Materials Science Forum Vols. 638-642

Abstract: Microstructure and hot workability have been considered for a number of -TiAl alloys including -solidifying TNM alloys. All TNM alloys under study showed improved hot workability in cast condition. As was shown for the Ti-45Al-5Nb-1Mo-0.2B alloy, a critical issue of TNM alloys is room temperature ductility in the conditions with lamellar structure.

Abstract: Aluminum alloys are commonly used as a material for heat exchangers due to their higher thermal conductivity and specific strength among various metallic materials. The lightweightening heat exchangers for automobile application are requisite for reducing the evolution of CO2 and improving the efficiency of fuel. The twin roll strip casting process is considered to produce the high quality and low manufacturing cost aluminum alloy fin stock for automobile heat exchangers. Thermomechamical treatment has carried out to obtain optimum processes for initial cold rolling, intermediate annealing and final cold rolling, which can meet the requirements for high strength and high thermal conductivity after brazing heat treatment. Mechanical properties and thermal condutivity have been evaluated before and after simulated brazing process. The nuclei of recrystallization might be formed along shear deformation bands during initial cold rolling and should be grown during intermediate annealing to enhance the permeation of molten brazings for the following brazing process. Final cold rolling has allowed strain hardening and controlling of sagging amount as fin stock materials of heat exchanger. In the present study the suitable thermomechnical treatment was suggested to balance the properties of strength, thermal conductivity, brazing behavior and sagging in Al-Fe-Mn-Si-Zn based alloys produced by twin roll strip casting process.

Abstract: The industrial production of aluminium strip comprises a rather long process chain. One of the characteristics of aluminium alloys is that a number of final strip properties are influenced considerably already at very early process stages. Since it is practically impossible to run large variations of controlled process changes on an industrial mill experimentally, Through Process Modelling (TPM) has been in focus of research and has developed into a valuable tool to design process chains with a view to achieving desired properties. Metallurgical models in combination with (plasto-) mechanical/thermal models trace variables of state through the process chain down to the final operation. However, there are further important properties of the product, which may be generated as consequence of the total production history. Predominant examples are the strip profile and flatness and the product surface. These properties do not only result from the processes settings, they may also have a strong back-effect on the process performance itself. As a consequence they may also affect the metallurgical properties. This paper shows representative computations of in-dustrial aluminium rolling process steps to evaluate the interactions of different mechanisms taking place in the rolling processing chain, with a special attention to profile/flatness, surface and metal-lurgical properties.

Abstract: Since the Continuous Casting & Rolling of the non-ferrous metal by Illario Properzi have invented in 1944, the various non-ferrous rod, wire and sheet are produced at present. Although there is long research and trials for producing the wire or rod of commercial the high-strength aluminum alloy, there are few companies with the success in producing commercial hard-aluminum alloys wire and rod by CC&R process. The application of the high-strength aluminum alloy rod or wire is various parts such as rivet, bolt, sports leisure supplies, high-tension power transmission wire, machinable and forgeable materials. However, it is very difficult to produce the high-strength aluminum alloy wire and rod by CC&R process because of the wide mushy zone and high strength compared with the pure or low strength aluminum alloy. Additionally, it is easy to crack and breakout in casting and rolling process due to tiny internal defects of the castings. The object of this project is to design the most suitable equipments for CC&R and optimize the experimental condition of continuous casting condition of the high-strength aluminum alloy. The facilities of CC&R process in RIST are composed of the melting furnace, the wheel casting machine, the automatic machine for moving of castings bar, the 15-step rolling machine with three rolls, the induction heater for reheating the castings bar and the coiling machine. In the present work, through the numerical computer simulation, in first, we have developed the thermal model of the solidification behavior of the casting bar. Finally, using finite element code, Marc, the temperature distribution of each rolled bar and effective strain are obtained during continuous rolling.

Abstract: In order to investigate the effect of deformation on the aging response of Al-Mg-Si alloys, a series of tensile tests have been designed and carried out on two commercial aluminium alloys, i.e. AA6060 and AA6082. Extruded and solution heat treated specimens were pre-deformed 0%, 5%, and 10% (engineering strain), respectively followed by natural aging (NA). It was observed that the work-hardening rate increases with prolonged natural aging time and decreases with increasing pre-deformation prior to natural aging. The most significant effect of deformation was obtained for T4 temper i.e. after 1000 and 10000 minutes NA for the 6082 and 6060 alloy, respectively, when the amount of pre-deformation is 10%. A remarkable difference in work-hardening rate at the level of small plastic strains was observed compared to that of the material naturally aged for only 10 minutes. In addition to the tensile tests, transmission electron microscopy (TEM) has been used to characterize dislocation evolution for various combinations of pre-deformation and aging time.

