Study On The Fabrication,Microstructure And Property Of Cu/Al Bimetallic(Polymetallic) Composite Material

Bimetallic?polymetallic?composite is a new type of composite material prepared by a certain bonding process,in which two or more matrix metals with different physical,chemical and mechanical properties achieve metallurgical bonding at the interface.As a common bimetallic?polymetallic?composite,Cu/Al bimetallic?polymetallic?composite is widely used in automobile,electric power,heat transfer,communication,decoration and other fields.This study adopts solid-liquid bonding method including sand mold gravity compound casting and metal mold gravity compound casting to produce two different types of Cu/Al bimetallic composites.It studies how the cooling rate and pouring temperature influence the interfacial microstructures and mechanical properties of Cu/Al bimetallic composite material,and the interfacial intermetallic compounds are characterized and identified.It analyzes the reasons for the formation of different interfacial microstructures,and establishes the relationship between interfacial microstructures and the mechanical properties,perfects the solid-liquid bonding mechanism of Cu/Al bimetallic composite material.In view of the fact that the single solid-liquid roll casting process cannot produce Cu/Al composite materials with low thickness ratio?the thickness ratio of Cu<8%?,this study uses the“roll casting+roll bonding”joint bonding process of preparing the low Cu layer thickness ratio Cu/8011/1060?Cu layer thickness ratio is 4.1%?,and Cu/8011/5052?Cu layer thickness ratio is 1.7%?polymetallic composites.It studies the effect of rolling reduction rate and heat treatment temperature on the microstructural evolution and mechanical properties of polymetallic composite materials systematically.The following conclusions can be drawn:The research on Cu/Al bimetallic composites produced by sand mold gravity compound casting shows that the transition zone of Cu/Al bimetallic composite is composed of intermetallic compound layer and remelting zone.At lower cooling rate?0.8?/s¹.0?/s?,the remelting zone is mainly composed of Al-Cu hypoeutectic microstructures;At high cooling rate?1.0?/s¹.8?/s?,remelting zone is mainly composed of Al-Cu hypereutectic microstructures;As the cooling rate reduces from1.8?/s to 0.8?/s,the interface morphology between the remelting zone and Al matrix changes from flat to dendrite shape,and the interface is rich Cu solid solution area,the width of the rich Cu solid solution increases gradually with the decrease of the cooling rate;When the cooling rate is 1.0?/s,Cu/Al bimetallic composite material has the highest shear strength of 33.3 MPa.Based on the analysis of interfacial cooling curve and microstructure observation,the presolidification zone and its dissolution of Cu/Al solid-liquid bonding interface is proposed,which improved the solid-liquid bonding mechanism of Cu/Al bimetallic composite material.The research on Cu/Al bimetallic composites?Ni-plated Cu matrix?produced by metal mold gravity compound casting shows that a solidification platform of??Al?is observed at about 660?from cooling curve.When the pouring temperature or liquid-solid volume ratio?VR?increases,the solidification time of??Al?increases.The solubility of Cu in Al is positively proportional to the solidification time of??Al?phase,and the solubility rate constant of Cu is 1.2142×10^-5 m/s.When pouring temperature is680?,Ni coating occurs partly dissolved,there are some microscopic gaps at the interface,and it fails to form a metallurgical bonding;When pouring temperature increases to 700?or higher,a continuous metallurgical bonding interface is formed,and it contains intermetallic compound layer and[??Al?+Al₂Cu]eutectic microstructure,and the intermetallic compounds are confirmed for Al₄Cu₉,AlCu and Al₂Cu.When pouring temperature is 700?,Ni coating participates in the reaction with the intermetallic compound layer,AlCu?Ni?exists between AlCu and Al₂Cu phase;When pouring temperature increases to 720?,AlCu?Ni?phase disappears;The optimum technological parameters of metal mold gravity compound casting for Cu/Al bimetallic composite is 720?