Research On Process And Joining Mechanism Of Friction Stir Welding Of CFRP And Aluminum Alloy

Aluminum alloy and carbon fiber reinforced composites are the preferred materials for lightweight industrial products.Connecting them can obtain lightweight structural parts with excellent performance.However,the high-quality and reliable connection between aluminum alloy and carbon fiber reinforced composites is an unsolved problem.At present,the commonly used methods include bonding,mechanical connection and fusion connection,but it is difficult to obtain satisfactory connection quality.In this paper,6061 aluminum alloy and thermoplastic short carbon fiber reinforced composites are used to test the connection method of friction stir welding.The effects of mixing tools and process parameters on weld formation,micro morphology and mechanical properties are studied.The finite element simulation model is established.Combined with joint forming analysis,the connection mechanism between metal and polymer is revealed.Firstly,the process experiment of lapping mode is carried out,and the welding experiments of stirring heads with different needle lengths are designed to compare and analyze the weld surface forming quality of different stirring heads after welding.When the aluminum plate is fixed on the upper side,2mm stirring needle is used for welding,the surface is intact,cracks are generated due to welding stress,and no effective connection is formed;The effective connection was obtained by using 2.5mm and 3mm stirring needles,but there was a large amount of PEEK overflow on the weld surface and the surface formability was poor.When the Carbon Fiber Reinforced PEEK plate is fixed on the upper side and the 2.5mm and 3mm stirring needles are used to match the rotation speed and welding speed,the plastic materials in the nugget area are fully plasticized and flow,so as to obtain a relatively complete weld surface and form an effective connection joint.Secondly,the simulation model of friction stir welding and lap welding of dissimilar materials based on Euler Lagrange method is established,and the quality scaling technology is used to improve the simulation efficiency.The temperature field and cross-sectional material distribution under the welding process are obtained.The comparison with the experimental results proves the reliability of the model.On this basis,the formation of aluminum anchor of aluminum/Carbon Fiber Reinforced PEEK dissimilar material lap joint is studied.Combined with the flow of carbon fiber,the connection mechanism of friction stir lap welding between aluminum and Carbon Fiber Reinforced PEEK is discussed.The results show that the front-end temperature is higher than the back-end temperature during welding.so the forward aluminum anchors are obviously larger than the back aluminum anchors,and the change of stitch length has little influence on the peak temperature of welding.Finally,the formation law of aluminum anchor of aluminum/carbon fiber reinforced composite and its effect on the mechanical properties of friction stir welding seam between aluminum alloy and composite were studied under different welding processes,such as rotating speed 1000-2000 rpm and welding speed 30-150 mm/min.The 2.5mm stirring needle failed to stir the aluminum sufficiently,resulting in fracture;When 3mm stirring needle is used,under the condition of constant welding speed,with the increase of rotating speed,the tensile and shear strength of lap joint first increases and then decreases;When the rotating speed is constant,the tensile strength of the joint decreases with the increase of welding speed,and the influence of welding speed on the joint strength is more prominent.When the rotating speed is 1200 rpm and the welding speed is 30mm/min,the maximum tensile and shear strength is 4.75 MPa.