Materials Science Forum Vols. 794-796

Abstract: A new experimental technique, which is based on a kinetic model of particle transport, has been proposed for determination of the capture efficiency of particles by bubble flotation. Cold model experiments by using an aqueous solution and plastic particles are carried out to validate the new experimental technique. Plastic particles having poor wettability tend to adhere to bubbles and they are removed from an aqueous solution by bubble flotation. On the other hand, plastic particles good in wettability are not captured by bubbles. Capture efficiency can be estimated from a difference of transfer rate between the particles having poor and good wettability. The capture efficiency is found to be proportional to the size ratio of particle and bubble, d_p/d_b, and agrees with theoretical results of Sutherland (1948) for a potential flow condition.

Abstract: During remelting of aluminum manganese-containing alloys, some industrial experience has indicateda tendency toward increased oxidation losses when compared to unalloyed Al. A goal of thiswork is to increase current knowledge of oxidation of Mn-containing aluminum. An oxidation studywas performed on 99.99% Al, Al-1%Mn and Al-5%Mn materials in a muffle furnace in air. Theseoxidized materials were analyzed in the Scanning Electron Microscope using Energy Dispersive xraySpectroscopy (EDS) both for chemical composition and to analyze the structure of the oxide thatwas formed. The main findings from the SEM analysis of the oxidized 99.99% Al, Al1%Mn andAl5%Mn materials are: 1) The oxides formed on the Al1Mn and Al5Mn materials contained onlyminute amounts of Mn. However, small clusters of Mn metal were found among the Al2O3 particleson the surface of the Al1Mn and Al5Mn samples. 2) Dissolved Mn increased from the surface to theinterior, and Mn-rich particles were present in the interior of the Al1Mn and Al5Mn samples. 3) Theoxide layer thickness increases with Mn content, and the oxide film is more fragmented.

Abstract: The heat exchanger market requires aluminum brazing sheet that offers a good balance of properties, namely: corrosion resistance, brazability, and post braze strength. A new long life brazing sheet alloy which has attractive properties in the post braze condition has been developed. Specifically, higher post braze strength and improved air side corrosion resistance has been obtained. In addition, a deeper understanding of dense precipitate band (DPB) formation in higher Si containing core alloys during brazing has been developed. The new alloy will lead to improvements in radiator tube stock performance.

Abstract: Microstructures and mechanical properties of the D-SSF (Deformation Semisolid Forming) processed Al-Zn-Mg alloys with high Fe content up to 2 mass% were investigated. A high ductility alloy even containing 1 mass% Fe was successfully produced by applying the D-SSF process. Especially, the D-SSF processed alloy with 1 mass% Fe was superior to the conventionally processed alloy with Fe-free in the properties of the tensile strength and elongation. These results clearly indicate that the harmful influence by the addition of 1 mass% Fe is effectively modified into not harmful one by applying the D-SSF process. Furthermore, the former liquid phase regions (FLP regions) which are finally solidified during the D-SSF process are completely extinguished by the solution treatment and resultantly the mechanical properties are greatly improved. The extinction process of the FLP regions during the solution treatment was examined using an EBSD method in terms of the crystal orientations of the α-Al grains.

Abstract: Twin roll casting (TRC) has been demonstrated to be an effective route for producing Al sheet at a reduced cost. However, the quality of the Al alloys sheets produced by the TRC process is limited by the formation of centreline segregation, which hampers the downstream processing, degrade the mechanical performance of the final rolled products, limit TRC to dilute alloys with a narrow freezing range, and hence prevent its application in a wide range of engineering sectors. To improve the quality of the TRC strips, a new technology, melt conditioning twin roll casting (MC-TRC) has been developed. It has been demonstrated that the MC-TRC process is capable of producing Al-alloy strips with minimal centerline segregation which is attributed to enhanced nucleation by well dispersed naturally occurring oxides in liquid Al alloys. This work aims to investigate the upper composition limit allowed for the MC-TRC process using the binary Al-Mg alloys as model alloys. The results showed that melt conditioning increases the range of alloys (solute content up to 7%) that can be twin roll cast without severe segregation.

