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Top1. Introduction
In a couple of decades, the role of aluminum matrix composite is unavoidable in the transport, military and air vehicle sectors owing to its amazing properties and the prospective for weight reduction. Utilization of the composites brings out the lower fuel expenditure, energy consumption, noise and airborne emissions in turn enhance the competitive advantage of the aforesaid sectors (Surappa, 2003; Adalarasan & Santhanakumar,2017). Aluminum nitride (AlN) has covalent bond with hexagonal structure. Further, the AlN has exceptional thermophysical properties, superior interfacial adherence with aluminum matrix, greater thermal conductivity and coefficient of thermal expansion. AlN materials extensively used in gas and electronic package industries, wherever elevated temperatures are associated (Liu et al. 2009). Al-AlN composites are employed in producing microelectronic devices (Lii et al. 2003). AA6061 is a precipitation hardened alloy and possess intermediate strength and corrosion confrontation. Magnesium and silicon are major alloying elements of the AA6061 alloy. It is used in assembly of aircraft structures like wings and fuselages, automotive components and marine applications (Amneesh et al. 2016). Yu et al. (2011) reported a way to synthesize in-situ Al–AlN composite by nitriding a powder mixture of AA6061–2% Mg–1% Sn at 560 °C and found that Al–AlN composite offered better mechanical properties than the monolithic alloy. Ayse et al., (2013) developed AlN-Si-Al composites by pressure less infiltration technique. Their investigation report disclosed that the extreme thermal conductivity and thermal expansion coefficient of the fabricated composite. Fale et al., (2013) proposed a novel method to manufacture the Al-AlN composites by reacting the NH4Cl and CaO with aluminum melt. Kumar & Murugan (2012) fabricated the AA6061-AlN by stir casting process and studied the mechanical properties of the composites under various reinforcement ratios. Result of the experimental work indicates that the AA6061-20% AlN composite has the enhancement of 48% yield strength, 32% ultimate tensile strength, 51% hardness (VHN) and reduction of 54% ductility than the unreinforced AA6061 alloy. Among the various methods to produce the composites, stir casting method has numerous advantages including simple, flexible, inexpensive, appropriateness for mass production and production of multi-face profiled composite parts (Hashim et al. 1999). Akbari et al. (2013) discussed a novel method to fabricate the Al-Al2O3 nano composite by integrating the high energy ball milling cum stir casting process. Further, they described the mechanism for attaining the homogeneous distribution and lower porosity by controlling the stirring speed.
The variation of reinforcement size on mechanical properties is well documented in the literature. Akbari et al. (2013) observed the increment in the hardness, tensile and compressive strength by reducing the Al2O3 size from 50 µm to 20 nm. High degree strengthening effect and grain refinement of nano size Al2O3 into the A356 alloy brings tremendous improvement in the aforesaid mechanical properties. Wasik et al. (2017) also noted the similar enhancement in mechanical properties by declining the size of the SiC particle from 60 µm to 2 µm. Ghods et al. (2015) found that the improvement of flexural strength of Al-AlN composite by declining the reinforcement particle size from 1 µm to 50nm.