| Particle reinforced aluminum matrix composites have outstanding advantages such as low density,high modulus,high specific strength/stiffness,wear resistance,and excellent thermal stability,as well as excellent plastic processing ability and isotropy.They.have become an important development direction for lightweight metal structural materials.In recent years,with the acceleration of the lightweight process in the fields of aerospace and rail transit,the application of aluminum matrix composites and lightweight metals such as aluminum alloys and magnesium alloys has been increasing year by year.Therefore,how to achieve high-quality connections between dissimilar metals has become a key technical problem that needs to be urgently solved in the industry.At present,plastic forming processes represented by composite extrusion and laminated rolling have gradually been applied to the connection and forming of dissimilar metals.Among them,the porthole die co-extrusion forming process not only has the advantages of no pre-treatment on the surface of the billet and short processing process,but also provides a high-temperature,high-pressure,and near vacuum environment for the metal billet in the welding chamber,thereby avoiding oxidation and significantly improving the solid-state welding degree of dissimilar metals.This article focuses on aluminum matrix composites,aluminum alloys,and magnesium alloys,and designs a bimetallic shunt coextrusion mold and experimental device.The feasibility of connecting aluminum matrix composites with aluminum alloys and magnesium alloys using the shunt coextrusion process is verified.The effects of extrusion temperature,extrusion speed,composite profile combination method,Si3N4 particle content,and subsequent hot pressing treatment on the interface connection quality of bimetallic composite profiles are studied The influence of microstructure and mechanical properties.The main content and conclusions of this article are as follows:(1)Under different extrusion temperature conditions,bimetallic composite extruded profiles of Si3N4/Al composite material and 1060,6063,and 7A99 aluminum alloy were prepared using the porthole die co-extrusion process.The welding interface structure,grain morphology,and microstructure of the composite profiles were analyzed,and the influence of extrusion temperature on the microstructure and mechanical properties was studied.The results show that the welding quality of the connection interface between Si3N4/Al composite material and different grades of aluminum alloy is good.The Si3N4/Al composite material undergoes dynamic recrystallization during the extrusion process,and both the grain size and recrystallization fraction increase with the increase of extrusion temperature.The introduction of Si3N4 particles induces the particle excitation nucleation mechanism,thereby promoting the occurrence of dynamic recrystallization.1060 and 7A99 aluminum alloys experienced a high degree of dynamic recrystallization,while 6063 aluminum alloy experienced abnormal grain growth.In addition,there are strong rolling textures and some weak recrystallization textures on both sides of the welding interface in the composite profile.The ultimate tensile strength of Si3N4/Al composite material and 1060 aluminum alloy composite profile is the lowest,but the elongation is the highest;,However,when welded with 7A99 aluminum alloy,it shows the opposite trend.(2)A three-layer composite profile of Si3N4/7075Al composite material and 6063 aluminum alloy was prepared based on the porthole die co-extrusion and subsequent hot pressing processes.The effects of extrusion speed and hot pressing temperature on the welding interface,microstructure evolution,and mechanical properties of the composite profile were studied.The results indicate that the Si3N4 particles shift towards the[1-21-3]band axis during the porthole die co-extrusion,promoting the generation of dislocations in the aluminum matrix near the particles.Mg,Zn,and Cu undergo slight segregation at the Si3N4/7075Al interface.The extruded Si3N4/7075Al composite material mainly contains deformed grains and a small amount of fine equiaxed grains.After hot pressing,the grains are significantly elongated,and dynamic recrystallization is strengthened.The 6063 aluminum alloy exhibits interphase distribution of strip-shaped coarse grains and fine equiaxed grains,and there are a large of small angle grain boundaries distributed inside the coarse grains.After hot pressing,the proportion of fine equiaxed grains and small angle grain boundaries further increases.In extruded composite profiles,Si3N4/7075Al mainly contains rolling textures such as R-Copper and Brass,while 7075 aluminum alloy also contains certain R-Cube recrystallization textures in addition to rolling textures such as R-Copper and Brass.After hot pressing,the strength of these textures is significantly increased.The tensile fracture first occurred in Si3N4/7075Al composite material,followed by the fracture of 6063 aluminum alloy.When Si3N4/7075Al is used as the intermediate layer,the composite profile has a good fracture elongation;When Si3N4/7075Al is used as the surface layer,the composite profile has higher tensile strength.With the increase of hot pressing temperature,the tensile properties of composite profiles are improved to some extent.(3)A three-layer composite profile with Si3N4/6061Al as the surface layer and AZ31 magnesium alloy as the intermediate layer was prepared based on the porthole die coextrusion and subsequent hot pressing processes.The effects of Si3N4 particle content and hot pressing temperature on the microstructure and mechanical behavior of the composite profile were studied.The results indicate that a diffusion zone with a double sublayer structure is formed at the bimetallic interface,and its width increases with the increase of hot pressing temperature.The Si3N4/6061Al composite material is mainly composed of coarse elongated grains and a small amount of fine equiaxed grains.After hot pressing,the fraction of dynamic recrystallization is strengthened,and the high content of Si3N4 particles further promotes the occurrence of dynamic recrystallization;The AZ31 magnesium alloy near the welding interface exhibits coarse deformed grains,while the grains far from the interface are mainly equiaxed.After hot pressing,AZ31 magnesium alloy exhibits coarse grains with TD//<0001>orientation and a small amount of equiaxed grains with interphase distribution,resulting in a significant reduction in grain size.The extruded Si3N4/6061Al composite material mainly contains rolling textures such as Copper and Brass,and recrystallization textures such as Cube appear after hot pressing.The extruded AZ31 magnesium alloy exhibits strong {0001} basal texture,and the texture strength increases after hot pressing.During the stretching process of composite profiles,cracks first occur at the bimetallic connection interface,followed by the fracture of AZ31 magnesium alloy,and the final fracture of the outer layer Si3N4/6061Al.The increase in Si3N4 particle content and hot pressing temperature will affect the mechanical properties of composite profiles. |
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