Abstract
In this paper, the evolution of the microstructure and mechanical properties on the AA2024 alloy was studied during the over-ageing process. The phenomenon of precipitation hardening in aluminum alloys allows the precipitation of the intermetallic particles, starting from the main elements of alloy (Cu and Mg), process realized to a relatively low temperature (100-200°C). The fundamental stage in the age-hardening process allows the acceleration of the decomposition phenomenon of the supersaturated solid solution, resulting in a precipitation of the intermetallic particles; stage where the mechanical properties reaches the maximum values, but at the cost of a low corrosion resistance. The over-ageing treatment (T7) is supposed to stabilize the microstructure and to improve the corrosion resistance. The over-ageing treatment was realized at three different temperatures: 150°C, 175°C and 190°C. For each temperature, the treatment duration (36 days for 150 ° C, 50 h for 175°C and 24 h for 190 °C) was determined by a given Vickers macrohardness reduction. To characterize the microstructure of alloy 2024-T7, a statistical analysis of the spatial distribution of intermetallic particles was made, depending on the surfaces fraction and density. In the same time was observed the evolution of the intermetallic particles dimension depending on the temperature of the treatment. In this purpose were analyzed the SEM images acquired in a backscattered electron way using the Areas software. The mechanical properties of the matrix of the AA2024 alloy and its coarse intermetallic particles before and after thermical treatment were characterized using an MTS Nanoindenter with a Berkovich indenter tip.
Keywords: Heat Treatment, Microstructure, Size Distribution, Mechanical Properties