Aging Behaviors and Mechanical Properties of SiC/Al-Zn-Mg-Cu Composites
Particulate reinforced aluminum matrix composites are widely used in various industrial fields owing to their high specific strength and modulus,low coefficient of thermal expansion,etc.In gen-eral,because stronger matrix alloys tend to produce stronger composites,composites with high-strength Al-Zn-Mg-Cu alloys as the matrix are paid considerable attention.However,the aging behavior of the SiC/Al-Zn-Mg-Cu composites has not been well understood.In the present work,SiC particles with a vol-ume fraction of 15%reinforced Al-7.5Zn-2.8Mg-1.7Cu(mass fraction,%)composite and corresponding unreinforced alloy were fabricated using the powder metallurgy technique.The effects of the aging time on the hardness,electrical conductivity,and mechanical properties of the composite and corresponding matrix alloy were investigated.The T6 heat treatment process suitable for the composite was proposed.The nanoscale precipitates under different aging conditions were quantitatively analyzed using TEM and HRTEM.The results indicated that the SiC particles exhibited an obvious promoting effect on the aging process of the SiC/Al-Zn-Mg-Cu composite.The composite reached the corresponding maximum hard-ness 14 h earlier than the unreinforced alloy.The maximum hardness(238 HV)of the composite was 29 HV higher than that of the unreinforced alloy.The width of the precipitation-free zone of the composite was similar to that of the unreinforced alloy,but the number of the grain boundary phases in the compos-ite increased.The formation of the grain boundary phases and interfacial reaction products could con-sume alloying elements and reduce the density of precipitated phases in the composite.Based on HR-TEM,SiC particles did not change the aging precipitation sequence(SSS-GP zone-η'-η)of the Al-Zn-Mg-Cu alloy,and the η'phase was the major strengthening phase of the T6-treated SiC/Al-Zn-Mg-Cu composites.
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