Aging response of Al-Zn-Mg-Cu spray formed alloys and their metal matrix composites

The aging response of various Al-Zn-Mg-Cu alloys was compared with the reinforced counterpart. The effects of aging temperature and time on the mechanical properties of these alloys, was also determined. Moreover, the effects of quenching rate from solution temperature, time between quench and aging, and heating rate to precipitation temperature were investigated. The study was executed by selecting two different heat treatments for each of three different aging temperatures: one without prior straining, and the other with 2% straining prior to aging to relieve stress. Room temperature tensile testing was conducted to determine these variations of aging on the strength of the spray formed Al-Zn-Mg-Cu alloys. The presence of SiC particles accelerated the aging kinetics of the alloys compared to the unreinforced counterparts. This difference in time to peak aging decreased with decreasing aging temperature. At uniform temperatures, differences for time to peak aging between unreinforced and composite alloys also existed in both the prestrained and unstrained condition. The difference was not as great in the prestrained state. The tensile strengths increased slightly with prestraining, but not significantly. Alloys containing silver maintained high strengths over silver-free counterparts when rapidly heated to precipitation temperatures above 120 degrees C. At slow heating rates, however, the silver-free alloys matched or were slightly higher than the strength of silver alloys, with increasing heating rate. (c) 2006 Elsevier B.V. All rights reserved.