Study On Process And Joint Microstucture And Properties Of SiC_p/2009Al Metal-Matrix Composites Osciallating Laser Welding With Filler Wire

With the progress and development of modern industry,aluminum matrix composite material is widely used in aerospace,national defense,instruments,confidential machinery and other industries because of its excellent performance.Thanks to the advantages of low raw material and manufacturing cost,SiC particle reinforced aluminium matrix composites(SiC_p/Al MMCs)has becoming new structural material that most potential widely applications due to its excellent specific stiffness,specific strength,thermal conductivity,dimensional stability and wear resistance,corrosion resistance and other excellent physical properties.However,in order to expand application of SiC_p/Al MMCs in engineering,it is necessary to study and overcome the jointing technical challenges of complex structural components.Due to the addition of SiC particles,the welding of SiC_p/Al MMCs not only has the difficulties of traditional aluminum alloy welding,but also has many unique welding problems.In order to solve the problem which brittle compound Al₄C₃is easily formed between matrix Al and reinforced SiC particles at high temperature and lead to poor joint performance,in this paper a new oscillating laser welding with filler wire with reserved butt gap is proposed.The welding process of 30%vol SiC_p/2009Al MMCs with 1.6 mm thickness was carried out by reserving different butt gaps.The microstructure and mechanical properties of the optimized joint were analyzed and tested.The mechanism of butt gaps on joint properties was investigated as well.The results show that for the 30%vol SiC_p/2009Al MMCs with a thickness of 1.6mm,a welding joint without surface porosity,undercut,inclusion and other defects can be obtained by the oscillating laser welding with filler wire with butt gap set to 1.3 mm.The pores in the joint weld are rare and the diameter is smaller than 50.0?m.The dilution rate of the base metal is only 19.28%,and there is no obvious SiC particle aggregation and non-fusion.There is little amount of Al₄C₃ brittle phase near the fusion zone of the joint with 1.3 mm butt gap,and the size of Al₄C₃is submicron and the amount is less than one percent of the Al₄C₃ brittle phase that in the zero butt gap weld joint.Due to the heat concentration in joint weld zone and low melting point of Mg element,under higher heat input during welding,the?(Mg₂Si)strengthening phase in the matrix enters into the weld pool and be destroyed with the newly formed part of?(Mg₂Si)in the molten pool,that lead to the solid solution strengthening effect weakened and thus the microhardness of weld was lower than that of the base metal and become softened zone.The fusion zone is subjected to extrusion which from the melted wire to the both sides of base metal,and the dislocation density increases with the flow of the molten pool which lead to enhanced the interaction of the dislocation motion and increases the resistance and deformation resistance.Meanwhile,by reinforcement of?'(Al₂Cu)and?(Mg₂Si)phase,the fusion zone become the reinforced region with the microhardness is significantly higher than the weld and base metal even can reach to 159.2 HV_0.2.Tensile test results show that the fracture location of the joint is near the fusion line,and the fracture is mainly dimples with river pattern disintegration surface occasionally.The analysis shows that the fracture form is mainly ductile-brittle composite fracture.The average tensile strength,tensile yield strength and average elongation after fracture of the joint are 233.3 MPa,225.5 MPa and 3.1%,which are68.3%,81.9%and 42.9%of the base metal respectively.Since the fracture mechanism is mainly toughness fracture and the joint strength is determined by the tensile yield strength,so it is considered that the joint strength can reach more than 80%of the base metal's.