials Science Forum Vols. 551-552

Abstract: General Motors has developed Quick Plastic Forming (QPF) as a hot blow forming process capable of producing aluminum closure panels at high volumes. This technology has been successfully implemented for automotive liftgates and decklids with complex shapes. This talk will review key elements of the QPF process, describe some of the technical achievements realized in this process, and identify areas for future research in process, material, and lubricant development.

Abstract: The ultrafine-grained (UFG) 1421 aluminum alloy processed by equal channel angular pressing (ECAP) has demonstrated enhanced superplasticity at low temperature and high strain rates. This UFG material was successfully rolled at temperatures of 330-370oC retaining small grain size and equiaxed grain structure. The microstructure of the UFG alloy subjected to warm rolling (WR) was studied, and the mechanical properties of the ECAP+WR samples with UFG structures were investigated. We have found that the rolled material exhibited not only the enhanced superplasticity, but also high strength at room temperature.

Abstract: The availability to produce Ti-6Al-4V sheet material with submicron-grained microstructure for superplastic forming (SPF) has been studied. The laboratory scale sheets with an average grain size of 0.3 μm and the commercial size sheets with an average grain size of 0.65 μm were produced by pack rolling manufacturing technique from the forgings with pre-formed submicrocrystalline (SMC) structure. The sheets possessing isotropic mechanical properties in the sheet plane had higher yield strength, ultimate tensile strength. Over the exceptionally low temperature range of 700-750°C the SMC sheets demonstrated enhanced superplastic properties, namely an initial flow stress of 20-25 MPa and elongation more than 600% at the strain rate of 3×10-4/s. The sheet material with SMC structure was characterized by well formability compared to a conventional sheet under low temperature superplastic conditions.

Abstract: Today heat resistant cast steels are the nominal solution for Ti-SPF forming die manufacturing. Nevertheless, this materials present some drawbacks related to delivery time and cost. A fibre reinforced refractory castable (FRRC) is proposed as a new solution for prototype SPF die manufacturing. Due to the general brittleness of refractory castables, a short fibre reinforcement has been investigated in order to avoid catastrophic failure during the forming process. General macroscopic behavior of such materials is very complex and presents large evolutions with the testing temperature. The paper addresses the important benefits of the reinforcement for refractory castable in the case of loading on a complex structure. The capability of the material to support several cracks is shown in the case of a technological sample with a complex shape.

Abstract: Institute of Space and Astronautical Science (ISAS/JAXA) in collaboration with Mitsubishi Heavy Industries (MHI) has developed fuel and gas tanks for reaction control system and orbital control system of satellites; A tank is fabricated through welding of two thin, hemi-spherical or conical parts, which are fabricated by superplastic blow forming. Mass-productivity is not an important factor but the forming precision and flexibiliry in the process are important for this application. ISAS and MHI, therefore, developed a new blow-forming technique, which has high flexibility in terms of tank size because it requires a furnace but not a hot-press machine. Some typical propulsion tanks fabricated through this process are presented.

Abstract: Superplastic forming and diffusion bonding (SPF/DB) processes have been growing mature and titanium SPF/DB components have found wide application in aerospace industry. With the development of industrial SPF/DB technology, the size of SPF/DB components become bigger and bigger, and the shapes of components become more complex. However, the component sizes are limited by equipments, dies and the size of sheet. SPF/DB combined with welding technologies could be one of the possible solutions to form larger and more integrated structures due to many advantages compared with conventional process. This paper studied the combination processing of SPF and other welding methods besides diffusion bonding, such as electron beam welding and laser beam welding, and explained the experiments performed in different processes, including SPF after welding plate and welding plate after SPF. The results show that the material exhibits both reasonable formability and excellent mechanical properties. Application samples such as covers were manufactured by the combination processing. Furthermore, prospects of the combining technology were discussed at the end of paper.

Abstract: Grain refinement and high temperature deformation in two kinds of magnesium alloys subjected to friction stir processing (FSP) have been investigated. One was a rolled sheet of LA141Mg and another was a cast plate of AZ91Mg. FSP was developed by adapting the concepts of friction stir welding to obtain a fine grain size in a stirred zone. Grain refinement was achieved by FSP to give fine grain sizes of 11.4μm and 8.4μm for LA141 and AZ91 alloys, respectively. For LA141 alloy, the maximum stress of the FSPed sample was higher than that of the as-received one in the range of 300K to 523K while the elongation to failure of the former was considerably smaller than that of the latter. On the other hand, the elongation for the FSPed sample of AZ91Mg showed three times larger elongation with a lower maximum stress than the as-received cast one at 523K and 2.8×10-3s-1. Further difference in high temperature deformation for both magnesium alloys was discussed based on microstructural change and stress-strain curves.

Abstract: Friction Stir Welding (FSW) for aviation and automobile applications has been investigated at Osaka East Urban Area Industry-Government-Academia Collaboration Project on FSW sponsored by a Japanese ministry of education, culture, sports, science and technology, 2004-2007. The objective of this project is the three dimensional (3D) FSW of light metallic materials. The project consists of two simultaneous investigations. One is the approach from material side. The establishment of optimum FSW conditions and the construction of the FSW equation between weld condition and formed microstructure. The other is the approach from 3D software. The construction of optimum algorism for 3D FSW is the main theme. The construction of 3D FSW expert system for aluminum alloys, magnesium alloys and titanium alloys is the goal of us in combination of the results developed by the two research group.