Abstract: The effect of different thermomechanical processes (hot extrusion and Properzi continuous rolling) on the electrical and mechanical properties of the Al-Fe aluminum conductor alloys was investigated. The microstructural evolution of the supply rods was characterized by an optical microscope, a transmission electron microscope and the electron backscatter diffraction technique (EBSD). Tensile tests and electrical conductivity measurements were carried out at room temperature on the supply rods. Results showed that, at the same Fe content, the continuously rolled rods demonstrated higher tensile strength but lower elongation and electrical conductivity compared with those of the extruded rods. A partially recrystallized structure along with a big subgrain size appeared in the extruded rods while only a dynamic recovery with a small subgrain size was found in the continuously rolled rods. The precipitation of iron-rich dispersoids was observed in the extruded rods and is associated with a depletion of the iron concentration.

Abstract: Two different conditions were used to study the effect of homogenization on extrusion texture and microstructure evolution in AA3003. The first condition considered homogenization for 8 h at 500°C to obtain a high density of dispersoids and the other condition was homogenized for 24 h at 600°C to produce a sample with a very low density of dispersoids. After uniaxial extrusion at 400°C with a speed of 32 mm/s and an extrusion ratio of 70:1, the material with a high density of dispersoids formed <001> and <111> double fibre texture in the centre of extrusion rod and a smeared texture from <011> to <111> near the surface. For the material without dispersoids, only <001> texture fibre is observed in the centre of extrusion rod and a strong <011> fibre is observed near the surface.

Abstract: Dynamic interactions between plastic deformation and precipitation processes in Aluminium alloys can lead to large changes in precipitation kinetics as compared to conventional heat treatments. This can be due to a number of different mechanisms such as changes in vacancy concentrations or movement of structural defects. Understanding the underlying mechanisms requires a quantitative measurement of the precipitate evolution as a function of deformation conditions, temperature and time. The present contribution will review experimental results obtained by Small-Angle X-ray Scattering in three different configurations, all concerning Al-Zn-Mg-Cu alloys: first, dynamic precipitate evolution during plastic deformation at ageing temperature; second, dynamic precipitation during low cycle fatigue at room temperature; and third, precipitation during ageing of a material processed by room temperature high pressure torsion. The experimental evidence will be used to discuss the role of the different mechanisms of interaction with plasticity on the precipitate microstructure evolution.

Abstract: In order to improve formability, it is practicable to control the texture through adjusting process parameters. This work describes the evolution of microstructure and texture during thermomechanical processing of Al-Mg-Si-Cu alloy. With the change of deformation conditions, both the microstructure and texture change dramatically. After hot rolling from 90 mm to 7.5 mm, H and E texture components in the surface layer become dominant due to non-uniform deformation. And then with the increasing of cold rolling deformation from 7.5 mm to 4.0 mm, the texture components gradually change from shear texture to typical fcc texture, i.e. Copper, S and Brass textures, and their intensities also increase. And these texture components transform to some uncommon texture components after intermediate annealing, including {013}<001>, {001}<130>, Goss texture, {556}<110> and {111}<110> texture, not as the typical recrystallization texture components. Continually giving a cold rolling deformation from 4.0 mm to 1.0 mm, not only Copper, S, Brass textures, but also Goss texture due to the lower deformation can be found in the alloy sheet. The high temperature solid solution treatment can result in the complete recrystallization and the formation of recrystallization texture, Cube, Goss and R texture, which results in the high formability of experimental alloy.

Abstract: The effect of Manganese as alloying element and important process parameters on the microstructure of AA 8006-alloys was investigated in this work. Furthermore the effect of different casting processes (CC-casting versus DC-casting) was studied. The addition of higher Mn-contents results in higher strength values and a better thermal stability. The recovery and recrystallisation behaviour is also influenced by the processing. Important process steps are the preheating and the intermediate annealing. The properties at final thickness are also related to the applied casting process ( DC versus CC).