EFFECT OF ALTERNATIVE HEAT-TREATMENT PARAMETERS ON THE AGING BEHAVIOR OF SHORT-FIBER-REINFORCED 2124 Al COMPOSITES

Abstract

The 2124 Al alloy and a composite of the 2124 Al alloy reinforced with 20 % of volume fractions of delta-Al2O3 short fibers made by squeeze casting were subjected to controlled and systematic aging treatments. The materials were solution treated at (495, 525 and 555) degrees C. After quenching, the matrix alloy and the composite were artificially aged at (160, 170, 180 and 190) degrees C up to 36 h. The aging was monitored with hardness measurements and differential scanning calorimetry. The time required to reach the peak hardness of the composite matrix during a precipitation treatment was shorter than that for the unreinforced 2124 Al. An increase in the solution-treatment temperature resulted in an increase of the composite-matrix hardness. The delta-Al2O3-reinforced composite exhibits no grain-boundary melting, but appears to show incipient melting around short alumina fiber interfaces at temperatures above 525 degrees C. The highest HV value was obtained after solutionizing at 495 degrees C for 6 h, followed by water quenching and aging at 190 degrees C for 10 h for the unreinforced matrix alloy. In the case of the reinforced alloy the highest HV value was found after solutionizing at 555 degrees C for 6 h, quenching and aging at 170 degrees C for 12 h.