THE THERMAL SHOCK RESISTANCE OF PARTICULATE- AND SHORT-FIBER REINFORCED CAST ALUMINUM-MATRIX COMPOSITES

摘要

The thermal shock resistance of monolithic Al alloys and Al-matrix composites containing graphite, silicon carbide, and 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, the test specimens were heated and stabilized in air at 375℃, water quenched, and air stabilized. The test specimen were fabricated using gravity casting in permanent molds or 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. Squeeze cast Al-alumina and Al-fly ash composites exhibited the best thermal shock resistance. Among monolithic alloys, squeeze cast Al-12SiCuNiMg alloy exhibited better resistance to cracking than Al-25Si and Al-20SiNi 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.