THE EFFECTS OF Zr ADDITION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A356–SiC COMPOSITES C. Panthglin, S. Boontein, and C. Limmaneevichitr Department of Production Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand J. Kajornchaiyakul National Metal and Material Technology Center, National Science and Technology Development Agency, Pathum Thani, Thailand Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00439-w Abstract The influences of Zr on the microstructure of A356–15 vol% SiC composites, such as the distribution of SiC par- ticles in the matrix, the grain size and the hardness and impression creep between 225 and 275 °C, were examined. These composites were prepared using the stir casting technique. The addition of Zr forms Al 3 Zr phases, which can act as heterogeneous nucleation sites, thus resulting in grain refinement. Furthermore, Zr leads to a more uniform distribution and an increased area fraction of SiC parti- cles. Moreover, the addition of only 0.1 wt% Zr signifi- cantly increased the Brinell hardness by approximately 18% when compared to the composite without added Zr. The addition of a small amount of Zr (0.1 wt%) is sufficient to increase the Vickers microhardness by approximately 34% when compared to the composite without added Zr, indicating the effect of solid solution strengthening on the composite matrix. The high-temperature stability test using the impression creep technique demonstrated that the A356–15 vol% SiC composite with 0.1 wt% added Zr shows improved creep resistance. However, the creep resistance of composite samples with higher than 0.1 wt% added Zr decreases due to grain boundary sliding occur- ring in the A356–15vol% SiC composites with too much added Zr. Keywords: A356–SiC composites, zirconium, grain refinement, impression creep Introduction Aluminum matrix composites (AMCs) reinforced with SiC particles are increasingly being used as engineering mate- rials for many applications including automotive, aero- space and nuclear industries because these reinforced composites are lightweight, have a low coefficient of thermal expansion, have high specific strength and stiff- ness, and have improved wear resistance and hardness. Many studies on A356–SiC composites are being con- ducted to implement these composites in applications such as pistons, crank cases, disk brakes, drum brakes, con- necting rods and bicycle frames. 1–4 AMCs are produced using a variety of methods such as stir casting, powder metallurgy, infiltration and spray deposition. 1–5 For the production of most AMC composites, the stir casting technique is one of the simplest and most economical processes for fabricating the particulate metal matrix of these composites. 6,7 Many studies on AMCs focus on improving the volume fraction and distribution of ceramic particles in the alu- minum matrix, which leads to improvements in both the mechanical properties of the composite and the reliability of the production process. Hashim et al. 7 showed that in the solidification processing of AMCs, the wettability is par- ticularly important to create a strong interface between the ceramic reinforcement particles and the aluminum matrix. Thus, the wettability also plays a critical role in deter- mining the mechanical properties of AMCs. Hashim et al. 7 and Rezayat et al. 8 found that the addition of alloying elements such as Mg, Ca, Ti and Zr to the aluminum matrix can potentially improve the wettability of the ceramic reinforcement particles and the metal matrix. Mg is well International Journal of Metalcasting/Volume 15, Issue 1, 2021 169