Study On Interface Microstructure And Properties Of Solid-liquid Cast 1070A/2024 Aluminum Alloy

Composite materials have excellent properties that are difficult to be possessed by a single material,and have been widely used in construction,military industry,aerospace,power electronics,chemical industry,nuclear power,ships,automobiles and other fields.However,the forming mechanism and composite mechanism of composite materials in the preparation process have not been fully verified and need further study.In this thesis,1070A was used as the coating layer and 2024 aluminum alloy was used as the matrix material,and the bimetallic composite was prepared by solid-liquid casting and rolling composite.The 2024 aluminum alloy had poor corrosion resistance without significantly reducing the strong plasticity.NF6-300two-roll vertical casting and rolling machine was used to adjust different process parameters.Optical microscope,electron microscope,X-ray diffractometer,universal tensile machine and other instruments and equipment were used to explore the diffusion law of elements at the composite interface and the formation mechanism of compounds.The effects of different casting temperature and roll speed on the microstructure and properties of the samples were studied.The results are as follows:When the casting temperature is low,there is crack initiation at the composite interface,and the connection of the two metals mainly relies on mechanical meshing.With the increase of the casting temperature,the two metal elements diffused with each other,and the defects of the composite interface gradually disappeared.The brittle and hard phases such as Al₂Cu and Al₂Cu Mg intermetallic compounds were formed at the interface,and the two metals gradually changed from mechanical meshing to metallurgical bonding.As the temperature continues to rise,the diffusion of elements increases,the generation of brittle and hard phase decreases,and the shear strength decreases first and then increases.The shear strength reaches the highest value of 88.7MPa at the casting temperature of 680℃,and the hardness reaches the highest value of 126.4HV at 690℃and then begins to decline.In the roll speed test,the changes of shear strength and roll speed are similar to that of casting temperature.When the roll speed is 12m/min,the shear strength reaches the highest value of80.71MPa.The interface hardness reaches the highest value of 129.5HV at 10m/min.After annealing at low temperature,the microstructure defects can be eliminated,the residual stress can be reduced,and the composite strength of the two metals can be increased.At 200℃for 3h,the interface morphology and microhardness of the composite change little,and the shear strength increases to 94.5MPa.When the annealing temperature is 300℃,some brittle and hard phases disappear,the microhardness decreases slightly,and the shear strength increases to 103.6MPa.With the increase of annealing temperature,the intermetallic compounds dissolve gradually and the binding lines disappear gradually.When the annealing temperature reaches400℃,the intermetallic compounds disappear almost completely,and the shear strength and microhardness decrease significantly.After annealing at 500℃,a large number of alloying elements migrated,the bonding line disappeared completely,and the mechanical properties decreased.In the experiment of holding time,the shear strength of the sample reached the maximum value of 97.3MPa after annealing at400℃for 2h,and the interfacial hardness decreased significantly after holding time for 3h,while the matrix hardness showed a slow decline trend with the increase of holding time.