Experimental investigations of heat generation and microstructure evolution during friction stir processing of SnSbCu alloy

The paper presents the results of experimental investigations of the heat generation and microstructure evolution during the friction stir processing (FSP) of the SnSb11Cu6 alloy. The Triflute tool was used for modification; the process was carried out using two rotational speeds of the tool: 280 and 560 RPM and a constant linear speed of 355 mm/min. Microstructure studies were performed employing the techniques of light microscopy and scanning electron microscopy along with analysis of the chemical composition of micro-areas. Additionally, the phase composition was investigated by means of the X-ray diffraction method, and electron backscatter diffraction (EBSD) analysis and hardness testing were performed before and after FSP modification. Furthermore, measurements of the temperature directly on the modified surface by means of a thermal imaging camera and the temperature in the modified zone with a thermocouple system were performed. It was proved that using FSP to modify the SnSbCu alloy promotes refinement and homogenization of the microstructure, as well as improvement of the hardness. The hardness of the starting material was 24 HB, and after FSP, the hardness increased and amounted to, respectively, 25 and 27 HB after processing at 280 and 560 RPM. The microstructure in the stir zone is formed by the dynamic recrystallization (DRX) process and consists of almost equiaxed tin-rich matrix grains with a size of approx. 5–30 µm and fine particles of Cu 6 Sn 5 and SnSb phases. The temperature distribution in the FSP zone is not uniform and changes in a gradient manner.