Study On Preparation Process And Forming Mechanism Of Near Net Shaped Fe-Al Metal-Intermetallic-Laminate Composites

Intermetallic compounds have high elastic modulus,good electrical and thermal conductivity,excellent high temperature structural properties,outstanding oxidation resistance and abrasion resistance,and sulfur corrosion resistance comparable to stainless steel,which are defined as a new type of high temperature structural material between high temperature alloys and ceramics.This kind of material have broad application prospects in many fields,such as aerospace,electromagnetic components,automotive industry,high temperature devices,energy conversion and filtration systems."Made in China 2025" lists intermetallic materials with integrated structure and function as a key development direction.This paper is funded by the National Natural Science Foundation of China(NSFC)project "Fundamental research on laminated Fe/Fe-Al intermetallic composites prepared by near-net-shape forming technology(No:51874087)".The laminated bionic design with shell structure features is used for reference.The controllable preparation technology of micron-level layered composite structure is adopted.The preparation technology and forming mechanism of high-performance and low-cost Fe-Al metal-intermetallic-laminate(MIL)composites are studied.This paper is devoted to the preparation of Fe-Al metal-intermetallic-laminate composites with flat plate shape,flat interlayer and good interface bonding by short process and low energy consumption.The process flow of "Material pretreatment—Hot roll-bonding—Cold rollthinning—Heat treatment alloying" is put forward.The ABAQUS finite element simulation is used to optimize the process parameters of hot roll-bonding process.The microstructure and mechanical properties of the composite interface at various stages are characterized and analyzed.The main research results of this paper are as follows:(1)The process parameters are optimized by simulating the hot roll-bonding process.The main results are as follows:(a)The optimal reduction rate is set to 40%;(b)The critical thickness ratio of the two components is set to 1:0.30;(c)The increase in the number of material layers has no significant effect on the flatness of the plate and the flatness between layers;(d)The fracture mechanism of Fe foil is analyzed.The main reason is that the plastic deformation capacity of the two components is quite different,and the total strain in the non-uniform plastic deformation section of the Al layer is larger than that of the Fe layer.The greater the deformation heat generated by rolling at high reduction rate,the greater the total strain of the Al layer.When the reduction rate is constant,the thick ratio of the Al layer is larger,and the total amount of strain is larger.The Fe layer is in tension,the Al layer is in compression,and the work hardening of the Fe layer is more serious,which makes the Fe layer fracture,while the Al layer is still in the state of necking.(2)Optimized material preparation process:The pretreatment of Fe-Al laminates with the critical thickness ratio above is kept at 420? for 15 minutes,followed by hot roll-bonding at the optimal reduction rate.After hot roll-bonding,the intermediate annealing is performed,and the annealing system is kept at 400? for 1.5h.When the reduction rate of cold rolling reaches 50%,the stress relief annealing is performed,and the annealing system is kept at 400? for 4h.Multiple passes and small reduction are used to reduce the thickness to the target thickness.The expected Fe-Al metal-intermetallic-laminate composites can be prepared by the solid-solid alloying of the thinned sample at 600? for 4h.(3)The formation and evolution mechanism of the intermetallics at the composite interface are as follows:The composite interface is first nucleated,and the two elements diffuse along the interface.In the early stage of diffusion,the interface is even,and in the later stage,the interface has a tongue-like appearance.After the reaction,Fe and MIL are closely embedded and bonding firmly.The phase of the intermetallic compound layer is composed of a large amount of Fe2Al5 and a small amount of Fe3Al,FeAl,FeAl2,FeAl3.(4)The mechanical properties of Fe-Al micro-laminated composites under different conditions are tested.Above the critical thickness ratio.Before alloying,the bending strength of the sample is 1050MPa,the opening angle is 70°,the tensile strength is 600MPa,and the fracture elongation is 5.5%;After alloying,the bending strength of the sample is 350MPa,the opening angle is 70°,the tensile strength is 220MPa,and the fracture elongation is 11.5%;Under the same conditions,the properties of the samples are higher than those of the samples below the critical thickness ratio.According to the fracture morphology observation,the ductile layer(Fe layer)is ductile fracture,and the strong layer(MIL layer)is brittle fracture.