Issue 35

A. Tzamtzis et alii, Frattura ed Integrità Strutturale, 35 (2016) 396-404; DOI: 10.3221/IGF-ESIS.35.45 399 E XPERIMENTAL SIMULATION OF HAZ LOCAL PROPERTIES Microstructural Characteristics imulation of HAZ material properties was achieved by implementing a heat treatment procedure on 2024 material described in [14] using different overaging conditions. The procedure selected helps to produce materials based on the 2024 alloy with similar microstructural characteristics and local properties with selected positions in the HAZ, without the weld residual stresses. The overaged materials exhibit similar local properties and microstructural characteristics with 3 locations in the HAZ: (a) close to the base material, (b) at the mid-point of HAZ hardness gradient and (c) close to the weld nugget (HAZ/TMAZ interface), and are named A200, A250 and A300 respectively, based on the temperature of heat treatment used for 15 hours aging. The microstructural characteristics between the HAZ material (close to the base metal, 12 mm away from the weld center) and A200 are given in Fig. 2. They are comparable and consist of same size coarsened second-phase particles, the Al 2 Cu (θ΄phase) and the Al 2 CuMg (S΄ phase). In both materials similar hardness values are obtained as shown in the hardness profile of the 2024 aluminum alloy FSW, in Fig. 3. In the same Figure, the hardness values of materials A250 and A300 are shown and are placed on the respective locations in the HAZ with similar hardness values. (a) (b) Figure 2 : Microstructures of (a) HAZ at a distance 12mm from the weld centerline, (b) A200 material. Figure 3 : Microhardness variation in 2024 FSW determined at two different layers in the cross section of the FSW joint (1 and 2 mm depth from specimen surface). Local hardness values of A200, A250 and A300 materials are shown at the locations in the HAZ with similar microhardness values. The specimen location designates where the sample has been extracted to obtain local tensile properties in the HAZ. S specimen location