Characterisation of dynamic recovery during hot deformation of spray formed Al–Li alloy (UL40) using processing map approach

Abstract

Processing maps, also known as power dissipation maps, for spray formed Al-Li alloy (UL40), encompassing a wide range of hot working temperature (375-575uC) and strain rate (3610 24 -10 1 s 21 ) have been developed. The constant true strain rate compression tests were carried out under isothermal conditions to generate the stress-strain data required for computing the efficiency of power dissipation g. The maps exhibit three distinct regimes. The two high efficiency (.55%) regimes occur at the low strain rates (,10 23 s 21 ) and at the high strain rates (.1 s 21 ), and the other with moderate efficiency values (20-23%) occurs at the intermediate strain rate (10 21 s 21 ). The latter one has been interpreted to be associated with dynamic recovery (DRV) process while the other two regimes have been found to be associated with cracking processes. The DRV regime in the map has been characterised in terms of stress-strain response, microstructure and tensile ductility. The kinetic rate analysis carried out in the DRV regime suggested that the thermally activated cross-slip is the rate controlling mechanism for the DRV process. The effect of Li addition on the optimum deformation condition of DRV in Al has also been discussed qualitatively.

Effect of HIPing on microstructure and properties of spray formed Al–Li alloy UL40

“…This is related to (i) the changes in the volume fraction and distribution of d precipitates on the dynamic restoration processes (not investigated here) (ii) due to the lower concentration of d and therefore less oxidation damage during the tests (iii) the removal of porosity. The temperature range of 425-525uC (698-798 K) fell in the dynamic restoration regime, 20 and must have led to microstructural changes amenable to continued plastic deformation, explaining the high ductility exhibited. It may be mentioned here that other Al-Li alloys have also been reported to exhibit high ductility in the closely matching temperature range of 400-500uC (673-773 K).…”

Comparative study of hot-processing maps for 6061 aluminium alloy constructed from power constitutive equation and hyperbolic sine constitutive equation

“…The hot-processing map, which can be divided into a safe domain and an unsafe domain, is a superimposition of a power-dissipation map and an instability map. This methodology has been used to optimise the hot workability of materials such as aluminium alloy, [5][6][7] magnesium alloy, [8][9][10] titanium alloy, 11 and others. [12][13][14][15][16] To avoid the complicated integral, the power constitutive equation s~K : e m is commonly used to represent flow behaviour of a material in constructing a hotprocessing map.…”