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

With the development of science and technology, aluminum metal matrix composites are more and more widely applied in aerospace, spaceflight, auto manufacturing, optical instrument and sports goods industry due to their excellent combination properties of high specific strength, high specific stiffness, high elastic modulus, better wear-resistance and high temperature-resisting. But Aluminum metal matrix composites are not applied widely in industry due to its poor weldability. The welding technique is the key to wide industry applicaton for aluminum metal matrix composites. SiCp/Al MMCs have been extensively investigated by the scientific communitiy home and abroad. The investigations show that how to pevent the formation of harmful phase Al₄C₃ is the key of the welding of SiCp/Al MMCs. There are also some defects that debase the mechanical property need to eliminate,such as pores, microfissure, inhomogeneous distribution of reinforcement particles.The effects of alloy elements and arc-ultrasonic on microstructures and mechanical properties of weld in plasma arc "in-situ" welding (Ar and N₂ as ionized gas, Ar as fielded gas)of SiCp/6061Al MMCs are investgated in the present work. The results show that the formation of Al₄C₃ was effectively prohibited, the new weld reinforced by TiN, AlN and TiC was produced in "in-situ" welding for SiCp/6061Al matrix composites with 1.2 mm diameter titanium solid wire as filler. But some welding defects still limit the properties of welded joints, such as bulky phase Al₃Ti, slender needle-like phase AlN, particles segregation and so on. The weld structures of welded joints by plasma arc with arc-ultrasounic refine apparently, phase Al₃Ti become smaller and less, the new particles (TiC, TiN) become smaller and more even in the matrix. Tensile results show that the welded joint with 50KHz arc-ultrasonic is optimal, the maximum is 225MPa, about 70% of that of base metal, riasing about 7% compaered with conventional PAW.The results show that the formation of Al₄C₃ was effectively prohibited and new phase particles AlN, TiN and TiC are small but serious segregation in"in-situ" welding for SiCp/6061Al matrix composites with Al-Ti- Mg flux cored wire as filler. While the Mg content in the wire more than 15%, the plasma arc was instability and the weld was poor; while the Mg content less than 5%, the plasma arc was stability and the weld was excellent. And the strength of joint reached 214 MPa. After imposing 50KHz arc-ultrasonic on plasma arc, new particles AlN, TiN and TiC are smaller and more uniform distribution, and the strength reached 236 MPa that is 73.8% of base metal.Dense microstructure without phases of Al₄C₃ were obtained by plasma Arc "in-situ" welding of SiCp/6061Al MMCs with Al-Ti-Si flux cored wire as filler. And no defects such as pores, fissures and incomplete fusion are observed in the central zone of weld. The tensile strengths of weld joints reached 231MPa. Arc-ultrasound has refined the weld and improved particles distribution. The mechanical properties of weld joints were thus improved and the strengths reached 256MPa which is 80% of base metal.