Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: E. Gariboldi x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Heat-treatable aluminium alloys are widely used for structural applications. Their strength is obtained through age hardening phenomena, that are sensitive to microalloying. In the present paper the results of thermal analyses on the ageing behaviour of an Al-Cu-Mg-Si alloy with silver and zirconium additions are presented. Specimens were water quenched after solution heat treatment, then aged at 453 K and a hardness-versus-time plot was drawn. Samples representative of different ageing conditions were subjected to DSC scans. Peaks were identified taking into account θ and Q phases precipitation sequences. Solution treated samples showed GP/θ″/θ′/Q sequence, while in peak aged condition GP and θ″ precipitation peaks disappeared and a reduction of θ′ peak area was observed, witnessing the concurrent presence of θ″ and θ′ phases at peak hardness condition. Experimental data were compared with results from analogous investigations performed on a conventional commercial Al-Cu-Mg-Si alloy.

Restricted access

Abstract  

An Al–4.4Cu–0.5Mg–0.9Si–0.8Mn alloy (IADS 2014 grade) in the solution annealed and peak aged condition was exposed at 170°C for relatively long times (up to about 1800 h) in order to check the stability of the alloy. The investigated aging temperature was in the frame of a research on the long-term mechanical behaviour of such alloy. Microstructure evolution was monitored via calorimetric analyses, metallographic inspections and hardness measurements. Further, X-ray analyses were carried out on selected samples. The attention was focused on differential scanning calorimetry performed at different scanning rates, with the aim of evaluating the kinetics of the precipitation phenomena. Notwithstanding the wide industrial diffusion of this alloy, literature survey showed that there is not a consensus view on the precipitation sequences and on calorimetric peak identification. The present results show the progressive evolution of calorimetric peaks, corresponding to that of strengthening particles towards more stable phases, proved by the disappearance of exothermic peaks. Activation energy from Kissinger kinetic analysis in the case of aged samples provided scattered values that could be reasonably attributed to an overlapping of transformation peaks. Moreover, in these samples transformations partially occurred before DSC scans, providing non-constant transformation fraction at signal peak temperatures and resulting in different activation energies.

Restricted access

Summary Calorimetric analysis is commonly used for the study of several solid state transformations, among which phase transformations. Information about enthalpy, kinetics and general features of transformations could be obtained with suitable configurations of the analysis equipment and arrangements of the tests procedures. An experimental analysis of the transformation occurring in a Mg-Al-Mn alloy, namely AM60, has been performed on samples cut from as die-cast components. The results obtained confirmed that calorimetric analysis is a suitable method for the study of transformations of such kind of alloys. Using the technique of multiple heating rate tests, an estimation of activation energy of dissolution of Mg17Al12 phase has been derived.

Restricted access