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In this study, the joining experiment of SiCp/Al composites with 4 mm thickness was carried out, and the effects of different tool rotational speeds (600, 1000 and 1400 rpm) on the microstructure evolution and mechanical properties of joint were studied. The results show that the rotation speed has a significant impact on the microstructure of the weld nugget (WN). The aluminium matrix forms a fine equiaxed crystal structure in WN. As the rise of the rotational speed from 600 to 1400 rpm, the grain size of WN decreased from 6.9 to 2.3 μm. Compared with the base material, the microhardness of the nugget zone was higher. As the rise of rotational speed, the maximum microhardness value increased. The ultimate tensile strength (UTS) of joints decreased with the increase of rotational speed and can reach 95.9% of the base material at 600 rpm. The failure modes of friction stir welding (FSW) joints are mainly ductile failure and SiC particle fracture. [ABSTRACT FROM AUTHOR]

As a key component of friction stir joining (FSJ), tools play an important role in welding quality and welding performance. In this study, the acoustic emission (AE) signal acquisition system was established. The AE signals from FSJ of SiCp/Al composites were analyzed in the time domain, frequency domain, and time-frequency domain respectively. The root mean square (RMS) value, spectrum distribution, and energy distribution of AE signals during FSJ were obtained. The relationship between the tool wear state and the AE signal was studied. The results show that with the increase of welding times, the wear degree of the pin is aggravating. The more serious the tool was worn, the greater the RMS value of the acoustic emission signal was. With the increase of wear, the energy of AE signals gradually moves to the low-frequency region, and the spectrum tends to be concentrated. According to wavelet packet decomposition of AE signals, it has been found that in the frequency bands 3-8, the energy percentage increases with the aggravation of agitation tool wear, while the opposite trend appears in the frequency bands 10-16. [ABSTRACT FROM AUTHOR]

The hard particles in particle-reinforced aluminum matrix composites significantly increases tool wear during friction stir welding (FSW), resulting in the shortage of tool life. In this study, SiCp/Al composites are used as the research object, and the tool wear experiment in friction stir welding is carried out by using high-speed steel pin and high-speed steel + AlCrN coated pin. A new method for calculating tool wear based on hydrodynamic pressure is proposed, and the tool pin wear prediction model is established and verified by experiments. The results show that the wear rate of AlCrN coated pin is very low at the beginning, indicating that AlCrN coating can extend the tool life to a certain extent. However, the wear rate of the tool will increase significantly after the coating is worn away. Through the analysis of the surface wear morphology of the pin, it is found that the main mechanisms of tool wear in the friction stir welding of SiCp/Al composites are the micro ploughing and micro cutting of SiC particles. • A wear model is established for cylindrical pin during FSW of SiCp/Al composites. • Micro ploughing and Micro cutting are primary wear mechanisms for pin. • The wear characteristics of uncoated pin and AlCrN coated pin are investigated. [ABSTRACT FROM AUTHOR]