PSI - Issue 23

Barbara Nasiłowska et al. / Procedia Structural Integrity 23 (2019) 583 –588 Nasiłowska B. / Structural Integrity Procedia 00 (2019) 000 – 000

585

3

c

b

a

5

R ≥ 20

20

35

45

220 120

45

Fig. 1. (a) dimensions of the 5754 aluminium alloy sample with a joint made with the TIG method for mechanical tests; (b) the Instron 8862 stand for tensile tests (c) with the sample

1.5. LIBS analysis The LIBS (Laser-Induced Breakdown Spectroscopy) method is based on heating and evaporation (ablation) of material upper layer using laser pulse and generation of plasma which emits continuum and line radiation. Analysis of the line radiation emitted from plasma allows to identify elements along different depths in upper layer (in the stratigraphy mode of measurement). After focusing laser beam onto aluminium alloy surface a small part of the material undergoes ablation and in result of absorption of laser radiation plasma is generated. In plasma radiation spectral lines of elements evaporated form sample surface can be observed. Analysis of the spectra allows to obtain qualitative information on chemical composition of upper layer of the 5754 aluminium alloy after shot peening. 2. Research object Welded joints in the 5754 aluminium alloy made of the TIG method were analyzed with respect to static tensile test and microfractography after shot peening. Chemical composition of the tested samples is shown in Table 1 (PN EN 1706:2011).

Table.1 Chemical composition of the 5754 aluminium alloy (PN-EN 1706:2011) Mg Mn Fe Si Zn Cu

Cr

Ti

2.6 – 3.6

5754

>0.5

>0.4

>0.4

>0.20

>0.1

>0.03

>0.15

3. Characteristics of the joint structure Analysis of structural changes in the zone of the 5754 aluminium alloy joint welded using the TIG method showed that in the fusion lines at the grain boundaries the material was partially molten. At the boundary of a fusion zone diffusion processes occur causing a change in alloying components which has an influence on strength properties. In the vicinity of a fusion line a coarse-grained material structure characterized by a few times larger aluminium grains was observed (Fig.2a). At the grain boundaries in the heat affected zone a disruption in the periodic crystal structure characterized by atomic lattice misfit of the adjacent grains was observed (Fig.2b). Analysis of the disorientation of adjacent crystals revealed the presence of high- angle boundaries (> 15°) (Fig.2b).