Abstract
In metal matrix composite (MMC) materials, the reaction between the metal matrix and reinforcement particles could change the composition of the matrix and the interface and lead to interfacial compounds. These intermetallic compounds may have either a deleterious effect to the mechanical properties or beneficial effect in enhancing the toughness and ductility of the composite. An aluminium 6092 alloy with 17.5% volume fraction silicon carbide (SiC) particles sheet manufactured by means of powder metallurgical method, heat treated to T6 condition, is used to obtain a fundamental understanding of the heat treatment effect on the fracture mechanism, the microstructural changes and the interface between the Al-matrix and SiC particles. Changes in the microstructure of the Al/SiCp and the topography of the fracture are investigated using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) to characterize the precipitate and intermetallic compounds formed at the Al/Sic interface. X-ray diffraction (XRD) is utilized to characterize the phase formation and to give confidence in the results of TEM and EDS. Tensile tests with different strain rates (8 × 10−5, 8 × 10−4, 8 × 10−3, 8 × 10−2 and 0.16 s−1) were carried out to study the toughness and to find a correlation between the strain rate and heat treatment. Under T6 condition, the results show that the mechanical property of this MMC is less ductile due to the formation of precipitations as a result of either the interaction between the Al and SiCp or from hardening precipitation treatment, e.g. Al2Cu, Al4Cu2Mg8Si7 and MgAl2. O-condition annealing can reduce the detrimental effect of the intermetallic compounds in the interface region and improve the toughness and ductility of the material by decreasing the intermetallic compound (Al2Cu). However, the Al/SiC sheet treated with O-condition annealing is more sensitive to the strain rate than the one treated with T6.
Highlights
A metal matrix composite (MMC) material is composed of a ductile metal matrix reinforced with a ceramic such as silicon carbide or graphite [1]
The microstructure of the 6092/SiCp composite was investigated in as-received (T6 heat treatment) and O-condition annealing using XL30 scanning electron microscopy (SEM) with a linked energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD)
6092/SiCp composite with T6 heat treatment is shown in Fig. 4; from this figure, it can be seen that there are three distinct regions clearly marked on the backscattered electron (BSE) image, which are Al matrix, the silicon carbide (SiC) particles and inclusion
Summary
A MMC material is composed of a ductile metal matrix (e.g. aluminium or titanium) reinforced with a ceramic such as silicon carbide or graphite [1]. The silicon carbide, as a fibre or particle reinforced Al matrix composite (Al/SiC), can be considered the most favourable type of MMC [5]. The reinforcement of SiC particles is used to enhance the strength and stiffness of Al-alloys, and T6 treatment is utilized to increase the strength of Al-alloy via the formation of precipitations in the Al-matrix. The purpose of the present investigation is twofold; the first is to characterize the phases and intermetallic compounds formed due to interaction between the Al-matrix and SiC particles or from the hardening precipitation treatment, when O-condition annealing is used to reduce the detrimental effect of these compounds by dissolving or refining them so as to improve its ductility. Tensile tests with different strain rates were conducted to study the influence of the strain rate on the mechanical properties and fracture behaviour and to find a correlation between the fracture mechanism under tensile loading and the type of heat treatment as well as to illustrate the effect of the precipitations on the fracture toughness
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