Preparation Of Al/Mg/Al Laminated Composite Frabricated By Hot Rolled And Investigation Of Microstructure And Mechanical Properties

The poor corrosion resistance and low room-temperature formability of Mg alloys limit its widespread application. The Al(5052) alloy sheets which is of excellent corrosion resistance and nice plastic was cladded to the surface of Mg(AZ31B) alloy plate. In this research, Al(5052)/Mg(AZ31B)/Al(5052) laminated composite was fabricated by three different hot rolling processes. The effects of hot rolling processes and annealing processes on the microstructure of substrate, interfacial microstructure, interfacial bond strength and integrated mechanical properties were explored. Inverse analysis of elastic constant and mechanical properties of IMCL(interfacial metallic compounds layer) of interface caused by annealed was performed.For the laminated composite plates, keeping structural integrity is crucial. But the interfacial stress would delaminate the interface because the difference of mechanicas of cladding and substrate when the laminated composite plates subjected to the external load. The conventional testing methods can not get the normal bond strength and the shear bond stress due to the tiny size in thickness of laminated composites which is of higher bonded interface. Therefore, two novel testing methods were proposed to solve the difficulty. The normal bonded strength was tested by Four-point bending method with an adhesive butt-joint, the result showed that the measured range increased from 20 MPa to 40 MPa by the proposed method. An unconstrained cladding-uniaxial tensile(UCC-UT) specimen was used to get the interfacial shearing bond strength. Theoretical analysis and formula were developed for these two methods.When hot rolling was performed upon the recrystallization temperature to frabricate Al(5052)/Mg(AZ31B)/Al(5052) laminated composite, the evolution of microstructure is extremely complicated caused by the plastic deformation mechanism, in order to elucidate the microstructural evolution of substrate, the theoretical model is presented to describe the temperature distribution and flowing deformation in different thickness of the cladding and substrate based on the microstructural characteristic of substrate. In this model, the substrate was divided into three zones along the thickness direction: interfacial zone(Region I), near-interfacial zone(Region II) and core zone(Region III). The evolutionary process of substrate of Al/Mg/Al laminated composite fabricated by three different hot rolling processes can be clarified with this model.For the Al(5052)/Mg(AZ31B)/Al(5052) laminated composite fabricated by three different hot rolling methods, the research showed that:(1) When changing the reduction, the different deforming behavior of 5052 and AZ31 B would develop higher shearing stress, which refine the coarse grain, and the width of Region I increased with increased reduction; for Region II, the twin grains, coarse grains transformed to shear band and DRX grains, the refined DRX grains would replace all the coarse grains; for Region III, the deformed degree is lower than that of Region II, there is a lot of twin grains, coarse grains and the DRX grains on the bound of coarse; the interfacial bond strength increased with the reduction; the tensile experiment suggested that the elongation is 12.3% when reduction is 30%; the ultimate tensile strength is 304.4 MPa when reduction is 70%.(2) When changing rolling speed, the grains refined obviously in Region I, and the width of Region I increased firstly and then decreased with increased the rolling speed, for Region II, the twin grains substantial increased, the coarse grains reduced, and then the DRX grains increased; for Region III, the DRX grains is growing gradually, the twin grains is reduced gradually, and the flow line is increasingly apparent; the interfacial bond strength increased first and then decreased; the intergrity mechanical properties is excellent when rolling speed is 15 rpm, the yield strength(YS) is 216.2 MPa, the ultimate tensile strength(UTS) is 274.8 MPa, the elongation(EL) is 14.1%.(3) when changing rolling temperature, the grains refined is not obviously in Region I when rolling temperature is from 200℃ to 300℃, when rolling temperature exceeded 300℃, the grains refined and the width of Region I increased; for Region II, the twin grains decreased and the coarse grains increased; for Region III, the twin grains decreased less than that of Region II; the interfacial bond strength increased gradually with increased rolling temperature; the YS is 238 MPa, the UTS is 278.2 MPa, the EL is 9.49%.The above research showed that the mechanical properties are changed with the hot rolling process, but not obviously. This is particularly relevant with the complicated microstructures and strainharding of Al(5052)/Mg(AZ31B)/Al(5052). In order to improve microstructure of substrate and mechanical properties of laminated composites, the Al(5052)/Mg(AZ31B)/Al(5052) fabricated by hot rolling process(400℃+15rpm+40%). And then the annealed processes were performed on the prepared specimens. In order to investigate the effect of annealed processes on evolution of substrate, interfacial microstructure, interfacial bond strength, topography of delaminated surface and uniaxial tensile behavior, different annealed systems were performed. The experimental data showed that relief temperature is 150℃. The integrated mechanical properties are excellence when annealed at 150℃+1h. The temperature of no reaction diffusion at interface is 200℃. The research showed that the interfacial bond strength decreased with the increased annealed time. The superior laminated composite can be gained when annealed time is 1h~2h. When annealed temperature is 300℃, annealed time is 30 min, the thin IMC layer about 1.6μm would formed at interface. The IMC is hard and brittle phase, in spite of which, the thin IMC layer can improved the interfacial bond strength and the integrated mechanical properties of laminated composite due to the size effects.The fractured processes of IMCL contained two phases were investigated by experiment. Based on the experimental phenomenon, the fractured processes were divided into three regions: perfect region, defective region and failure status. The research showed that the transverse cracks in defective region can conjoin cladding and substrate, so the Al/Mg/Al laminated composite can go on working. The mechanical properties of IMCL was analyzed by inversed method combined VRH method and Rule of mixture in elastic stage. The elastic modulus is 49.8GPa, the possion ratio is 0.301, the ultimate tensile strength(UTS) is 131.81 MPa, the fractured strain is 0.2702% and the fractured plastic strain is 0.026%.