Experimental Study On Warm Formability Of Automotive Thermoplastic Carbon Fiber Aluminum-based Metal Laminates

Nowadays,energy conservation,environmental protection,and safety have become issues faced on the development of the automobile industry,and the automotive lightweight research is a key to the above puzzles.Based on this background,a new thermoplastic carbon fiber aluminum based laminates（CFRTP/AL）has been developed and fabricated in this paper,including its process preparation method,mechanical properties and formability at room and warm temperatures have been experimental studied.The main research contents are as follows:Firstly,this paper based on the hot molding process,the surface of aluminum alloy was pretreated by mechanical polishing and phosphoric acid anodization,and the thermoplastic nylon 6 carbon fiber prepreg was dried in an oven at 60°C for 30 min.CFRTP/AL and the corresponding thermoplastic carbon fiber laminates（CFRTP laminates）were fabricated by selecting reasonable processes parameters.The results show that the optimal combination of process parameters is as follows:heating up to 240°C,holding pressure is 3 MPa,and holding time is 30 s.The excellent adhesion interfaces exist between the aluminum alloy and carbon fiber layers,and the prepared CFRTP/AL is suitable for fabricating metal/composite structural part with the basic of stamping processes.Furthermore,the basic mechanical properties of the composite were systematically studied and the optimal lay-up design was determined.The quasi-static tensile and three-point bending tests of CFRTP laminates were carried out,the results show that the tensile strength of[0o]₁₀ CFRTP laminates can reach 1382 MPa,which is 34.5 times than that of[90o]₁₀,and the bending strength can reach 1090 MPa,which is 15.6 times than that of[90o]₁₀,the fiber direction has great influence on the properties of laminates;Based on the principle of constant thickness,the three-point bending and tensile performance tests of CFRTP/AL[X]₅ with different layup angles were further carried out.The results show that the orthogonal lay-up design with 0o/90o/0o/90o/0oof CFRTP/AL has the best mechanical properties,its tensile strength can reach 470 MPa,and its bending strength can reach 393 MPa.Compared to the-45o/90o/0o/90o/45olay-up design,the mechanical properties of CFRTP/AL were improved by136%and 66%respectively,and this structure has excellent symmetry and uniformity.Finally,based on the advanced Digital Image Correlation（DIC）test technology,the formability evaluation tests of CFRTP/AL at room and warm temperature were carried out.Firstly,thermal tensile tests were carried out on CFRTP/AL with orthogonal lay-up design at different temperatures.The results show that the fracture strain of the specimen was increased from 1.55%at room temperature to 9.8%at 240°C,its formability under elevated temperature is effectively improved.Furthermore,the self-developed high-temperature forming limit test equipment was utilized to conduct CFRTP/AL forming limit test,and the corresponding FLDs of the composite at room temperature,120°C and 240°C were obtained respectively.The results show that the formability of CFRTP/AL laminates at room temperature is poor,but with the increasement of forming temperature,the formability is significantly improved.Compared with room temperature stamping,the principal strain of the minimum size specimens at 240°C increase from 3.8%to 14%,that of the intermediate size specimens increase from 3.8%to10%,and that of the full-circle size specimens increase from 4.1%to 13%.The above results demonstrate CFRTP/AL with the orthogonal layup has a better warm stamping formability at240°C,which meets the forming and preparation requirements of advanced automotive integrated metal/composite parts.