Materials Science Forum Vols. 519-521

Abstract: In this study, asymmetric warm rolling (AWR) has been applied to improve the formability of bake-hardenable Al-3mass%Mg-1mass%Cu-(Ag) alloy sheets. The T4 sheets by the AWR are superior to those by conventional rolling (CR) in Lankford value and drawability. This improvement is caused by a change in the recrystallization texture to have a predominant orientation close to {111}//ND. The unusual texture for recrystallized aluminum alloy sheets is due to the shear deformation introduced during AWR. The Al-Mg-Cu alloy sheets by AWR have been confirmed to possess combined bake-hardenability and the improved formability. However, the bake-hardening response of the Al-Mg-Cu alloy by AWR is slightly inferior to that of the identical alloy by CR.

Abstract: Through-Process modelling (TPM) of microstructure evolution during thermomechanical processing of sheet produced from direct chill (DC) cast non-heat treatable aluminium alloys is discussed. In a companion paper [1] the upstream processes of casting and homogenisation were dealt with, whereas the present paper focuses on the downstream deformation and annealing steps. Some recent advances in relevant model development are reviewed, and the important microstructural descriptors and their interactions are outlined. Together with two application examples – coiling of hot strip, and cold rolling of foil – current knowledge gaps in theory and modelling capability are highlighted.

Abstract: In metallic alloys, the formation of macrostructure involves different length and time scales. The macrostructure strongly influences the mechanical properties of the materials. Modeling of macrostructure provides valuable insights for tailoring of the macrostructure. In the present study simulation of macrostructure in Al-22Sn has been carried out. Expression for nucleation rate and growth rate were tuned to get a match with the experimentally observed macrostructure. The study incorporates the motion of grains due to Brownian motion. Incorporation of Brownian motion resulted in more uniform distribution locally, which has been experimentally observed. Both simulation and macrograph showed few columnar grains and absence of sharp columnar to equiaxed transition.

Abstract: A heat transfer model was built to predict the temperature evolution of semi-solid aluminum billets produced with the SEED process. An inverse technique was used to characterize the heat transfer coefficient at the interface between the crucible and the semi-solid billet. The effect of several process parameters on the heat transfer coefficient was investigated with a design of experiments and the coefficient was inserted in a computer model. Numerical simulations were carried out and validated with experimental results.

Abstract: Impact properties and fatigue crack growth behavior of a newly developed Al-Zn-Mg functionally graded material (FGM) is studied. The gradient in terms of hardness (about 85 to 130 VHN) and yield strength (about 260 to 360 MPa) is established along the width of the Charpy-impact and Compact Tension specimens. In both these test specimens two types of FGMs, depending on the direction of crack propagation, are produced. In the first case, FGM-I, the notched surface is made harder and the hardness value decreases towards the other surface in the direction of crack growth. In the second case, FGM-II, the hardness gradient is reversed and the crack propagation takes place from the softer side to the harder side. The impact and fatigue crack growth experiments are also carried out for the homogeneous materials with different hardness values and the results obtained from the FGMs are compared with them. The results of impact tests show that FGM-II absorbs about 20% greater energy than the highest energy absorbed by any of the isothermally aged homogeneous materials. Fatigue crack growth studies for the FGM-I show a reduction in crack growth rate as the crack propagates towards softer (ductile) side and finally crack arrest is observed. On the other hand, for the case of FGM-II, where the crack propagates towards the harder side, the crack growth rate first increases and then decreases. However, in this case the crack follows a tortuous path and it starts bending upwards after about 20 mm crack length, which might be responsible for higher energy absorption in impact tests.

Abstract: The effect of different parameters during thermo-mechanical processing on the earing behavior of AA3003 aluminum sheets has been investigated. These were homogenization of the cast strip, cold rolling, intermediate and final annealing of the sheets at different gauges. The amount of 0/90° earing formed on annealing decreased with cold rolling prior to annealing. Nevertheless, annealing after partial deformation gave rise to large amounts of 0 to 90° ears to balance subsequent ±45° earing. Homogenization prior to cold rolling resulted in a fine dispersoid distribution which, in turn, increased the tendency for 0/90° earing. All of these observations were consistent with textural studies in which cube and rolling textures were competing to produce positive and negative earing, respectively. It is concluded that the "non-earing" quality in the present material could be obtained by proper combination of processing variables such as; homogenization, cold reduction, and annealing cycles.

Abstract: Commercially pure aluminum (A1050) sheets have been cold- rolled in vacuum, to obtain high friction between rolls and sheet. This cold-rolling in vacuum successfully introduced large shear deformation near the sheet surface. The shear strain is the highest at the sheet surface, and rapidly decreased to zero at the quarter thickness. These high shear strains are sufficient enough to produce {111} and {001} cold- rolling, or shear texture. Conventional cold-rolling texture such as (001) [100], is naturally observed at the mid-thickness. It is confirmed that a high shear strain and probably steep strain gradient through thickness have a sufficient effect on the increase in {111} cold-rolling texture near the sheet surface. {111} cold-rolling texture is proved to be effective in the evolution of {111} recrystallization texture. This development will be discussed based on the cold-rolling texture change.

Abstract: A new method is introduced to determine the absolute value of the boundary excess free volume. Along with the boundary energy the excess free volume belongs to the major thermodynamic properties of grain boundaries. The method utilizes the dependence of the contact angle at triple junctions of grain boundaries in Al-tricrystals on hydrostatic pressure. We investigated <111> tilt boundaries in the pressure range up to 14 kbar. In particular, for a 40° <111> tilt boundary with 2° twist component the boundary free volume was found to be equal to 5.03×10-11 m3/m2.

Abstract: In order to predict the mechanical properties of Al sheet products, the evolution of microstructure and crystallographic texture along the process chain must be tracked. During the thermo-mechanical processing in commercial production lines the material experiences a complex history of temperature, time and strain paths, which results in alternating cycles of deformation and recrystallization with the associated changes in texture and microstructure. In the present paper the texture evolution of AA 3104 can body stock is modelled. In particular, the earing behaviour at final gauge is linked to the decisive steps of deformation and recrystallization along the thermomechanical process chain. For this purpose, the textures predicted by a comprehensive throughprocess model of the texture evolution during the thermo-mechanical production of Al sheet are input into a polycrystal-plasticity approach to simulate earing of the final gauge sheets.