Materials Science and Engineering A 420 (2006) 228–234 Development and characterization of Al–Li alloys R.K. Gupta a,∗ , Niraj Nayan b , G. Nagasireesha b , S.C. Sharma b a Mechanical Engineering Entity, Vikram Sarabhai Space Centre, Trivandrum 695022, India b Materials and Metallurgy Group, Vikram Sarabhai Space Centre, Trivandrum 695022, India Received 26 July 2005; received in revised form 4 January 2006; accepted 17 January 2006 Abstract Increased strength to weight ratio of aluminium–lithium alloys has attracted material scientists to develop these for aerospace applications. But commercial scale production of these alloys has always been slow in view of difficulties encountered during addition of lithium and in ensuring homogeneous billet composition. A new technique of Li addition has been adapted, which gives maximum recovery of Li in the billet. Using this technique, aluminium–lithium alloys of two different grades for aerospace application were cast. Billets were hot forged and rolled to the thickness range of 3–4 mm and heat-treated for different temper conditions. Mechanical properties were evaluated in T6 (solution treated and artificial aged), T8 (solution treated, cold worked and artificial aged) and T4 (solution treated and natural aged) temper conditions. Both alloys exhibit a strong natural aging response. Reversion for short periods at 180 ◦ C results in decrease of strength. With artificial reaging strength reaches above the T4 temper condition level. Characterization was carried out using optical microscope (OM) and scanning electron microscope (SEM). Experimental investigation shows that addition of lithium at high melt temperature gives lower recovery of Li, and use of impure aluminium adversely affects the mechanical properties of the alloy in all temper conditions. © 2006 Elsevier B.V. All rights reserved. Keywords: Al–Li alloy; Casting; Homogenization; Precipitation 1. Introduction Right from inception of space programme, aircraft engineers and manufacturers have demanded materials with high spe- cific strength to increase the payload capability. The family of lithium containing Al alloys has received much attention for use in weight-critical and stiffness-critical structures for mili- tary, space and commercial application because they offer low density, improved specific strength and high stiffness to weight ratio as compared to the commercial 2XXX and 7XXX series aluminium alloys and carbon fibre composites [1–3]. But its commercial application could not be realized for long time after its development because of its low ductility and tough- ness. For last four decades development of Al–Li alloy is being carried out worldwide. A number of alloys with different Li and Cu contents with better mechanical properties have been developed. It has been found that, addition of 1% of lithium to aluminium reduces alloy density up to 3% and increases ∗ Corresponding author. Tel.: +91 471 2563916; fax: +91 471 2705427. E-mail addresses: guptarohitg@rediffmail.com, rohitkumar gupta@vssc.org (R.K. Gupta). modulus by 6%. But the amount of lithium addition is limited, since strength is strongly dependent on Li content as it exhibits erratic behaviour beyond a certain level. It has been observed by Lagan and Pickens [4] that increasing the alloy’s Li content above 1.3 wt% results in decrease in both yield stress and tensile strength, whereas maximum strength is obtained in the range of about 1.1–1.3 wt% lithium [4]. It was noted that minor addi- tions of Zr, Ag, Mg and rare earth metals to Al–Li–Cu alloys exhibited a very good combination of strength and toughness during the development of Weldalite 049 [5]. Weldalite 049, with a high Cu/Li ratio and with a nominal composition of Al–6.3Cu–1.3Li–0.4Ag–0.4Mg–0.14Zr [6] is found to be the best in terms of mechanical properties and weldability. Space industries selected this alloy for making liquid propellant tanks (both cryogenic and earth storable tanks) of launch vehicle as its ductility and toughness did not deteriorate even at low tem- perature. This paper presents developmental attempt made to realize such an alloy, which includes melting and casting of the alloy with different Li contents, design of homogenization cycle and mechanical working i.e. forging and rolling to 3–4 mm thick sheets. Rolled sheets were heat treated in different temper con- ditions and mechanical properties have been evaluated which 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.01.045