Studies On Interface?Microstructure And Mechanical Properties Of Al/Mg/Al Laminated Composites Processed By Accumulative Roll-bonding(ARB)

Magnesium and its alloys are the lightest metal structure materials,however,their plasticity at room temperature are low and corrosion resistance are poor,which restrict their application widely.Aluminum and its alloys have good plasticity,toughness,and excellent corrosion resistance.Through combining Al and Mg via ARB process,on the one hand it can greatly improve the corrosion resistance of Mg plate through the outer layer of Al coating,on the other hand the grain size of the matrix can be refined by rolling process,which can improve the mechanical properties of the composite sheet.A wide range of applications of Al/Mg/Al multi-layer composite sheets can be expected in the fields of instrument,electrical appliances,automobiles,3C products,aerospace,etc.In this dissertation,Al/Mg/Al multi-layer composite sheets were prepared by means of accumulative roll-bonding(ARB).Optical microscopy,scanning electron microscopy,energy dispersive spectroscopy,electron backscatter diffraction and transmission electron microscopy were used to study its interface,microstructure and fracture morphologies with different cycles of rolled and annealed Al/Mg/Al multi-layer composite sheets.Hardness test and uniaxial tensile test were used to study the mechanical properties with different cycles of rolled and annealed Al/Mg/Al multi-layer composite sheets.And the second pass was analyzed in detail as its good overall performance.The Al/Mg/Al multi-layer composite sheets were successfully fabricated under the condition of preheating at 400 ?.The best plasticity of rolled samples occurred at the first pass was 18%,and the highest strength occurred at the third pass was 240MPa.The overall performance was improved after annealing at 250 ?.The multi-layer composite sheets achieved metallurgical bonding between Al and Mg layers,As the cycle increased,the bonding quality improved,the intermetallic compounds of Al3Mg2 and All2Mg17 were formed in the same time,which reached to 23?m,brought defects into the interfaces of Al/Mg/Al.The grain size got to elongate,refine and homogenize in different layers,the first layer has smaller grain size than center part.Finally,the grain size of the magnesium layer was refined from?15?m to?2.5?m,the aluminum layer was also refined from?150?m to?2?m.After the third pass,the strength reached 240MPa and the plasticity dropped to 2.3%.The overall performance of Al/Mg/Al multi-layer composite sheets improved after annealing.Especially,the second pass was heated at 250 ? for 10min,60 min and 120 min,respectively,it was found that the average thickness of the intermetallic compounds increased from 13.1?m,13.8?m to 15?m.During the annealing process,discontinuous recrystallization occurred in Al and Mg layers.With the increase of the annealing holding time,the hardness of composite sheets decreased first and then increased again.After annealing for 60min,the average elongation increased from 2.27%to 11.78%,which was 4 times higher than that of the rolled samples.While the tensile strength decreased by only 23MPa,The fracture mode of Al/Mg/Al multi-layer composite sheets changed from brittle fracture into ductile fracture.