【正文】 iven ageing temperature, the sequence and type of phases that form are strongly position dependent. These in turn are determined by the equilibrium phases that may eventually form in these alloys. Evolution of equilibrium phases for any given position and temperature can be calculated using the CALPHAD procedure [19,20]. It is well known that crystallographic texture controls the formability of the Al alloys. Crystallographic texture develops in metals and alloys when subjected to large deformation and/or annealing. Rolling/deformation textures in Al alloys are characterized by the β fiber running from copper orientation {112} ﹤111﹥over the S orientation {123} ﹤634﹥ to the brass orientation {011} ﹤211﹥. The recrystallization texture ponent is dominated by strong cube orientation {001}﹤100﹥ and Goss orientation {110} ﹤001﹥[21].In this work, a modified version of age hardening AA6061 alloy (designated as 6061M) was subjected to rolling at liquid nitrogen 09215093/ temperature (77K) (here after referred to as CR) and at room temperature (here after referred to as RT). We present the microstructure, texture and mechanical properties of the alloy 6061M in the rolled (CR and RT) and in the rolled and aged conditions. The differences between the conventional AA6061 and 6061Mare explained on the basis of phase fraction calculations for the alloys using CALPHAD procedure.2. Experimental procedureThe 6061M alloy was procured in the form of plates of thickness. These plates were solutionised at 535 ℃ for 1 h and quenched in water and subsequently rolled (at room temperature and at liquid nitrogen temperature) from to in multiple passes with about 10% reduction per pass. For rolling at liquid nitrogen temperature, the solutionised plates were dipped in liquid nitrogen for 15min and after each pass the plate was immersed in liquid nitrogen for 2 min before further reduction. Differential scanning calorimetry (DSC) was used to identify the recovery and recrystallization temperatures of the alloy. To study the age hardening behaviour, the CR and RT rolled samples were subjected to ageing at 100, 125 and 150 ?C for varying times (1–36 h) in a tubular furnace. Vickers hardness was measured using 100 g load on rolled and aged samples. Xray diffraction was done on CR, RT rolled and annealed samples using the CuK radiation. Pure Al powder annealed at 300 ?C in Ar atmosphere was used as reference in XRD peak broadening for microstrain calculation. Uniaxial tensile tests were conducted at an initial strain rate of 310?3 s?1 on specimens that were machined as per ASTM E8 subsize specifications. For Xray texture analysis {200}, {111}, {110} and {113} pole figures were measured (on the surface of samples) on a Phillips Xray texture goniometer using CuK radiation. From inplete pole figure data, orientation distribution function (ODF) and quantitative texture ponents are calculated using LABOTEX software [22]. Microstructural characterization was carried out using Philips CM12 transmission electron microscope (TEM) operating at 120 kV.3. Results and discussionThe chemical position of the alloy (6061M) is given in Table 1. The position was determined through spark emission spectroscopy. It may be noted that in 6061M, the Mn, Cu and Cr contents deviate from standard specification of AA6061 [23]. The equilibrium phase fractions in these alloys was calculated using the well known putational thermodynamic software ThermoCalc [24]. It is clear that the amount of strengthening precipitates Al6Mn and AlCu (θ) available at any given temperature is higher in the case of 6061M pared to AA6061 (Fig. 1), while Mg2Si content is similar. Moreover, unlike alloy AA6061 the plete dissolution of these precipitates was not possible by solutionising heat treatment in the case of 6061M. These differences will have significant effect on the microstructure and mechanical properties of the alloy 6061M and these are discussed later in the paper.Table 1 Chemical position of 6061M and AA6061 alloy in wt%.AlloyMgMnSiFeCuCrAl6061MBalanceAA6061BalanceFig. 1. Phase fraction plot for (a) alloy 6061M and (b) alloy AA6061 showing dependence of phases on position and temperature.Fig. 2. DSC curves of CR and RT 6061M alloy indicating the recrystallization temperature regime.The DSC results of the CR and RT AA6061 samples are shown in Fig. 2. Fromthe DSC curve it can be seen that the onset of recrystallization (the onset of the major exothermic peak in DSC) occurs at 200 ℃ in both the samples and the peak in the exothermic event in both the samples also occurs at the same temperature (250 ℃). The stored energy released during the major exothermic event is believed to be predominantly due to recrystallization and precipitation from the supersaturated matrix of the rolled alloys. The amount of energy released (area under the exothermic event) is similar in both the CR ( J/g) and RT ( J/g) samples. This indicates that the amount of stored energy due to the deformation in both the conditions is about the same. The stored energy after deformation is related to the stacking fault energy (SFE). The parable stored energies in the CR and RT samples indicates that the defect densities in both the samples are same. This is surprising as CR sample is expected to have higher defect density. This indicates that the SFE of the 6061M alloy is relatively high, due to which cross slip is promoted even at very low deformation temperatures. (It may be noted that Al and Ni are considered to be higher SFE materials, Cu medium SFE material and Ag low SFE material.) This has implications for the microstructure that develops during rolling which is discussed later in the paper.Table 2 The volume fraction in % of the main texture ponents in CR and RT condition in alloy 6061M.Rolling texture ponentsRecrystallization ponentsample Copper{112}111Brass{110}112S{1