Effect of High Zn Content on Microstructure,Mechanical Properties and Intergranular Corrosion(IGC)Properties of Al-Mg-Si Alloys
[Purposes]Heat-treatable Al-Mg-Si alloy is widely used in transportation due to its high spe-cific strength,good formability,excellent corrosion resistance and good welding performance,which is one of the preferred materials for vehicle lightweight.However,the effect of high Zn content on the micro-structure and IGC properties of the alloys need to be further investigated.[Methods]Room temperature tensile and IGC tests,combined with SEM/EDS,EBSD and TEM characterization,were used to analyze the effect of high content of Zn on the microstructure,mechanical properties and IGC properties of Al-Mg-Si alloy.[Findings]The grain size of Zn-containing alloy was larger than that of Zn-free alloy.The room temperature tensile properties showed that the strength of the Zn-containing alloy was significantly higher than that of the Zn-free alloy,but the elongation of the Zn-containing alloy was lower.The IGC re-sults revealed that the maximum IGC depth of Zn-containing alloy was higher than that of the Zn-free al-loy.[Conclusions]The addition of Zn can reduce the amount of second phases,weaken the nailing effect on grain boundaries.and increase of the grain size of the alloy.The addition of Zn increases the number density of the fine β"phase,and promotes the precipitation of a small amount of η' phase and improve the strength of the alloy.The addition of 4 wt.%Zn promotes the transition of grain boundary precipitates from β precipitate to Zn-rich phase,reduces the grain boundary precipitates spacing,and increases the width of PFZ.As a result,the IGC resistance of the alloy is reduced.
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