High modulus Al[sbnd]Si[sbnd]Mg[sbnd]Cu/Mg2Si[sbnd]TiB2 hybrid nanocomposite: Microstructural characteristics and micromechanics-based analysis

Abstract

As an intrinsic materials property and an important criterion in structural design, the Young's modulus of cast aluminium alloys can be significantly increased through adding Si and Cu elements as well as in-situ forming Mg2Si and TiB2 particles in the alloys to make castings with complex geometry. The microstructural evaluation and mechanical properties of AlSiMg alloy and AlSiMgCu/Mg2SiTiB2 hybrid composite were examined by X-ray diffractometer (XRD), optical microscopy (OM), scanning and high resolution transmission electron microscopes (SEM and HRTEM), ultrasonic pulse technique and tensile test. The results revealed that the AlSiMgCu/Mg2SiTiB2 hybrid nanocomposite could provide the Young's modulus more than 94 GPa and the yield strength up to 235 MPa by forming the α-Al (Cu, Mg), Si, Mg2Si and TiB2 phases in the microstructure. Micromechanics-based models were also employed to explain important factors in Young's modulus and yield strength. The theoretical calculation confirmed that the contribution of thermal mismatch, Orowan, elastic mismatch, load bearing and grain boundary strengthening mechanisms to the yield strength are 65.5, 38.3, 26.2, 6.7 and 1.4 MPa, respectively. The AlSiMgCu/Mg2SiTiB2 hybrid composite showed a homogeneous distribution of strengthening phases throughout the aluminium matrix, and a microstructure without any detrimental phases. The interfaces between the aluminium matrix and TiB2 particles were found clean, smooth and well-bonded. And, the TiB2 particles exhibited hexagonal and cubic prism shapes with chamfered edges and corners.