Aging Behaviors and Mechanical Properties of SiC/Al-Zn-Mg-Cu Composites
MA Guonan1,2, ZHU Shize1,2, WANG Dong1(), XIAO Bolv1, MA Zongyi1
1Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Cite this article:
MA Guonan, ZHU Shize, WANG Dong, XIAO Bolv, MA Zongyi. Aging Behaviors and Mechanical Properties of SiC/Al-Zn-Mg-Cu Composites. Acta Metall Sin, 2023, 59(12): 1655-1664.
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 general, 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 volume 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 hardness 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 composite increased. The formation of the grain boundary phases and interfacial reaction products could consume alloying elements and reduce the density of precipitated phases in the composite. Based on HRTEM, 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.
Fund: National Key Research and Development Program of China(2017YFB0703104);National Natural Science Foundation of China(51771193);Liaoning Revitalization Talents Program(XLYC2007009)
Fig.1 OM images (a, b) and grain size statistic plots (c, d) of as-extruded Al-7.5Zn-2.8Mg-1.7Cu alloy (a, c) and SiC/Al-7.5Zn-2.8Mg-1.7Cu composite (b, d)
Fig.2 Aging hardness and electrical conductivity curves of the single-stage aged Al-7.5Zn-2.8Mg-1.7Cu alloy (a) and SiC/Al-7.5Zn-2.8Mg-1.7Cu composite (b) at 120oC (IACS—international annealed copper standard)
Fig.3 Tensile properties of Al-7.5Zn-2.8Mg-1.7Cu alloy (a) and SiC/Al-7.5Zn-2.8Mg-1.7Cu composite (b) aged at 120oC for 0, 2, 8, 10, 24, and 48 h (UTS—ultimate tensile strength, YS—yield strength, EL—elongation)
Fig.4 Precipitation morphologies (a-c) and size statistic plots (d-f) of Al-7.5Zn-2.8Mg-1.7Cu alloy under different aging treatment conditions taken along [110]Al zone axis (a, d) under-aged (120oC, 2 h) (b, e) under-aged (120oC, 10 h) (c, f) T6-treated (120oC, 24 h)
Fig.5 Precipitation morphologies (a-c) and size statistic plots (d-f) of SiC/Al-7.5Zn-2.8Mg-1.7Cu composite under different aging treatment conditions taken along [110]Al zone axis (a, d) under-aged (120oC, 2 h) (b, e) under-aged (120oC, 10 h) (c, f) T6-treated (120oC, 24 h)
Fig.6 DSC curves of the solution treated (470oC, 2 h) unreinforced alloy and composite
Peak
Unreinforced alloy
Composite
1
79
79
2
172
-
3
224
218
4
243
240
5
262
262
6
450
438
Table 1 Temperatures of peak points (in Fig.6) in the DSC curves of the solution treated unreinforced alloy and composite
Fig.7 HRTEM images (a-c) of the precipitation in the T6 treated composite taken along [110]Al zone axis, and the fast Fourier transformation (FFT) patterns (d-h) of the marked zone in the HRTEM images in Figs.7a-c
Fig.8 Bright-field TEM images of grain boundaries of the unreinforced alloy (a, b) and the composite (c, d) (a, c) aging 2 h at 120oC (b, d) T6-treated (120oC， 24 h)
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