Papers by Keyword: T₁ Phase

Abstract: The influence of larger pre-strains, than are currently used in industry, has been investigated on the ageing behaviour of the Al-Cu-Li alloy 2195 - in the context of producing near-net-shape, taper-rolled, thickness-tailored, plates for aerospace applications. FE modelling and simulations have demonstrated it is viable to stretch plates with rolled tapers of up to 1:1.6 in thickness. Increasing the pre-strain level at the thin end of the plate, up to 15%, resulted in a continued increase in microstructure refinement and yield strength, which rose to ~ 670 MPa without an unacceptable loss of ductility. It is shown that, even with such high pre-strains, a relatively low level of recovery occurs after artificial ageing and increasing the pre-strain is predicted to result in a reduction in strengthening from the T₁ phase, due to precipitate refinement, in favour of a higher contribution from strain hardening.

Abstract: The competitive precipitation behavior between T₁ and σ phases in Al-Cu-Li alloy was studied by hardness test, XRD and TEM observation. The hardness test results show that the changing curves are related to the densities of vacancies and dislocations, and competitive precipitation between age hardening precipitates. T₁ phases give rise to the rapid age hardening. XRD results indicates that there exists an alternation increase in peak value of diffraction intensity ranged from 40 to 45° of the aged alloy for various ageing time. About four precipitation sequences occur during ageing of Al-Cu-Li alloy, including δ', θ, T₁ and σ sequences. Competitive kinetics between T₁ and σ phases result in the phenomenon of different precipitation behavior.

Abstract: Aging behavior of Al-2.1Li-2.9Cu-0.12Zr(wt%) alloy has been studied as functions of aging time and temperature by using a differential scanning calorimetry(DSC) and transmission electron microscopy(TEM). The aged specimens at 130, 160, 190°Cwere compared with the as-quenched specimen in view of the aging behavior by observing the reaction enthalpy during the heating period of DSC experiments. DSC peak associated with the formation of GP zone is not observed at 130 and 160°C, but it does at 190°C, so it is found that the thermal stability of GP zone is changed at between 160 and 190°C. At the aging temperature of 130°C, the heat absorption corresponds to the formation of δ´ increases, while the heat evolution related with the formation of T1 reveals an opposite trend. In aging temperature of 160 and 190°C, aging time representing the drastic decrease of heat absorption of δ´ is coincident with the transition time showing the decreasing of heat evolution of T1. The micro-Vickers hardness of the specimens aged at 160°C and 190°C shows maximum values about 182 and 165 at aging times of about 72 hr and 25hr, respectively. From comparing reaction enthalpies for the dissolution of δ´ and the formation of T1 phases with the aging time showing the maximum hardness, it is found that δ´ phase rather than T1 phase markedly contributes to the hardening at an aging temperature of 160°C. In contrast, T1 phase plays an important role in hardening at an aging temperature of 190°C.

Abstract: The effect of beryllium (Be) on the precipitation behaviors and mechanical properties of Al–Cu–Li–Mg–Zr–(Ag) alloys was investigated. The results show that adding 0.02%Be to Al–Cu–Li–Mg–Zr–(Ag) alloys, the elongation of the alloy increased without significant decrease in strength and the aging response was accelerated. In a Al–Cu–Li–Mg–Zr–(Ag) alloy, G.P. zone was formed at early aging time (2 h) and T1 and q′ phases were formed at peak-aging and over-aging times, while in Al–Cu–Li–Mg–Zr–(Ag)–Be alloys T1 and q′ phases were formed at early aging time (2 h) and the density of q′ phase was very low and fine T1 phases were homogeneously distributed at peak-aging and over-aging times.