Research On The Technology Of Plasma Arc "In-situ" Welding Of SiC_p/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 is not applied widely in industry duo 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 is also some defects that debase the mechanical property need to eliminate,such as pores, pores microfissure,inhomogeneous distribution of wild phase.The effects of alloy elements and heat treatment on microstructures and mechanical properties of weld in plasma arc "in-situ" welding(Ar and N₂ as ionized gas, Ar as ridded gas)of SiCp/6061Al MMCs and mechanism of its alloying process is investgated in the present work.The changes of microstructure and composition of fusion welded joints of composites was in observation with OM(optics microscopy),SEM(scanning microscopy)and XRD(X-ray diffraction).And mechanical properties of fusion welded joints were measured by microhardness and tensile tests.The results show that there were a lot of needle-like reaction phase Al₄C₃ and also many defects such as gas pores,crack in the weld,which decreased the tensile strength and general properties.And the formation of Al₄C₃ was effectively prohibited,the new weld reinforced by TiN and TiC was produced in "in-situ" welding for SiCp/6061Al matrix composites with 0.8mm thick titanium plate as filler.The mechanical testing results show that the tensile strengths of weld joint with 0.8 mm thick titanium is 203MPa,which is increased by 75%than that without filler.Dense microstructure without phases of Al₄C₃ was obtained by plasma Arc "in-situ" welding of SiCp/6061Al MMCs with Ti-Al,Ti-Al-Si and Al-Ti-Ni-Si alloy filler,whose mass fraction of titanium is 5%.And no defects of pores,fissures and incomplete fusion is observed in the central zone of weld.The mechanical properties of weld joint was thus improved and the tensile strengths of weld joint reach 220MPa.The results show that the optimum heat treatment process of the weld joint by plasma Arc "in-situ" welding of SiCp/6061Al MMCs is T6 solution and aging.The microstructure of heat treated weld was well improved with the size of massive bulky phases Al₃Ti turning into short rod-like,intergranular segregation eliminated and more homogeneous partiles.The grains of heat affected zone were refined during the heat treatment,and were the same with that of base metal.Thus the tensile strength of joint was hightened to 245 Mpa,and its hardness recovered to the pre-welding value.