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

Particle reinforced aluminum metal matrix coMPosites(AI MMCs),which exhibit excellent combinations of high specific strength,high specific stiffness,low coefficient of thermal expansion and excellent wear resistance,have wide application in aerospace-flight,aviation structure,and heat resistant-wearable parts of engine,and thus represent the mainstream of conteMPorary research and development of metal matrix coMPosites.However,the special microstructure of Al MMCs,which lead to the poor weldability and the difficulty in obtaining high strength welded joint,severely hinder the application of the coMPosites in welded construction.Therefore,a systematic study on the weldability of aluminum matrix coMPosites is imminent.In this paper,SiCp/Al MMCs were selected as research objects,and process and mechanism of SiCp/6061Al MMCs by plasma arc welding(Ar and N2 as ionized gas, Ar as fielded gas) were systematically studied.OM(optics microscopy),SEM(scanning microscopy) and XRD(X-ray diffraction) were used to observe the microstructure and changing of coMPositions of fusion welded joints of coMPosites.Mechanical properties of fusion welded joints were measured by microhardness and tensile tests.CoMPact microstructure without phases of Al₄C₃ was obtained by plasma arc "in-situ" welding of SiCp/6061Al MMCs with Al-Si-Ti-Ni 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 were thus iMProved and the tensile strengths of weld joint reach 226MPa.The test results of mechanical property show that the maximum tensile strength of welded joint gained with Al-Si-Ti-Y alloy as filled coMPosite is 240MPa.the microstractures and mechanical properties of the welding joint were researched analysis by plasma Arc "in-situ" welding of SiCp/6061Al MMCs with Al-Si-Ti-Y alloy fillers.The grains were refined and dense microstractures were gained.In addition,the effects of yttrium element on microstructures and factors influence the mechanical properties were also investigated.The result shows that the rare earth element yttrium can iMprove the strength,plasticity and toughness.The microstractures of weld can be ameliorated,too. 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 500℃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 particles.The grains of heat affected zone were refined during the heat treatment,and were the same as that of base material.Thus the tensile strength of joint was heightened to 255 MPa,and the hardness of the the heat affected zone recovered to the pre-welding value.