Papers by Keyword: Al-Fe-Mn-Si Alloy

Abstract: Accumulative Roll Bonding (ARB) is a severe plastic deformation process that allows producing ultrafine-grained materials (UFG). UFG sheets exhibit enhanced strength and very fine grain structure. Foils used as fins in heat exchangers have to be very thin but must exhibit high strength combined with relatively high formability. Thus, materials produced using ARB may fulfil the exacting requirements on foil properties for such applications. The thermal stability of Al-Fe- Mn-Si foils produced using ARB and subsequent cold rolling was studied and compared with conventionally cold rolled (CCR) counterparts. The stability was assessed by isothermal annealing in the temperature range from 200 to 450 °C. Electron back scatter diffraction in a scanning electron microscope and transmission electron microscopy examinations of foils microstructure in the deformed and annealed states allowed the monitoring of structural changes. The magnitude of mechanical properties changes due to annealing was evaluated by microhardness measurements. Significant hardness increase was observed after annealing at 200 °C only in the ARB samples and was assigned to an annealing-induced hardening. The CCR foil exhibits higher non-recrystallized fraction and smaller mean lamellae boundary spacing in the temperature interval of 200-250 °C than ARB foils. The annealing at 450 °C results in identical hardness values and fully recrystallized microstructure of all foils, regardless the method used for their manufacturing. However, the ARB samples show higher stability of the refined substructure than their cold rolled counterparts due to continuous recrystallization occurring in the ARB foils.

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.