International Symposium on Processing of Metals and Advanced Materials - Modeling, Design and Properties at the 1998 TMS Annual Meeting, San-Antonio, Northern Mariana Islands, 16 - 19 February 1998, pp.195-206
To study by thermal analyses the response of precipitation hardenable alloys of Al-Cu-Mg and Al-Li-Cu-Mg system to natural and artificial ageing, a series of ternary and quaternary Al-alloys with nominal compositions of Al-1. 13wt%Cu-0.65wt%Mg (alloy-1), Al-1.15wt%Cu-0.57wt%Mg-0.07wt%Li (alloy-2), Al-1.19wt%Cu-0.56wt%Mg-0.75wt%Li (alloy-3), Al-2.01wt%Cu-0.89wt%Mg (alloy-4), Al-2.14wt%Cu-0.56wt%Mg-0.07wt%Li (alloy-5) were used in the present investigation. Samples in the form of rolled sheets are subjected to water quenching at 25EC after solution treatment at 530EC for 20 min. Alloys were aged naturally at room temperature (25EC) up to 2 months and artificially at 190EC up to 2 days. By using differential scanning calorimetry (DSC) in the temperature range of 25-300EC, differential thermal analysis (DTA) in the temperature range of 25-600EC together with Vicker's hardness measurements, the response to natural and artificial ageing of the alloys used in the present study were investigated. It was observed that in these alloys, GPB(Cu, Mg) zones [Guinier-Preston zones with Cu and Mg] do form during water quenching at 20EC following solutionizing heat treatment Natural ageing of the same alloys causes formation of more GPB(Cu, Mg) zones, which results in hardening in the alloys. Artificial ageing at 190EC up to 1 day results in GPB zone dissolution causing preliminary decrease in hardness values while two days of artificial ageing in the alloys cause S' (Al2CuMg) precipitation confirmed by DSC/DTA analyses resulting in an increase in hardness values. Li addition up to 0.75wt% helps T-1 (Al2CuLi) and T-1 (Al6CuLi3) phase formation together with S' precipitation as DSC/DTA analyses show after the same heat treatment.