Materials Science Forum Vols. 519-521

Abstract: A novel method is introduced to investigate the macro-segregation in 356 Al-Si alloy. In this method, a portion of the remaining liquid is extracted during solidification of the alloy from the bottom orifice of a cylindrical sample. Different parts of the sample plus the extracted material are chemically analyzed and a good correlation between the chemical composition and the predicted values from binary Al-Si diagram was obtained. Comparing the chemical composition of the decanted alloy in the cast piece with those of the 356 standard range has shown that even with 15% of the liquid extraction, the composition of the alloy is still within the intended range.

Abstract: A novel process named Controlled Diffusion Solidification (CDS) has been developed to circumvent problems that are typically associated with casting wrought aluminum alloy compositions into near net shaped components. The process involves bringing two precursor alloys of precisely controlled composition, temperature, and quantity into intimate contact, and then casting the resultant alloy using a conventional casting process to yield a component of predetermined composition with a microstructure that is similar to that of semi-solid processed alloys. Describing the many interactions that occur during solidification of aluminum alloys in a consistent manner is virtually impossible without the use of computational tools that are based on thermodynamic models. In this paper, we describe how the CALPHAD method, which allows calculating all the necessary data from thermodynamic model parameters, was used along with theoretical calculations and empirical rules to allow describing the Gibbs free energy of each phase in the alloy system and yield quantitative data that guided the development and optimization of the CDS method.

Abstract: Models describing the critical steps in the manufacturing process of aluminum alloy wheels were integrated with a model of in-service loading to predict component fatigue performance. A multiscale solidification model was coupled with models of the subsequent heat treatment and machining to predict the residual stress distribution in a finished wheel. A second multiscale model was incorporated into a service model to relate the pore size and local stress state to fatigue performance. The predictions resulting from this through process modeling approach have been validated by comparisons with a series of measurements: 1) thermocouple measurements during casting; 2) characterization of pore size and distribution using X-ray microtomography and optical metallography; 3) residual strain measurements on finished wheels; 4) in-service strain measurements during a rotating bend test; and 5) in-service fatigue performance during rotating bend tests.

Abstract: This paper contains a review of microstructural through-process modelling (TPM) and the particular role of ingot metallurgy from an industrial perspective, focusing on recent advances in solidification theory, solidification and homogenisation software, and software environments that allow models to interface. To illustrate how as-cast microstructure can impact on downstream processing steps, a sensitivity analysis has been performed on an AA1xxx alloy using an in-house homogenisation model. Thus, knowledge gaps in theory and model application are highlighted.

Abstract: Effects of solidification range on macro- and microstructure of pure aluminium and binary Al–Cu alloys obtained under conditions of constant melt flow are studied experimentally. The solidification range of binary alloys was varied by changing the concentration of the alloying element. An electromagnetic pump with a specially designed melt-guiding system is used to organize controlled unidirectional melt flow along the solidification front. Temperature and melt flow velocity are controlled during the experiment. It is observed that the extent of solidification range changes the macro– and microstructure, affects width and deflection angle of columnar grains, and alters the dendrite arm spacing in the presence of melt flow. The melt flow itself is found to change the macro- and microstructure, e.g. the increase of melt flow velocity clearly decreases the dendrite arm spacing.

Abstract: Technical Al-Si alloys always contain sufficient amounts of Fe and Mn, especially alloys made from scrap. During casting, Fe-containing intermetallics, such as Al-Fe, Al-Fe-Si and Al-Fe- Mn-Si phases, are formed between the aluminum dendrites. Fe and Mn-rich intermetallic phases are well known to be strongly influential on mechanical properties in Al-Si alloys. In the present work the influence of controlled fluid flow conditions on the morphology and spatial arrangement on intermetallic phases in cast Al-Si alloys is characterized. A binary Al-7wt.%Si and a ternary Al- 7wt.%Si-1wt.%Fe alloy was solidified under and without the influence of a rotating magnetic field (3mT at 50Hz) over a range of solidification velocities (0.015- 0.18mm/s) at a constant temperature gradient G of 3K/mm. The scientific results reached so far indicate a strong influence of the electromagnetic stirring on the primary dendrite and secondary dendrite arm spacings.

Abstract: The economical and environmental effects of mass reduction through Al and Mg primary alloys substitutions for cast iron and steel in automotive components are discussed using M.F. Ashby’s penalty functions method. The viability of Mg alloy substitutions for existing Al alloy cast components is also considered. The cost analysis shows that direct, equal-volume, Al alloy substitutions for cast iron and steel are the most feasible in terms of the CAFE liability, followed by substitutions involving flat panels of prescribed stiffness. When the creation of CO2 associated to the production of Al and Mg is considered, the potential gasoline savings over the lifespan of the car compensate for the intrinsic environmental burden of Al in all applications, while electrolytic Mg substitutions for cast iron and steel are feasible for equal volume and panels only. Magnesium produced by the Pidgeon thermal process appears to be too primary energy intensive to be competitive in structural applications. Magnesium substitutions for existing Al alloy beams and panels are generally unviable. The current higher recycling efficiency of Al casting alloys confers Al a significant advantage over Mg alloys.

Abstract: Novelis Inc. recently released its first new innovative technology which opens new opportunities in the clad aluminum product marketplace, where a combination of mechanical and physical properties can be obtained which are superior to the monolithic material alone. Clad aerospace and brazing products are well known commercial products which are provided by commercial roll bonding processes, but which can now be produced with the new Novelis technology. This paper discusses the new technology, e.g., the casting, fabrication, the properties of clad sheet are reported and it is established that the clad-core interface is comprised of a high strength, oxide free zone. This technology enables a new family of clad products with clad/core combinations which cannot be produced by the conventional roll bonding process.

Abstract: Structural states of Al-Sc, Al-Hf and Al-Zr alloys rapidly quenched from the liquid state have been studied. Features of structures in dependence on the nature of alloying elements, on the quenching temperature and the cooling rate by the crystallization of ribbons have been investigated. Fractal structures are formed by the quenching from the certain temperature-concentration region. The change of the morphology of structures has been researched during the aging process.

Abstract: Closed-loop recycling should be promoted for wrought aluminum alloy scraps including impurity iron in order to use natural resources effectively. Fabrication of the alloy strip using a high rate of cooling is a promising method for reducing the detrimental effects of impurity iron. In the present study, strips of A6022 aluminum alloy with various Fe contents of up to 1.5 mass% were fabricated by a vertical-type, high-speed, twin-roll caster. The caster used in the study was equipped with a pair of water-cooled, pure copper rolls, and a cooling slope upstream of the rolls. The strips exhibited a common microstructural feature. Columnar grains grew from both surfaces of the strip, and they were gradually replaced by equiaxed grains. In the mid-central region, a band of fine grains was observed. Such fine grains seemed to originate from the crystallized α-Al dendrites on the cooling slope or the roll surfaces. Internal cracks were observed in the A6022 alloy strip that was subjected to the highest cooling rate. The cracks were located between equiaxed grains and fine grains at the mid-central region. The cracks were reduced with increasing Fe content. No cracks were observed for the alloy strips with 1.0 mass% Fe or greater. It was found that both a slight reduction in the cooling rate and addition of Fe were effective for obtaining sound A6022 strips.