Research On The Technology Of AC Arc-ultrasonic Plasma Arc "In-situ" Welding Of SiCp/6061Al MMCs

Aluminum matrix composites are more economic than other composites in manufacture, easy to popularize and apply due to their low density, high specific strength and stiffness, high shearing strength, low coefficient of thermal expansion, heat stability, excellent conducting heat and current, better wear resistance and corrosion resistance. So aluminum matrix composites are paied more attention as an advanced material. But the poor weldability of alimunim marix composites due to the huge difference between matrix and particles in physics and chemistry is their biggest barrier in widely industrialized appliance. The welding of aluminum matrix composites has been extensively investigated by the scientific communitiy home and abroad. Now, it has been consensus to pevent interface reaction between matrix and particles by using multi-alloying metal including titanium as filler.In this work, SiCp/6061A1 MMCs were joined by plasma arc welding using two processes:the joints reinforced by newborn AIN and TiN were obtained in process (1) (plasma gas:mixture of argon and nitrogen, filler material:Al-5Ti-3Si wire); the joints reinforced by new Al3Ti were obtained in process (2) (plasma gas:argon, filler material: Al-15Ti-5Si wire). An isolation-coupling device based on high-pass filter was designed in order to electrically isolate the ultrasonic source and AC welding power. Then'in-situ' weld-alloying/plasma arc welding with the arc-ultrasonic technology was utilized to join a SiCp/6061A1 MMC. Changing the excitation frequency and voltage, the effects of arc-ultrasonic on welding of SiCp/6061A1 were investaged.Result shows that the morphotogy of newborn Al3Ti change from strip to block, and the number of AIN raise and distribute more uniformly with the increasing of arc-ultrasonic frequency in process (1) with different frequency arc-ultrasonic. The joints with excellent microstructure and tensile strength are obtained when the frequency of arc-ultrasonic is 60 KHz. The biggest tensile strength is 246MPa, increasing 10% than without arc-ultrasonic. In process (2) with arc-ultrasonic, Al3Ti is smaller. The morphotogy of Al3Ti is particle and uniformly distributed when the frequency of are-ultrasonic is 30 KHz,50 KHz and 60 KHz. However, when the frequency of are-ultrasonic is 20 KHz,40 KHz and 70 KHz, Al3Ti distribute in line. The microstructure and strength of joints are excellent when the frequency of arc-ultrasonic is 60 KHz, the biggest tensile strength is 263MPa, increasing about 20% than without arc-ultrasonic.Using process (1) with different excitation voltage arc-ultrasonic, result shows that with increasing excitation voltage the morphotogy of Al3Ti in weld change from strip to particle and distribute more uniformly. The biggest tensile strength is 246MPa when the excitation voltage of arc-ultrasonic is 40V, increasing 10% than without arc-ultrasonic. In process (2) with different excitation voltage arc-ultrasonic, the number of Al3Ti in weld reduces and tends to reunion, the morphotogy of Al3Ti respectively is block, slender-needle, short-rod and short-rod with bifurcation with the reducment of excitation voltage. In addition, the distribution of TiC particles tends to uniform and local position change from interface to inside of grain with the reducment of excitation voltage. The microstructure and strength of joints are excellent when the voltage of arc-ultrasonic is 40V, the biggest tensile strength is 263MPa, reaching to 82% of the tensile strength of base metal.