Materials Science Forum Vols. 546-549

Abstract: Three-dimensional FEM simulations of fluid-thermal analysis of the fluid fields including the front-box and the 3C-style nozzle of aluminum roll-casting was performed by using FLOTRAN module of ANSYS. The advanced result analysis based on post-processing of ANSYS was conducted by MATLAB. According to the allowable inhomogeneity and its application of velocity and temperature at outlet, the most possible broken regions of aluminum sheets at outlet could be predicted in the case of speed increasing of the drawing-sheet and thickness reducing of the aluminium sheet during roll casting.

Abstract: Friction and wear behaviors have been studied between the untreated base material and the friction stir welds of 5052 aluminum alloy. To determine the wear mechanism surface microstructures of worn test samples were examined by scanning electron microscopy (SEM).Variation rule of wear-resistance property and coefficient of friction were investigated according to wear mass loss and moment of friction under different parameter condition. The results show that all of friction stir welds had lower coefficients of friction and higher wear resistance than base material. The abrasion loss of base material increased by six times when position pressure increased from 50N to 100N and the abrasion loss is as 10-20 times as that of friction stir welds. The value of friction-moment of friction stir welds is low and stable and abrasion principle had changed from grain abrasion to fatigue wear. Surface examination showed that adhesion and smearing was the main wear mechanism for friction stir welds.

Abstract: The deformation behavior of 2519 aluminum alloy was studied by isothermal compression by Gleeble-1500 simulator in the temperature range from 300 to 450°C under the strain rates of 0.01~10s-1. The results showed that the flow stress was controlled by strain rate and deformation temperature. The flow stress increased with strain rate and decreased with deformation temperature. The flow stress of 2519 aluminum alloy increased with strain and to the constant values at three strain rates of 0.01 s-1,0.1 s-1and1 s-1, indicating the dynamic recovery to occur. The flow stress decreased after a peak value with increase of strain at strain rate 10s-1 and deformation temperature higher than 350°C, showing partly dynamic recrystallization. The flow stress of 2519 aluminum alloy during high temperature deformation can be represented by Zener-Hollomon parameter.

Abstract: A rapidly solidified Al-5Ti-1B master alloy prepared by the in-rotating-liquid spinning process has been investigated. It has been found that the in-rotating-liquid spinning process is a potential rapid solidification method to realize the continuous production of the master alloy wire on a large scale. The microstructure of the Al-5Ti-1B was evidently improved after being rapidly solidified. The agglomeration of the TiB2 particle was significantly decreased. Consequently, the grain size of the purity aluminium refined by the rapidly solidified Al-5Ti-1B was reduced by 15% compared with that refined by the master alloy prepared under normal conditions.

Abstract: Aluminium alloys are successfully used in marine and offshore structure in purpose of cathodic protection. Aluminium itself has poor electrochemical properties for sacrificial anode applications. Hence it is alloyed with other elements to improve its characteristics. This study was conducted to investigate the influence of calcium addition and also heat treatment on the potential and current capacity of Al-Zn-In anodes. The electrochemical performance of these anodes was evaluated by electrochemical test based on NACE standard method. SEM and EDAX analyses were used to examine the surface structure of the anodic materials. The results were then compared with those of the base alloy without calcium and untreated specimens to understand the behaviour of the anode after alloying and heat treatment.

Abstract: Mechanical properties and microstructure of twin-roll cast (TRC) pure aluminium, Al-Fe-Mn-Si (AA8006) and Al-Mg (AA5754) alloy sheets ARB processed at ambient and elevated temperatures (200, 250, 300 and 350°C) were investigated. Processing at elevated temperatures results in better bonding but it produces smaller increases in hardness. AA8006 specimens were processed without any problems up to 7 cycles. The alloy AA5754 suffered from severe edge and notch cracking since the first cycle. The strength was evaluated from tensile test and microhardness measurements; the microstructure was examined using light microscopy, and transmission electron microscopy. The microstructure was compared to that of conventionally cold rolled (CCR) specimens with true strain ε of 0.8, 1.6, 2.4 and 3.2 corresponding to the strain induced by 1 to 4 ARB cycles. The work hardening of alloy AA8006 saturated after the 3rd cycle, whereas the hardness of alloy AA5754 increased steadily up to the 5th cycle. Very fine grain structure with large fraction of high angle boundaries was observed in both alloys after two cycles of ARB. The grains were refined to submicrometre and nanometre size (down to 90 nm in alloy AA5754). Intensive post-dynamic recovery was observed in AA8006 specimens. The recovery is less pronounced in the AA5754 alloy with high concentration of solute atoms in solid solution.

Abstract: The variations during isochronal annealing of cold-rolled commercial pure Al (1050) and Al-Mn (3004) has been investigated between room temperature (RT) and 823 K. The annealing stages have been identified as recovery, partial recrystallization, complete recrystallization and grain growth using positron annihilation lifetime (PAL) spectroscopy, Doppler broadening of annihilation radiation (DBAR) spectroscopy and Vickers microhardness (Hv) measurements. The retardation of complete recovery in Al-Mn alloys is due to the presence of vacancy-Mn complexes. A positive correlation has been found between positron annihilation parameters (τav & Snor) and mechanical properties (Hv) for the two alloys under investigation.

Abstract: The morphological changes and corresponding plume deflection effect during long laser (XeCl excimer laser, λ=308 nm, τ=30 ns) irradiation of Al target have been investigated,and results showed that, a the number of laser pulses per site increases, the target morphology changes and produces a visible deviation of the plasma plume up to 5º. Scanning electron spectroscopy analys of the target surface related the plume deflection angle to the target morphology and the number of laser pulses per site. Typically well-defined columnar structures oriented along the laser beam direction were observed on the target surface. The plume created during the laser ablation was clearly visible to the naked eye and was recorded by a digital camera. Detailed studies were also performed on the ablation rate at different laser fluences (4.6 J/cm2-12.5 J/cm2). The morphologies and the thickness of the Al thin films deposited on Si substrates during the present laser ablation experiments were also studied. Finally, the scenario explaining the formation of columnar structure on target surface responsible for the plume deflection effect will be discussed.

Abstract: An Al-3%Mg-0.25%Sc-0.12%Zr alloy was deformed by triaxial forging at 20-400°C up to strains of about 3. A study of its textural evolution reveals the tendency towards three symmetrical variants of a <110><1 10 ><001> component. This experimental observation is supported by a 3D spatially resolved crystal plasticity analysis. Samples strained at room temperature undergo grain fragmentation in the form of fine substructures and relatively weak textures. Conversely, at 300°C and above, more homogeneous intergranular deformation and rotations give rise to stronger textures. This eventually encourages grain coalescence and thus the development of interpenetrating “orientation chains”, creating a new type of microstructure. The influence of this texture development on the specific work hardening behaviour is discussed.