JOURNAL OF COMPOSITE MATERIALS Article Synthesis and characterization of zinc oxide reinforced aluminum metal matrix composite produced by microwave sintering Neeraj Kumar Bhoi , Harpreet Singh and Saurabh Pratap Abstract The study focuses on the microstructural, phase transformation, and physical and mechanical aspects of aluminum/zinc oxide composite produced by a hybrid microwave sintering technique. In the present case, zinc oxide nanorods were synthesized through a cost-effective thermal decomposition method. The obtained zinc oxide nanorods’ length was in the range of 76– 168 nm observed through high-resolution transmission electron microscopy images and crystallinity nature was confirmed by the bright spot in the selected area electron diffraction pattern. Two different wt% (i.e. 0.5 and 2) of zinc oxide nanorods were utilized for the fabrication of the composite material. The diffraction pattern of the milled powder and energy dispersive spectroscopy results shows effective diffusion of zinc oxide nanorods in the aluminum. The elemental mapping of milled powder illustrates the uniform distribution of the reinforcement over matrix material. The micro-hardness results exhibit a higher hardness of 27.78% with a small fraction of 2 wt%. The nano-indentation results confirm the improvement in the nano-hardness by 32.21% with 2 wt% of zinc oxide with a marginal decrease in elastic modulus by 4.92%. Keywords Metal matrix composites, microwave sintering, microstructure, X-ray diffraction, micro and nano-hardness, elastic modulus Introduction Development of lightweight materials brings up an advent class of opportunities in the various implemen- tations such as brake drum, piston, bike frame, landing gear applications, space craft, and combat vehicles for defense purposes. 1,2 Ceramic reinforcements like Al 2 O 3 , SiC, BN, TiB 2 , TiC, VC, Si 3 N 4 ,Y 2 O 3 , and similar elem- ents are widely engaged for the enhancement in the strength and modulus of aluminum (Al) since the cer- amics are harder and have superior thermal stability. 3–9 The utilization of whiskers in the form of a different one- and two-dimensional structure enhances the material properties significantly. The whiskers hold good thermal, chemical, structural, and tribological stability over other particles when they are used for reinforcement in the metal matrix. 10 The relation between the grain size and inter-particle spacing between the Al and zinc oxide (ZnO) plays a vital role in the strength contribution. The Hall-Petch relation and Orowan strengthening mechanism effectively coupled and quan- tify with the behaviour of grain size and material property. 11 In this context, Guo et al. reported tetra- pod-like ZnO whiskers in the Al matrix composite material. The tensile strength and hardness values were significantly increased by 66 and 65.18%, respectively, in the axial direction of the developed composite mater- ial. 12 Similar results published by Yue et al. 13 show the tensile strength of the developed composite material improved significantly by the addition of ZnAl 2 O 4 and ZnO coated Al borate whiskers. It is well noted that the material properties can enhance by the incorporation of rigid particles or fibers throughout the structures. The proper choice of the reinforcement material in terms of shape, sizes, and chemical stability plays a vital role during the performance. 2,10,14 Utilization of carbon- based nano material can be seen in Al-based material Department of Mechanical Engineering, PDPM IIITDM Jabalpur, India Corresponding author: Neeraj Kumar Bhoi, PDPM IIITDM Jabalpur, Jabalpur 482005, India. Email: neerajbitd@gmail.com Journal of Composite Materials 0(0) 1–12 ! The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0021998320918646 journals.sagepub.com/home/jcm