Abstract
Usually strength-toughness combination in aluminum alloys is improved by heat treatment (solid solution followed by quenching and reheating) after a deformation process at high temperature. In some cases a cold working step is added in the manufacturing process before heat treatment aimed to enhance the alloy strength. In recent time, some trials have been carried out finalized to replace the cold working step with a warm deformation. Such process route appeared to be quite effective in improving the toughness behavior of 7xxx alloys. Anyway e metallurgical explanation for such behavior has not still be reported . In this a comparison of the precipitation state following the two different routes is reported. Results show clear differences in the nanoprecipitation densities in the two cases, claiming for their responsibility in the definition of the toughness behavior.
Highlights
Light alloys were considered for a long time the best solution for most the high-tech applications, including sport equipment [1], energy and automotive [2]
The effect of the up-setting temperature increase on microstructure is shown in Figures 2 and 3: results clearly show a grain size refinement
It is worth to be noted that an upsetting increase up to 473 K resulted in a 10% toughness improvement in terms of KIC, with respect to material processed in standard condition
Summary
Light alloys were considered for a long time the best solution for most the high-tech applications, including sport equipment [1], energy and automotive [2]. AMS 4333 International Standard calls for an intermediate cold working process step, with a maximum 5% allowed cold upsetting, to be performed before the two ageing final steps, after the solution heat treatment This with the aim to best define the precipitation state (in terms of precipitation size distribution) so assuring the best achievable mechanical properties combination [21]. Concerning this topic, Wyss et al proposed the US Patent [22], showing beneficial effect due to an intermediate warm hardening process step, to be executed instead of the standard cold upsetting, on the facture toughness properties Such process route appeared to be quite promising in the case of 7xxx alloys: in particular an improvement of toughness was found without any deterioration of hardness and tensile behavior [23]. In this paper the effect of process routes on the precipitation size distribution is reported
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