Investigate on the phase interfaces and performance evaluation of TiB2p/Al–Si–Cu–Zn (T6) composites

In this paper, the microstructures, mechanical properties, and corrosion behavior of xTiB2/Al–9Si–3Cu-0.8Zn composites after T6 heat treatment were invested in detail through the combination of different technologies, including optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing, corrosion testing, etc. The research results showed that the average size of the α-Al grains gradually decreased with the increase of TiB2 particles (TiB2p) content. In addition, there was a semi-coherent relationship between TiB2p and the α-Al matrix, and the nanoscale precipitates were identified as θ and θʹ phases by virtue of their crystal orientation relationship. Tensile testing results revealed that an increase in TiB2 content caused the elastic modulus, yield strength and tensile strength of the composites to increase and then decrease. And with a TiB2p content of 4 wt%, they reached 85.7 GPa, 360 MPa and 398 MPa, reflecting increases of 26.2%, 60.0%, and 30.9%, respectively. The contributions of thermal mismatch, grain boundary and Orowan strengthening mechanisms to the overall yield strength of the 4%TiB2/Al–9Si–3Cu–0.8Zn composite were 72.1, 3.8, and 35.6 MPa, respectively. Unfortunately, the corrosion resistance of xTiB2/Al–9Si–3Cu–0.8Zn composites gradually decreased with increasing TiB2p content. The corrosion morphology analysis indicated that the agglomeration of TiB2p and Si weakened the protection afforded by the oxide film, evolving into a point of nucleation for the subsequent corrosion reaction. Moreover, point–pair correlation was observed between the TiB2p and Al matrix, exacerbating the corrosion. The results implied that extra factors be considered in industrial application of TiB2 ceramic particles in a metallic system.