Study Of Preparation,Microstructure And Mechanical Properties Of High Magnesium Al-Mg Alloy Sheet

Because of its excellent corrosion resirtance,Al-Mg alloy is a preferred choice for offshore industrial platform.However,the strength of Al-Mg alloy can not meet the higher command of mechanical properties in offshore industrial platform.Then,the reseearch of developing high magnesium Al-Mg alloy was conducted to achieve higher strength.However it was found that the alloy was more and more difficult to cast and hard to be deformed when magnesium content is higher than 7wt.%.In order to solve this problem,high magnesium Al-Mg alloy was selected as research base,and the composition design of the alloy,the casting method and metalforming,microstructure and mechanical properties were studied.The main contents are as follows:Firstly,the centrifugal melt filling behavior was studied by water model simulation with Fluent software.Bubbles was produced by the disturbance of the newly poured melt.The bubbles would mainly segregated near the centrifugal rotation axis under centrifugal field,and gradually disappear with the increase of radial distance and depth.Centrifugal casting experiments were studied to determine the suitable parameters for this study.Adopted centrifugal rotation speed was 850r/min,pouring temperature as 720℃,and melt weight was about 7Kg.Equiaxed grains existed in centrifugal ingot,and the average grain size was about 25μm.Secondly,samples 400℃/24 h solution treated of Al-10 Mg alloy were uniaxial compressed under series deformation temperatures and strain rates.Deformed microstructure was characterized by EBSD,and flow stress behavior,necklace structure formation and expansion during dynamic recrystallization were studied.In view of the problem that high magnesium aluminum alloy was sensitive to hardening rate during thermal mechanical processing,the process of high temperature aging treatment applied before hot deformation was proposed.Double passes compression was applied to aging treated samples,and flow stress behavior and hardening rate behavior were analyzed.The effects of β phase on accelerating dynamic recrystallization nucleation and obstructing texture formation were studied by EBSD,XRD and EPMA.Thirdly,high magnesium and microalloying aluminum cold rolled sheet was obtained by “hot rolling in warm temperature-intermediate heat treatment-cold rolling” process.Engineering stress-strain curves and macrofractography morphology of sheet were analyzed.The tensile strength,yield strength and elongation of Al-xMg binary sheet along the rolling direction was improved simultaneously with the increase of magnesium content.With the increase of magnesium content,the anisotropy of tensile strength increase d,but the anisotropy of elongation gradually decreased,with no obvious variation of yield strength.The elastic modulus of the sheet can be improved by addition of Zr and Ti.However Mn had no effect on elastic modulus.Microalloying method would improve the strength at the expense of decreasing of elongation.