Study On Laser Welding Of SiC Particle Reinforced Aluminum Matrix Composite Based On Nano Effect

In this paper,by means of laser welding,55-75%vol.SiCp/6063Al composites used in the T/R module of Phased Array Radar was connected with a series of Al_80-xCu₂₀Ti_x?x=3,5,8,10?alloy prepared by rapid quenching.Not only the nanocrystal structure and its formation mechanism,the laser brazing process and its connection mechanism were analysed as well.Due to the strong interfacial activity and atomic diffusion capacity of the nanocrystal structure,the wettability and filling ability of the filler were improved in the laser brazing process,which had characteristics of fast heating and instant cooling.80%strength of the parent material can be obtained under the optimum welding condition.Though it could be connected the parent material with six different fillers?three micron scale fillers of AlZn25Si1,ZnAl7 and Sn flake,three nano particles of Ag,Al,Sn?,the joint strength could not meet the application in engineering.Compared to micron scale Sn flake,the joint of nano Sn particles achieved higher joint strength,due to the strong atoms activity and diffusion property.In the preparation processes of Al_80-xCu₂₀Ti_x?x=3,5,8,10?alloys,under appropriate preparation conditions-such as 1.5×10^-22 Pa vacuum degree,1.0¹.2 mm jet distance,1000¹100 Rad/min speed of copper roller and 0.04⁰.05MPa injection pressure-the coarse grain structure melting by vacuum arc containing?-Al?CuAl₂ and Al_6.1Cu_1.2Ti_2.7changed to 50²00nm size range CuAl₂ and Al_6.1Cu_1.2Ti_2.7 particles.The wettability tested in vacuum brazing furnace showed that foil liquidus increased with Ti content increasing,resulting in the wetting effect decreased and the metallurgical reaction intensified.The main products are Mg₂Si phase,TiSi phase and TiC phase around SiC particles.In the laser welding process of lap joint and butt joint,line energy input determined the seam forming.Better joint forming can be obtained through suitable laser power,defocusing distance and welding speed.In lap joint,the maximum shear strength was 217MPa?80.4%of the parent material?with Al₇₅Cu₂₀Ti₅ filler and the relevant parameters:laser power was 520W,defocus distance was-1mm and welding speed was 1.5cm/s.In butt joint,the maximum tensile strength was 219MPa?81.1%of the parent material?with Al72Cu20Ti8 filler and the relevant parameters:laser power was 350W,defocus distance was-1mm and welding speed was 1.5cm/s.In both lap and butt joint laser brazing process with AlCuTi foil,the microstructure could be divided into columnar crystal region,fusion transition zone and base metal part.It is determined by the laser welding characteristics of rapid melting and instantaneous solidifying.Complex chemical reactions existed in the brazing seam,including?-Al as the main base phase,particle phase SiC and TiC,Mg₂Si distributing in the columnar crystal region,TiCu₄,TiSi and CuAl₂ intermetallic compounds.At last,Al-Si-Fe and Al4C3 in the brazing seam were harmful for both lap and butt joints.Testing by high magnification SEM and TEM for the interface of SiC particles in brazing seam,two kinds of interface?SiC-Al and SiC-TiC?were analyzed.The former interface was mainly direct electron bonding and accelerated diffusion through the micro-reaction between Al and SiC,and the latter was depending on chemical reaction between Ti and SiC,whose main products were TiC and Ti5Si3.The analyses of shear fracture and tensile fracture showed brittle fracture in the joint and only little plastic deformation in the Al base matrix.The step-shape part on the SiC particles in the fracture surface illustrated that SiC particles were the main load carrier in the joint.So the brazing seam enhancement mechanism is particle bearing stress mechanism.Compared to micron scale AlCuTi filler in the wetting test and laser brazing process,the amorphous/nanocrystalline structure,due to its stronger activity and higher atomic movement ability,could improve the brazing seam composition uniformity,increase the infiltration and flow ability of the filler metal,finally enhance the filler elements'diffusion ability of the Al-MMCs matrix.