Abstract: Excessive iron in aluminum melt produces needle-shaped beta-AlFeSi intermetallic compounds during solidification. The presence of beta-AlFeSi intermetallic compounds can be harmful in the extrusion process because of the high pressure. As a common process, those compounds change from the needle-shaped to the globular-shaped alpha-AlFeMnSi intermetallic compounds through the addition of manganese to the aluminum melt. Those phases settle down during the solidification process, and then such is cut. Note, however, that the efficiency of iron elimination is very low. Our previous study reported that EMS can help the alpha-AlFeMnSi intermetallic compounds form easier and faster and settle down at the bottom of the aluminum melt through the centrifugal force of EMS. To investigate the effect on the efficiency of iron elimination in aluminum melt scrap, EMS current, holding temperature, and time of melt as well as the ratio of manganese to iron were controlled. As a result of this study, lower holding temperature and longer holding time of aluminum melt make iron elimination in aluminum melt more efficient with induced EMS. The best efficiency of iron elimination in aluminum melt was 65.2%with EMS induced at 923k for 4 minutes.

Abstract: In this study, the effect of various aging treatment (T6 and T7 treatment) on the mechanical properties, electrical conductivity and the microstructure of an Al-7.5Zn-1.3Mg-1.4Cu-0.12Zr alloy has been investigated. The results show that with elevating the aging treatment temperatures, the aging response rate is greatly accelerated. When T6 temper is performed at 140°C for 12h, as compared to peak aging for 24h at 120°C, the UTS and the corresponding Elongation values keep the same level, whereas the TYS and the electrical conductivity obviously increase by 5% and 9%, which is up to 560 MPa and 22.6 MS/m, respectively. And there are clear PFZs along the grain boundary and slightly coarser precipitates inside the grain. GPI zones, GPII zones and η' phases are major precipitates for the alloy under T6 condition. When T7 temper is performed on the alloy, the main precipitates are GPII zones, η′ and η phases. The coarser precipitates inside the grain and discontinuous grain boundary precipitates are favorable to electrical conductivity, which decrease the strength of 5~17% compared to T6 treatment. After T76 treatment (i.e., 110°C/6 h + 160°C/6 h), the UTS, TYS, Elongation and electrical conductivity values were 540 MPa, 510 MPa, 16.7% and 23.5 MS/m, respectively.

Abstract: The particle morphology and composition of nanometer-scale Al3(Zr1-xTix) precipitates formed after aging at 450 °C for 1 h in Al-0.3mol%Zr-0.5mol%Ti alloy were investigated using high resolution electron microscopy (HREM) and three dimensional atom probe tomography (3D-APT). The alloy exhibits an inhomogeneous distribution of solute atoms after casting. After aging, Al3(Zr1-xTix) precipitates with a metastable L12 structure formed within solute-enriched dendrites. The Al3(Zr1-xTix) precipitate particles were spherical with diameters between 3 and 5 nm. The Al3(Zr1-xTix) precipitates were found to be coherent with matrix using HREM. Interfacial segregation of Ti at the matrix/precipitates was also observed in the composite Al3(Zr1-xTix) precipitates. The Zr:Ti atomic ratio in the Al3(Zr1-xTix) precipitates measured by 3D-APT was approximately 7 (x=0.125).

Abstract: A recent work hardening model developed by Nes and co-workers at NTNU, Trondheim provides a unified theory for warm and cold stress-strain behaviour which in principle accounts for alloy aspects such as effect of dispersoids (size and number density) and solute content, including dynamic strain aging for Mg containing aluminium alloys. In the present paper the applicability and predictive power of the model are tested for multicomponent alloys to account for the combined effect of different solute elements in solid solution and dispersoids, with a special focus on hot deformation of a range of Al-Mg-Mn alloys. It is demonstrated that the model, without any re-tuning, only accounting for the variations in alloy chemistry and deformation conditions is capable of predicting the stress-strain for a range of compositions, strain rates and temperatures.

Abstract: Superplasticity in an Al-6%Cu-0.45%Mg-0.4%Mn-0.16%Sc-0.12%Zr alloy subjected to intense plastic straining through equal-channel angular extrusion (ECAE) was studied in tension at strain rates ranging from 5.6×10-4 to 5.6×10-3 s-1 in the temperature interval 350-450°C. The alloy had a non-uniform microstructure with an average crystallite size of 1.2 m. The volume fraction of high-angle grain boundaries was about 57%. In spite of small crystallite size the alloy shows moderate superplastic properties. The highest elongation-to-failures of 320% appeared at a temperature of ~425°C and an initial strain rate of ~1.410-3 s-1, where the strain rate sensitivity coefficient, m, was about 0.33. The relationship between superplastic ductilities and microstructure stability is analyzed.