Study On Microstructure And Mechanical Properties Of Al/Al/Cu Composites Prepared By Accumulative Roll Bonding

Laminated composites are widely used in aerospace,automotive,energy and communication industries because of their excellent comprehensive properties.Al/Al/Cu composites have attracted the attention of many scientists at home and abroad because of their advantages such as low density,good formability,corrosion resistance and excellent electrical and thermal conductivity.Accumulative roll bonding(ARB)can be used to prepare various metal composites because of its low cost and simple operation.In this paper,Al/Al/Cu multilayer composites were successfully prepared by ARB process to improve the strength of the composites.The heterogeneous layered structure,microstructure,mechanical properties and fracture mode of Al/Al/Cu composites were studied by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),electron backscattering diffraction(EBSD),tensile test at room temperature and microhardness test.The fracture mechanism of Al/Al/Cu composites was revealed.ARB0 cycle,ARB1 cycle,ARB3 cycle and ARB5 cycle’s composites were selected for annealing tests.The effects of annealing on the macroscopic structure,microstructure and mechanical properties of the heterogeneous interface of the composites were studied.ARB0,ARB1,ARB3 and ARB5 cycle’s composites were selected for rolling thinning,and the changes of macroscopic interface structure,microstructure,mechanical properties and fracture mode of the composites after one straight rolling and two straight rolling were studied.The main conclusions are as follows:(1)In this paper,Al/Al/Cu composites were prepared by six cycles cumulative rolling(ARB)process using Al4343,Al3003 and Cu sheets as raw materials.In the first two cycles,Al4343,Al3003 and Cu layers maintain layered structure.After three cycles,the Cu layer appears necking,and after four cycles,the macroscopic shear zone appears,which is 30° from the rolling direction.At the same time,necking and local fracture are found in the Cu layer.After 6 cycles,the Cu fragments become smaller and evenly distributed in the(Al)matrix composed of Al4343 and Al3003.In the first three cycles,the Cu grains are refined continuously along the rolling direction.After five cycles,a large number of recrystallized grains appears in the Cu,and the average grain size is750 nm.The tensile results show that the strength of the Al/Al/Cu composite increases first and then decreases,and the elongation decreases continuously.At the third cycle,the strength reaches 625 MPa and the elongation reaches 6.67%.After the 4th cycles of copper fracture,the strength decreases and the elongation continues to decline.After 5and 6 cycles of copper fracture,the strength and elongation change little.The fracture of the composite changes from delamination-necking fracture to shear fracture,and from ductile fracture to tough-brittle mixed fracture.(2)After annealing ARB0,ARB1,ARB3 and ARB5 cycle’s composites,it is found that the thickness of intermetallic compounds at the heterogeneous interface increases with the increase of temperature.After being treated at 300 ℃,400 ℃ and500 ℃,Al4343 and Cu in the composites of ARB0,ARB1,ARB3 and ARB5 cycles undergo three processes of recovery,recrystallization and grain growth.However,the grain size of Al3003 in ARB0 and ARB1 composites changes little after being treated at 300 ℃ and 400 ℃,and abnormally large grains appear at 400 ℃.However,the abnormally large grain size of Al3003 in the ARB3 composites decreases after being treated at 400 ℃.No abnormally large grains of Al3003 in the ARB5 composite are found after treatment at 400 ℃.Tensile tests show that the strength of ARB0 and ARB1cycle’s composites decreases and the elongation increases with the increase of temperature,while the strength of ARB3 and ARB5 cycle’s composites decreases first and then increases,and the elongation increases first and then decreases.The mechanical properties of the ARB3 cycle’s composites are the best at 500 ℃,with the strength and elongation of 459 MPa and 22%,respectively.(3)After rolling ARB0,ARB1,ARB3 and ARB5 cycle’s composites,it is found that after one and two times of straight rolling,ARB0 and ARB1 cycle’s composites maintain laminar structure.The degree of necking of ARB3 composites increases,and the fracture degree of ARB5 cycle’s composites gradually increased.After two times of straight rolling,the Cu grains in the composite are distributed along the rolling direction,and the grain size decreases first and then increases.The grain size of ARB3 cycle’s composite is the smallest(0.38 μm).After one and two times of straight rolling,the mechanical properties of ARB1 cycle’s composites are the best,with the strength and elongation of 561 MPa and 4.84% and 521 MPa and 3.96%,respectively.