Research On Laser Joining And Interface Enhancement Mechanism Of 6061 Aluminum Alloy And CFRTP

Dissimilar lightweight materials joining,as an important way to conserve energy and reduce emission,has been widely used in aerospace,rail transit,automobile and other fields.Due to high specific strength,specific modulus,impact resistance and good processing and molding,carbon fiber reinforced thermoplastic matrix composite(CFRTP)has become a necessary material to achieve lightweight.However,it is difficult to apply a single CFRTP structure because of expensive cost.The joining between light metal and CFRTP is thus of great practical significance.Aluminum alloy has small specific gravity,good thermal conductivity and low cost compared with titanium alloy,high strength steel and other materials.Connecting aluminum alloy and CFRTP can combine their advantages and expand application scope.In order to obtain the high-quality welded joints and explore the combined mechanism of interface,in this paper,the joints for 6061 aluminum alloy and CFRTP were achieved by thermal conduction welding with laser as the heat source.Firstly,the main process parameters including laser power,traveling speed and defocus distance were discussed using single factor control variable method,and the process window was thus determined.Shear test was implemented to calculate the joint strength,and the melting width of CFRTP was measured.The fracture face was then analyzed.The connection mechanism between 6061 aluminium alloy and CFRTP was analyzed.Scanning electron microscope,Fourier infrared spectrometer(FTIR)and X-ray photoelectron spectrometer(XPS)were used to explain the connection mechanism.The maximum shear strength was 23.8MPa when laser power was 1100 W,traveling speed was 5mm/s and defocus distance was +10mm.XPS result showed that no chemical bonding formed during the laser joining,and interface connection mainly depended on the mechanical interlocking between aluminium alloy and CFRTP.Secondly,according to the connection mechanism between 6061 and CFRTP,the joint strength was improved from the mechanical interlocking and chemical bonding perspectives.On the one hand,laser surface texturing was adopted to prepare the micro-texture morphology with grid pattern on the aluminum alloy surface.The effect of micro texture with different pitch distances and depths on improving the interfacial interlock was studied.On the other hand,the nano-porous morphology was made on the aluminum alloy surface by anodic oxidation,and the effect of morphology obtained at different oxidation times on interfacial connection was studied.Results showed these two methods both could effectively improve the joint strength.The maximum shear strength was increased by 4 times than those joints formed from untreated aluminum alloy and CFRTP.Al-C-O chemical bond and Al-C chemical bond in the interface of aluminum alloy and CFRTP were found after anodic oxidation,which proved the presence of chemical reaction.Finally,ABAQUS finite element software was used to simulate the temperature field during laser joining,and the interface temperature fields under different process parameters were investigated.The theoretical melting width of CFRTP was then calculated,which could further guide and assess the experimental results.