PSI - Issue 13

Lenka Kuchariková et al. / Procedia Structural Integrity 13 (2018) 1577–1582 Lenka Kuchariková / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 1 Microstructure of A226 cast alloy. (a) metallographic observation of microstructural components in as-cast state, etch 0.5 % HF; (b) 3D morphology observation in as-cast state, etch HCl; (c) metallographic observation of microstructural components in the T6 state, etch 0.5 % HF; (d) 3D morphology observation of the deep etched microstructural components in T6 state of A226 cast alloy, etch HCl. For each microstructural component, all the techniques of the EDX analysis were used for observations (Fig. 2). Mrówka (2011) and Rios (2003) examined how the presence of Cu in unmodified aluminium alloys leads to forming phases such as Al 2 Cu with tetragonal crystal structure, which solidified in two morphologies after the Al-Si eutectic reaction. The first is as massive or blocky form (Al 2 Cu) with the high copper concentration (38 - 40 %) and the second is as the fine ternary eutectic form (Al-Al 2 Cu-Si). Those studies confirmed the presence of both types of the Cu-rich phases in microstructure of experimental secondary A226 cast alloy. The type was determined based on the EDX analysis (Fig. 2a). The results of the line analysis showed that the first Cu-rich phases (ternary eutectic Al-Al 2 Cu-Si) have Al, Si and Cu and the second Cu-rich phases (Al 2 Cu) have only Al and Cu.

Fig. 2 EDX analysis of microstructural components morphologies. (a) Al 2 Cu and the ternary eutectic phases and their line analysis; (b) 3D morphology of Fe skeleton-like phases, deep etching with HCl and its mapping analysis; (c) Al 5 FeSi phase and its line analysis. Etch 0.5 % HF.

From the iron-rich second (intermetallic) phases the following two types were observed: Al 5 FeSi with monoclinic crystal structure (the β -phase) and Al 15 (FeMn) 3 Si with the cubic crystal structure (the α -phase), Fig. 2b,c. Mapping EDX analysis confirmed presence of Al, Si, Fe and Mn in composition of the Fe-rich phases in the skeleton-like form (Fig. 2b). The point analysis of Al 5 FeSi phases was difficult (Fig. 2c), because they are very thin. The laser beam is wider than these phases, so the results are not correct (Table 2). The better results were obtained by the other two EDX analyses. Table 2. Results of the Al 5 FeSi phases point analysis. Elements AN Series unn. C [wt. %] norm. C [wt. %] Atom. C [at. %] 1 Sigma [wt %] Al 13 K-series 87.50 73.71 79.47 4.42 Si 14 K-series 15.97 13.46 13.94 0.76 Mn 25 K-series 2.14 1.80 0.95 0.10 Fe 26 K-series 11.1 9.35 4.87 0.33 Cu 29 K-series 2.0 1.68 0.77 0.10 TOTAL 118.71 100 100