The thermal shock resistance of cast composite materials
* Jerzy Sobczak, * Natalia Sobczak, * Paweł Darłak, ** Dariusz Rudnik, *** Zenon Sławiński, **** Rajiv Asthana, ***** Pradeep K. Rohatgi * Instytut Odlewnictwa, ul. Zakopiańska 73, 30-418 Kraków ** Instytut Transportu Samochodowego, ul. Jagiellońska 80, 03-301 Warszawa *** Politechnika Lubelska, ul. Nadbystrzycka 36, 20-618 Lublin **** University of Wisconsin-Stout, Menomonie, WI 54751 ***** University of Wisconsin-Milwaukee, Milwaukee, WI 53201
Annals 1 No. 2, 2001 pages 219-223
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abstract The thermal shock resistance of monolithic Al alloys and Al-matrix composites containing graphite, silicon carbide, fly ash particulates, and short alumina (Saffil) fibers was characterized by measuring the total length of microcracks as a function of number of thermal cycles (1,000 to 5,000 cycles) of 270 K amplitude. During each cycle (Fig. 1), the test specimens were heated and stabilized in air at 375°C, water quenched, and air stabilized (Fig. 2). The test specimen were fabricated using gravity casting in permanent molds and by squeeze casting, followed by heat treatment (T6) prior to thermal cycling. In all specimens, the total crack length increased with increasing number of thermal cycles (Fig. 3). Squeeze cast Al-alumina and Al-fly ash composites (ALFA®) exhibited the best thermal shock resistance (Fig. 4). Among monolithic alloys, squeeze cast Al12SiCuNiMg alloy exhibited better resistance to cracking than Al25Si and Al20SiNi alloys. Conceptual schemes are proposed for crack propagation behaviors in alloys and composites under thermal cycling conditions. Approximate calculations for the thermal shock resistance of composites based on fundamental material properties are found to be consistent with the experimental observations (Fig. 5).