Research On Bulging Behavior Of5052/AZ31/5052Aluminum-coated Magnesium Composite Sheet

Aluminum-coated magnesium composite sheet is a new-fashioned material with bothadvantages of aluminum and magnesium. The lightweight, corrosion-resistant and aseismicmaterial can be used to produce machinery, coachwork, aerospace equipment, etc. It canguide industrial development trend and has broad application prospects. In order to make thesheet widely used in industry, sophisticated research theories including basic mechanicalproperty, micro-properties, formability, etc. should be improved. This topic studied the effectof bulging process on bonding properties of5052/AZ31/5052aluminum-coated magnesiumcomposite sheet at macroscopic experiment, micro-analysis and numerical simulationrespectively.Basic mechanical properties of the aluminum-coated magnesium composite sheet arestudied by uniaxial thermal tensile experiment at170℃,200℃and230℃. Tensile strength,yield strength and strain hardening index decreased with the increasing of the temperature,however, elongation and average coefficient of normal anisotropy increased. Averagecoefficient of normal anisotropy reached maximum0.87and mean difference value of normalanisotropy coefficient reached minimum0.11at230℃.Anisotropy of the sheet isinsignificant at230℃.Through the determination of thinning rates of bulging specimens and analysis of thedistribution law at170℃and230℃, it is found that the bulging specimen deformed underequi-biaxal strain at230℃has the maximum thinning rate48.8%, curves of thinning rate inthree directions are close to each other, the thickness of each direction is approximately same.Observed fracture and bonding interface of the aluminum-coated magnesium compositesheet by SEM (equipped with EDS), it was showed that, brittle rupture occurred at170℃while ductile rupture occurred at230℃. Bulging process eliminated defects in interface structure and increased mechanical occlusion area, it had little influence on relative thicknessof diffusion layer, so it was helpful to improve interface bonding strength. Mg and Al waswell distributed under equi-biaxal strain at230℃, diffusion depth of Mg reached themaximum48.57μm while diffusion depth ofAl had no obvious change.Simulated bulging process at170℃and230℃by DYNAFORM and contrasteddifferences between simulation results and practical results, it is found that, simulation valuesof limit bulging height and thinning rate were less than experimental data, but the differencewas no more than10%, the variations of limit bulging height under different strain state gotby simulation were same with actual situation.Based on the research above, results are summarized as follows: The aluminum-coatedmagnesium composite sheet had better plastic forming properties at230℃.Bulging processnot only affects little on thickness diffusion layer but promote elements on both sides ofbonding interface distributing uniformly to improve interface bonding strength. Simulate theprocess of stamping by finite element software before actual production have advantages tooptimizing process parameters and product structure to guide production effectively andimprove efficiency and yield successfully.