+VR 49.24,and the corresponding shear strength reaches 36 MPa.Shear failure occurs mainly on the hard brittle intermetallic compound layer.High-performance low Cu layer thickness ratio Cu/8011/1060 and Cu/8011/5052polymetallic composites are prepared by“cast rolling+roll bonding”.Cu/8011bimetallic matrix metal materials are first cast-rolled,and then they are combined with1060 Al alloy or 5052 Al alloy by hot roll bonding with a certain thickness.The study of Cu/8011/1060 polymetallic composites shows that the interface between Cu and8011 Al alloy is mainly composed of continuous intermetallic compounds?IMCs?with uneven thickness.The IMCs have been identified as Al₄Cu₉,AlCu and Al₂Cu.During roll bonding process,the IMCs fracture,and the position of the fracture occurs mainly in three parts:transition zone between?-type IMCs and?-type IMCs;inside?-type IMCs and inside?-type IMCs.IMCs fracture is the most likely to happen at the transition zone between?-type IMCs and?-type IMCs;The rolling reduction rate of Cu matrix is always lower than that of the whole composite,but the rolling reduction rate of Al matrix is slightly higher than that of Cu/Al composite.Cu/8011/1060polymetallic composites in the heat treatment state have the best comprehensive tensile properties?the maximum strength plastic product value?when the rolling reduction rate is 47%,and the tensile strength and elongation are 135.7 MPa and 25.5%,respectively.During the process of stretching,there are two different fracture modes for Cu/8011/1060 polymetallic composites:when the rolling reduction rate is 38%⁴3%,the composite shows a graded fracture phenomenon,and the interface of 8011 Al alloy and 1060 Al alloy is separated.When the rolling reduction rate increases to 47%⁶7%,the composite shows an overall fracture phenomenon,the interface between 8011 Al alloy and 1060 Al alloy does not separate,and the Cu matrix shows multiple fractures.It is found that the yield strength and tensile strength of Cu/8011/1060 polymetallic composites in as-rolled state are in good agreement with the calculated and measured values.The theoretical calculation of yield strength and tensile strength of Cu/8011/1060 polymetallic composites in the heat-treated state are both lower than the measured values.After heat treatment,interfacial interdiffusion can promote the improvement of tensile properties of composite materials to some extent.In-situ tensile deformation based on SEM is used to observe the interfacial fracture laws of two different Cu/8011/1060 polymetallic composites.It is found that the fracture first occurs in the interface between IMCs and adjacent matrix or inside the brittle IMCs,and then mainly extends to the Cu matrix,and clefts the Cu matrix to produce fracture,and continuously produces new cracks in the adjacent IMCs.However,the crack occurs passivation in the Al matrix.Due to a large number of grain boundaries hindering dislocation movement in Cu matrix,strain localization and crack propagation are easy to occur.Due to the good plasticity of Al matrix,the crack tip releases the stress concentration by launching dislocations,reduces the driving force of crack growth,and then restricts the crack growth to Al matrix,leading to blunting.The interface of Cu/8011/5052 polymetallic composites has uniform thickness but discontinuous IMCs.After heat treatment,the grain size distribution of 8011 Al alloy is not uniform.The grains of 5052 Al alloy near the interface of 8011 Al alloy are fine with the size of⁶0?m.Cu/8011/5052 polymetallic composites inherite the tensile characteristics of 5052 Al alloy at room temperature,and teeth is found in the uniform deformation area of the engineering stress-strain curve,indicating the occurrence of dynamic strain aging effect.The yield strength and tensile strength of Cu/8011/5052polymetallic composites at room temperature are approximately equal along the rolling direction?RD?and the width direction?WD?,and the elongation is better in the rolling direction than that in the width direction.Tensile fracture on the cross-section observation testifies the composite experiences the 45°single shear fracture.After high temperature tensile test,it is found that tensile strength of Cu/8011/5052polymetallic composites decreases with the increase of temperature,especially when the temperature is over 300?,the tensile strength decreases significantly.When the tensile temperature is below 200?,the composite still has high tensile strength,more than 120 MPa,and has the potential of high temperature use.When the tensile temperature is below 200?,the Cu/8011/5052 polymetallic composites are 45°single shear tensile fracture;When the tensile temperature exceeds 200?,the Cu/8011/5052polymetallic composites exhibit symmetrical shear fracture morphology,the size of fracture turns thinner.The different degrees of fracture are found in the Cu layer,and the fracture spacing increases significantly with the tensile temperature.