Papers by Author: D. Ripamonti

Abstract: Heat treatable aluminium alloys show their best properties when properly heat treated. Most of the high-strength alloys are usually serviced in the so-called T6 temper consisting of ageing at moderate temperature after a solution treatment and a subsequent quenching. A large extrusion was investigated in this paper. The part was solution annealed at 505°C, water quenched and aged at 160°C for 16 hours. Each stage of the heat treatment is analyzed in this paper in the light of the properties achieved, by experimental investigations and several kinds of numerical simulations. In particular, a thermodynamic calculation (Pandat® software) provides solidification temperatures and equilibrium phases, in order to check whether the solution temperature is adequate. A finite element analysis (performed with COMSOL Multiphysics® software) supplies a simulation of the temperature field during water quenching. The cooling curves obtained are drawn on CCT (Continuous Cooling Transformation) curves, calculated by means of JMatPro® software, to verify if any undesired high temperature precipitation could occur during quenching. Finally, calculated TTT (Time Temperature Transformation) curves can be related to the ageing treatment.Thermal analyses, microstructural investigations and microhardness profile measurements on extrusion sections are also performed to validate calculated results.

Abstract: A study was carried out on a ECAP processed Sc-containing Al-Mg-Si alloy and on a reference 6082 alloy to investigated grain structure evolution during severe plastic deformation and post-ECAP aging behaviour. The results showed that the mechanism of ultrafine structure development was substantially unchanged with respect to a reference Sc-free alloy. Also the aging sequence and precipitation kinetics of the two alloys revealed to be comparable. The ECAP processed samples of the 6082 reference alloy showed a clear recrystallization peak at temperatures in the range 315-360°C, depending on the amount of strain experienced, whereas the Sc-containing alloy retained its ultrafine structure up to temperatures well exceeding 450°C, under the conditions reproduced in a DSC temperature scan.