The isolation coupling device is designed based on the principle of high pass filter circuit, which can achieve isolation and coupling between ac welding power and ultrasonic frequency excitation source. In addition, ac arc ultrasonic vibration is obtained successfully. The plasma arc in situ welding of SiCp/6061Al was performed using two different processes. The first process is that the plasma gas is argon nitrogen mixture and the filler material is flux cored wire (Al-5Ti-5Si); the other process is that the plasma gas is argon and the filler material is flux cored wire (Al-15Ti-3Si). The two joints are respectively enhanced by nitride and Al 3 Ti, which were obtained in these processes. After arc ultrasonic vibrations were imposed on the two welding processes, it was revealed that arc ultrasonic improved the distribution of the new nitride phases and optimised the morphology of Al 3 Ti to improve the mechanical properties of joints that reached 246 and 263 MPa. Fracture analysis showed that the improvement of the mechanical properties resulting from Al 3 Ti is better than that from nitride under the effect of arc ultrasonic.

The precipitation behavior of copper sulfides in strip cast and isothermal heat treated low carbon steel were investigated by SEM and TEM. The copper sulfides were classified as duplex inclusion of oxide and sulfide (OS), plate-like copper sulfide (PS), shell-like copper sulfide (SS), and nano-scale copper sulfide (NS). Based on the experimental results, the formation mechanisms of these copper sulfides, as well as the effects of cooling rate and constituentes of steel on the competitive precipitation between copper sulfide and manganese sulfide were discussed. The effects of coppers sulfides on the mechanical properties as well as the formation of acicular ferrite in steel were also introduced.