Microstructures And Mechanical Properties Of A356/2024 Bimetal Fabricated By Solid-liquid Roll Bonding

At present,the laminated metal composites are widely used in aerospace,transportation and electronic communications.However,the formation and regulation mechanism of the interface of metal laminated composites during the preparation process,the coordination of matrix,reinforcing body,interface and performance in the course of service remains to be solved.In this paper,A356 aluminum alloy is used as coating layer and 2024 aluminum alloy as the substrate for liquid-solid rolling.The distribution of intermetallic compounds at the interface and the formation process of interface are investigated.The formation mechanism and interface structure of the intermetallic compounds are analyzed,and the variations in the characteristics of the interface and the mechanical properties of the interface are revealed.The scanning electron microscopy?SEM?,Optical Microscope?OM?,Energy Disperse Spectroscopy?EDS?and XRD were used to analyze the interface solidification structure,element distribution and interface phase of the A356/2024 aluminum alloy composite layer.The mechanical properties of the composite interface were tested by micro-hardness test and shear test.The results are as follows:The cracks,pores and other defects at the interface of A356/2024 sheet gradually disappeared with the increase of pouring temperature of the liquid metal.The interdiffusion of alloy elements in A356 aluminum alloy and 2024 aluminum alloy was occurred.there was an about 110?m wide diffusion layer near the interface.The elements at the interface were enriched to form hard brittle phases such as Al₂CuMg and CuAl₂ intermetallic compounds?IMCs?at the lower pouring temperature.The hardness near the interface of A356/2024 sheet was at the range of 61.5HV to123.9HV.Therefore,it was obvious that the IMCs at the interface can easily lead to brittle fracture of the composite material.The elements at the interface were uniformly diffused at the both sides under higher pouring temperature,thus the accumulation of elements was blocked.The hardness increased from 63.3HV to 104.5HV at one side of the A356aluminum alloy along the vertical direction of the interface to 2024 aluminum alloy.The results show that the interface bonding favorable.With the increase of pouring temperature,the shear strength gradually increased.The shear strength reached a maximum of 48.4 MPa at 720?.With the preheating temperature of the substrate increasing,the segregation of Si at the interface reduced and the chilling effect weekend under the pouring temperature of 680°C.There is enough time for the crystal nucleus in the alloy melt growing into regular grains on one side of the A356 aluminum alloy,and the regular grains are evenly distributed in the entire field of view.When the preheating temperature reached at 500°C,a transition zone of about 400?m was formed at the interface.With the lowering of temperature,the phases at the interface are mainly composed of?-Al,Al₂CuMg,eutectic Si and CuAl₂.With the increase of pouring temperature,the main phase was gradually disappeared at the interface,and the eutectic Si phase was formed in the transition zone.With the increase of preheating temperature,the hardness of A356 decreases,the hardness in the transition zone,however,is maintained about 65-104HV.It is more conducive to improve the bonding strength by increasing the preheating temperature of the substrate.When the preheating temperature reached at 500°C,the transition zone was appeared at the interface,the shear strength of the joint reached the maximum value of 57.93MPa.When the casting temperature is 680°C,the reduction rate is changed.When the reduction rate reaching 10%,the crystal grains of A356 alloy are not deformed,and they are evenly distributed in the field of view and the bonding line is straight.With the increase of the reduction rate,the crystal grains are significantly deformed and elongated along the direction of the rolling force,thus the eutectic silicon breaks,and the interfacial bonding line becomes wavy.When the reduction rate is small,the Si element has no obvious diffusion.With the increase of reduction rate,Si element gradually accumulates at the interface,and Cu element also begins to segregate toward the interface.At the reduction rate of 50%,the“vacuum zone”of aluminum element appears at the interface.At the interface,the content of Si is much higher than the content of Cu,obvious inter-diffusion occurred and metallurgical bonding was formed at the interface.As the reduction rate increases,the strong shear strength gradually increases,and the shear strength reaches the maximum at the reduction rate of 30%.