Materials Science Forum Vols. 561-565

Abstract: Changes in the mechanical properties on AZ91 Mg alloy cast into sand mold caused by heat-treatment and its microstructure were investigated by the tensile test and observation using optical and scanning electron microscopes, and chemical composition analysis. Tensile test results show that the specimens aged at 441K have larger elongation than those of aged at 489K, although they had same proof stress. The fracture surface observation reveal the cleavage fracture of aged specimen caused by the nodular structure as well as the formation of micro void around the coarse spheroidal Al-Mn-(Fe) phase.

Abstract: Statistical continuum approach is used to predict effective conductivity of anisotropic random porous heterogeneous media using two-point correlation functions. Probability functions play a critical role in describing the statistical distribution of different constituents in a heterogeneous media. In this study a 3-dimensional two-point correlation function is utilized to characterize the anisotropic porous media of a Cathode materials to incorporate all the details of the microstructure. These correlation functions are then linked to the effective properties using homogenization relations. An anisotropioc Green’s function solution is used to solve the set of field equations. Examples in this study demonstrated how the model captured the anisotropy in effective conductivity of the random heterogeneous media. Predicted results showed the influence of microstructure on the effective conductivity tensor.

Abstract: Aluminum alloys 6061-T6, 7075-T6 and 7249-T76 were subjected to several combinations of solution treatments, quenching media, and age hardening treatments to correlate their mechanical tensile properties to hardness and conductivity measurements. Additionally, the 6061-T6 and 7075- T6 alloys were thermally exposed to several temperatures to simulate heat damage effects. The thermal exposure was correlated to the tensile properties and hardness and conductivity measurements.

Abstract: In order to investigate the effect of the as-cast microstructure on the hot working behavior of an AZ31 magnesium alloy, specimens were cast in copper moulds with and without water cooling. A series of compression tests were performed at a temperature of 350 °C, a strain rate of 0.01 s-1, and at strains up to 1.0. It was found that as-cast microstructure is very sensitive to the solidification conditions, which leads to a significant difference in flow behavior and dynamic recrystallization (DRX) characteristics. It appears that more uniform and refined as-cast grain size promotes dynamic recrystallization and reduces the flow stress. It is also possible that second phases (>1+m in size) contribute to DRX by acting as nuclei.

Abstract: Al-Ti-C master alloy with or without the TiH2 was prepared by Self-propagating High-temperature Synthesis (SHS) induced by laser. The phases, composition, microstructure morphologies of master alloy and its thermal reaction process were investigated by XRD, EPMA, DTA and SEM. The results show that adding TiH2 has obvious effect in promoting the synthesizing reaction of Al-Ti-C master alloys. Active Ti atoms and catalyzing H atoms released by TiH2 thermal decomposition cause critical reacting temperature of the SHS decreasing. The addition of TiH2 affects the morphologies and distribution of TiAl3 and TiC particles (size of TiC was smaller than 1μm in diameter), and restrains the congregating tendency of TiC particles. The refining test on aluminum indicates that master alloys with TiH2 possesses more excellent grain refining perfprmance than without, because of the composition and morphology of the master alloy is cut out for refining processing.

Abstract: Binary Mg-Al alloys with varying content of aluminium from 0.5 to 12mass% have been studied. The proof stress increase in two steps whereas the ductility exhibits two correlated stepwise drops, as the aluminium content increases. The first increase in strength, and attendant drop in ductility, is observed between 4 and 5 mass% Al. The second stepwise change is observed between 10 and 12 mass% Al. These effects are connected with well defined changes in the microstructure: at 4 mass% a dispersion of β-phase intermetallic particles appears in the core region and a closed cell structure develops near the surface; at 12 mass% Al, the increased volume fraction of the β- phase intermetallics extends the interconnected network of intermetallics to include the core region as well. The micromechanics of the strengthening and decreased ductility are discussed.

Abstract: Al-Si alloy was melted by using vacuum induction melting furnace heated with medium-frequency induction and stirred simultaneously under Lorentz force. The experimental results were discussed with respect to the theoretical analysis of the Lorentz force on the molten alloy. It was found that Si phase tends to homogenize and aggregate along the direction of axis in the alloy under the effect of Lorentz force. With increasing stirring duration, Rod-shaped Si phase has a tendency to break and passivate on the edge. Vickers hardness measurement indicated that the microhardness of Al-Si alloy was improved after electromagnetic stirring. This result can be mainly attributed to the improvement in spheroidization of Si phase and aluminum phase.

Abstract: The presence of surface defects, such as streaking, is one of the most serious quality issues for 6000-series aluminium extrusions. The formation of a streaking defect near a web intersection of a hollow profile was investigated in detail. The streak was apparent on the extrusion in both the as-extruded and the as-anodised conditions. Microstructural examinations indicate that the streaked region contains different surface imperfections compared to the normal region and smaller grains and stronger texture than the normal region. The effects of die design and microstructural variables on the formation of streaks on aluminium extrusions are discussed.

Abstract: The transformation of Bocar Automotive Products from an aluminium products fabricator to an innovative manufacturer supplying automakers with accessory product systems has required the adaptation of forming processes and product capabilities to address the relatively small volumes in the Australian market, strategic change in the company’s target markets and cultural change in its internal operations. The strategy for developing new capability in the casting and forming of aluminium alloy products has taken place over 5 years beginning with the bending of extruded shapes, progressing into the forming of sheet aluminium alloys and the casting of bumper bar components, and finally into the integration of these processes into bumper systems for a number of 4 Wheel Drive models. This paper describes the product design, metal forming and production changes that Bocar has introduced and integrated with its marketing strategy to become a recognized innovator in the accessories market in Australia.