Effects Of Cold Rolling Reduction And Annealing Process On Microstructure And Properties Of Ultra-Thin Cu/Al Composite Sheets

Ultra-thin Cu/Al composite sheets are widely used in armored cables,COB packaging,air-cooled fins and many other small and micro fields,so higher requirements are put forward for the thickness,shape and bonding effect of Cu/Al composite sheets.In this thesis,0.06～0.09 mm ultra-thin Cu/Al composite sheets were prepared by using a four roll micro rolling machine designed by the laboratory.The effect of cold rolling reduction and annealing process on the microstructure and properties of ultra-thin Cu/Al composite sheet was studied by means of optical microscope（OM）,scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,X-ray diffraction（XRD）,room temperature uniaxial tensile test,peel strength test and microhardness test.The main contents and research results of this thesis are as follows:（1）The cold rolling experiment was carried out by using a four high micro mill designed by the laboratory.With a rolling reduction of 55%～70%,a rolling speed of7.07 mm/s and a surface roughness of 240#abrasive paper after grinding,0.06～0.09mm ultra-thin Cu/Al composite sheets with good shape could be prepared.（2）The ultra-thin Cu/Al composite sheet was heat treated by four annealing temperatures of 350℃,400℃,450℃and 500℃,and three holding time annealing processes of 1 h,2 h and 3 h.The results showed that with the increase of annealing temperature and holding time,the microhardness difference between the composite interface of ultra-thin Cu/Al composite sheet and the metal matrix on both sides became larger and larger,and the peel strength first increased and then decreased with the increase of annealing temperature,When the rolling reduction is 60%,and the annealing temperature is 400℃,the holding time is 1h,the peel strength of the extremely thin Cu/Al composite sheet reaches the maximum,and the composite effect reaches the best state.（3）The room temperature uniaxial tensile test was carried out on the ultra-thin Cu/Al composite sheet after four annealing temperatures and three holding time were used.The results showed that the grain size of copper and aluminum increased significantly due to annealing,and the tensile strength and elongation of ultra-thin Cu/Al composite sheet decreased due to the increase of the grain size of copper and aluminum.The comprehensive mechanical properties of the ultra-thin Cu/Al composite sheet are better than those of the two metal matrixes.（4）After annealing,the morphology of the diffusion layer at the composite interface of the extremely thin Cu/Al composite sheet was observed.It was found that the thickness of the interface diffusion layer gradually increased with the increase of annealing temperature and holding time.When the annealing temperature was 400℃,there was a small hole defect in the interface diffusion layer.When the annealing temperature reached 450℃,there were some very obvious microcracks in the diffusion layer.With a thickness of more than 10μm the diffusion layer greatly reduces the peel strength of the composite sheet.（5）The point composition and X-ray diffraction of the diffusion layer at the interface of the extremely thin Cu/Al composite sheet were comprehensively analyzed.The results showed that the composition of the diffusion layer compounds increased from two kinds of Al₂Cu and Al₄Cu₉to three kinds of Al₂Cu,Al₄Cu₉and Al Cu with the increase of the annealing temperature.The annealing temperature had more influence on the content of the diffusion layer compounds than the holding time.（6）The observation of element diffusion at the interface of ultra-thin Cu/Al composite sheet shows that the increase of annealing temperature and holding time will cause a large number of copper and aluminum atoms to migrate at the interface,and increase the range of mutual diffusion of copper and aluminum elements at the interface,thus improving the element diffusion at the composite interface.（7）The area of intermetallic compound distributed on the Al side peel surface of the ultra-thin Cu/Al composite sheet after peeling gradually increases with the increase of annealing temperature and holding time.When the holding time is 3 h,large microcracks appear on the intermetallic compound.At the annealing temperature of 400～500℃,Al₂Cu,Al Cu Al₄Cu₉and Al₂Cu₃are metallurgical bonding layers composed of hard brittle phase intermetallic compounds.The formation of a large number of hard brittle phase compounds greatly reduces the tensile strength and peel strength of ultra-thin Cu/Al composite sheets.