Effect of the surface grain refinement on the wear properties of A356/SiC composites

Abstract

Aluminum alloys are very attractive materials and have a wide application area in industry. However, their weak hardness property requires reinforcement and unavoidable use of particulate composite materials. Nevertheless, mechanical properties of the matrix can be important when sliding conditions are concerned especially wear. Therefore, post treatments can be used to obtain superior matrix properties after reinforcing. In this study, A356 aluminum alloy reinforced by using SiC particles with 5%, 10%, 15%, and 20% mass fractions were manufactured via stir casting process. To examine the effect of the grain refinement on the composites’ wear properties, A356/SiC composite samples were deformed with ultrasonic impact treatment for surface nanocrystallization. Optical microscopy (OM) was used to examine the microstructure, while scanning electron microscopy (SEM) was employed to determine the wear mechanism. Hardness tests and x-ray diffraction were also used to investigate the effect of deformation. Results showed that microstructure contains α-Al dendritic arms and eutectics silicon, and that the porosity increases with rising reinforcement fraction. Upon ultrasonic impact treatment, grains in the microstructure are observed to be oriented through impacts, and the increasing reinforcement fraction is seen to reduce the deformed layer thickness. Further, it is seen that peak broadening occurs, and that hardness values increase as a result of strain hardening upon completion of the treatment. Increasing reinforcement is detected to cause decreased hardened layer thickness, in consistent with microstructure examinations. Furthermore, wear tests showed that increasing reinforcement fraction improves the wear resistance, and that applying the treatment decreases the weight loss during wear tests.