Crystallization of aluminium matrix composites reinforced with SiC
Andrzej Białobrzeski, Maksymilian Dudyk, Krzysztof Kosibór Akademia Techniczno-Humanistyczna, ul. Willowa 2, 43-300 Bielsko-Biała
Annals 2 No. 5, 2002 pages 399-403
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abstract Investigation have been centered around composites consisting of AK7 matrix alloyed with magnesium and reinforced with 5 or 10 mass % of silicon carbide particles. Composites of AK11 magnesium-free matrix reinforced with the same quantities of reinforcing particles have been prepared additionally, for the purpose of comparison. Figures 1-6 present graphic records of crystallization curves: thermal, t = f(τ) and dt/dτ = f(τ), and electric, σ = f(τ) and dσ /dτ = f(τ), obtained simultaneously by the ATD-AED method. The tables beneath the figures give the values of the temperature and the electric conductivity in characteristic „peaks” of first derivatives. Figure 7 shows comparative graphs for pure matrices and the produced composites. Results of metallographic examinations are presented in Figures 8 and 9. An advantageous influence of magnesium on the composite production process has been found while introducing the reinforcing particles into the AK7 matrix. On contrary, a significant amount of slag has been obtained for AK11 magnesium- free matrix. An analysis of the ATD-AED curves reveals significant differences between graphic profiles of temperature and electric conductivity recorded for AK7 silumin and composites with such a matrix. Silicon carbide addition has caused appearing of one more peak, designed as TA at thermal curves (Figs 2, 3), representing the crystallization of ternary eutectic α+Mg2Si+Si. The crystallization temperatures for the α phase (T1) and the α+Si eutectic (T3) has changed slightly. However, the electric conductivity has been significantly increased on crystallization of the α-phase (P1), the α+Si eutectic (P3), the α+Mg2Si+Si eutectic (PA), and at the end of crystallization process, as compared with the basic silumin (Fig. 7a). Metallographic examinations have shown that the reinforcing particles occur within the formerly modified α+Si eutectic (Fig. 8b). No differences has been found between crystallization of the AK11 matrix composite and the matrix alloy itself (Fig. 7b). Only the temperature of the end of crystallization has increased, reaching the temperature of α+Si eutectic crystallization (Figs 5, 6). This increase has caused a change in morphology of the eutectic silicon in the composite (Fig. 9d). It can be generally stated that the registered crystallization curves t, dt/dτ, σ, and dσ /dτ confirm a catalytic influence of reinforcing particles on the crystallization process of aluminium alloy matrix composites.