The Study On Growth Morphologies Of Primary Mg₂Si With Zr And Sb Modification In Al-Mg-Si Alloy

As a kind of effective strengthening phase in Al–Mg–Si alloys, the shape, size anddistribution of the primary Mg2Si play a key role in alloy mechanical properties. Themodification treatment in the alloys cause more and more attention by people, due to thismethod is not only easy operation, low cost but also effectively optimize the morphologiesof Mg2Si. However, in spite the modification primary Mg2Si of Al alloys in a variety ofmodification mechanisms and processes have more in–depth researches in previous studies,but those theories are still not comprehensive, and the study on the modification mechanimand process with Zr and Sb co-modification in primary Mg2Si of Al–Mg–Si alloy is less. Inaddition, the research of modification treatment effects on mechanical properties ofAl–Mg–Si alloy is also not much, therefore, having an in–depth study on zirconium,antimony modified in the Al–Mg–Si alloy is necessary. This study can provide a reference onmaking better development of Mg2Si strengthen of lightweight aluminum alloy in thefurture.In this study, we study the growth morphologies and modification mechanisms ofprimary Mg2Si with Zr and Sb co-modification in Al–Mg–Si alloy and this modificationtreatment effects on mechanical properties of Al–Mg–Si alloy, and some results are given asfollows:(1) Zr–Sb co-modification treatment had a good effect on the primary and eutecticMg2Si in Al–20Mg2Si alloy. In0.2wt.%of Zr modification condition, the primary Mg2Si ofAl–20Mg2Si alloy showed the thick dendrites and its sizes were about100μm; meanwhile,adding0.2wt.%of Sb in Al–20Mg2Si alloy, the primary Mg2Si of alloy showed the thindendrites and its sizes falled in between40μm and50μm; The primary Mg2Si presentedcomplete octahedron with0.2wt.%(Zr–Sb) co-modification in Al–20Mg2Si alloy,and itssizes were about30μm, so Zr–Sb modification effect was obviously better than the single effect. When Zr: Sb was1:2, the modification effect was better than the other ratio effect,and the content of Zr–Sb was0.5wt.%, it had best effects on primary and eutectic Mg2Si inAl–20Mg2Si alloy, in this case, primary Mg2Si presented truncated octahedron and themorphologies of eutectic Mg2Si were short rod and spot shape.(2) The primary Mg2Si presented complete octahedron with0.2wt.%(Zr–Sb)co-modification in Al–20Mg2Si alloy.Octahedral primary Mg2Si growth process was: crystalnucleusâ†'<100> crystal direction growthâ†'<110> crystal direction growthâ†'octahedraledge growthâ†'octahedral skeletonâ†'complete octahedron. The modification mechanism ofprimary Mg2Si with Zr and Sb co-modification in Al–Mg–Si alloy was: on one hand, thecombintion of Al and Sb generated AlSb that is a high melting point compound，and AlSb asheterogeneous core to refine primary Mg2Si; on the other hand, Zr retrained primary Mg2Sigrowth by adsorption poison.(3) Zr and Sb co-modification had a great influence on the room temperature, hightemperature tensile properties of Al–20Mg2Si alloy in extrusion condition. At roomtemperature, the tensile property of alloy without modification was153MPa, however, aftermodification became188MPa, increased by23%; Under the condition of100oC, the tensileproperties of alloy with modification and without modification were136MPa and154MParespectively. Under the condition of150oC, the tensile property of alloy withoutmodification was120MPa, and the tensile property of alloy increased to142MPa bymodification, in addition, the tensile property of alloy decreased with tensile temperatureincreasing. Zr and Sb modification had a certain influence on various mechanical propertiesof Al–20Mg2Si alloys in cast condition, such as compression, hardness and wear etc.