PSI - Issue 23

Petra Ohnišťová et al. / Procedia Structural Integrity 23 (2019) 469 –474 Petra Ohnišťová et al. / Structural Integrity Procedia 00 (2019) 000 – 000

471

3

Table 1. Chemical composition of 7475-T7351 alloy.

Table 2. Mechanical properties of the 7475-T7351 alloy.

Element

Weight content [%]

Thickness of the blank sheet [mm] Tensile strength [MPa] Yield strength [MPa]

25-38 50-63 75-89

Si Fe Cu Mn Mg Cr Zn Ti

0.10 max. 0.12 max. 1.20 - 1.90 0.06 max. 1.90 – 2.60 0.18 – 0.25 5.20 – 6.20% 0.06 max. 0.05 max.

490 414

476 393

448 365

Elongation [%]

9

8

8

Others, each

Al

Balance

To analyze microstructure of aluminum alloy 7475-T7351 the EBSD study was performed. The heavily deformed structure with high anisotropy of the grains (and very fine sub-grains) was found, see Fig.1.

Fig. 1. Structure of aluminum alloy 7475-T7351 (a) longitudinal direction; (b) transversal direction.

The EDX study and STEM TEM lamella analyses allowed to observe three different secondary phases embedded in the material matrix. The first type found were the coarse intermetallic particles Al 7 Cu 2 Fe; Al-Cr-Fe-Cu-Si that had been formed during the solidification, in dimensions from 2 µm up to 20 µm. The second type of secondary phases can be described as dispersoid precipitates Al 12 Fe 3 Si; Al 12 Mg 2 Cr, that were formed in solid state due to the precipitation at the grain boundaries. The third sort of the phases in the material matrix can be characterized as fine metastable precipitates (size 2 nm – 0.6 µm) responsible for strengthening of the alloy (via GP, ή or η ), see Fig.2 .

Fig. 2. STEM TEM lamella of aluminum alloy 7475-T7351 – occurrence of the secondary phases.