Investigation On Fabrication And Properties Of Mg-Sn-Zn-Al Alloys

The alloying composition of Mg-6Sn-3Al-1Zn was found by orthogonal experiment.The effect of alloying elements on the microstructures and properties of Mg-6Sn-3Al-1Zn alloy was studied throughby change the adding amount of alloying elements in Mg-6Sn-3Al-1Zn alloy.The Mg-Sn-Al-Zn alloy was prepared by vacuum induction melting method under CO₂+SF₆ atmosphere.The microstructures were characterized by metallographic microscope,X-ray diffraction,scanning electron microscopy and tensile testing machine.The effect of Sn?Zn and Al elements and their additions on the microstructure,mechanical properties and tensile fracture mechanism of alloys were investigated.It is found that there are two kinds of phases,the ?-Mg and Mg₂Sn in the Mg-xSn-3Al-1Zn?x=3,4.5,6,7.5?alloys.The quality of Mg₂Sn content in the alloy increases with the addition of Sn content.When the Sn content exceeds 6wt%,the morphology of Mg₂Sn changes from granular to skeletal,and most of the phase is distributed in the grain boundaries.It is found that the alloying element distributionof Zn is more homogeneous in the alloy,and the Sn and Al elements are enriched at the grain boundary.The few of the ?-Al₂Mg₅Zn₂ phase is observed in the Mg-7.5Sn-3Al-1Zn alloy,and as the base of the Mg₂Sn phase.The room temperature tensile fracture of the Mg-xSn-3Al-1Zn?x=3,4.5,6,7.5?alloysexist tearing edge,when Sn content alloyat 6wt% and 7.5wt%presence of dimples,and 6wt%Sn content of the alloy dimples ismore deep.It is a typical ductile fracture mechanism.As-cast Mg-6Sn-3Al-xZn?x=1,2.5,4,5.5?alloys exist phases ofa-Mg and Mg₂Sn.When the Zn content is increased to 2.5wt%,the ?-Mg₃₂?Al,Zn?₄₉ phase appears in the alloy,and itsnumber increase as the Zn content addition.The Al and Sn elements are enriched at the grain boundary,and the Zn content gradually increases to make Znelement enrichment more obvious at the grain boundary.The enrichment of Zn and Al elements at the grain boundary is caused the?-Mg₃₂?Al,Zn?₄₉phase formation and size expansion.In addition,the Zn element increases the yield strength of the alloy,buttensile strength and elongation is weakened.With the increase of Zncontent,the Mg-6Sn-3Al-xZn?x=1,2.5,4,5.5?alloy appear cracks in the fracture,and showing the existence of local intergranular fracture characteristics,when the Zn content of 1wt%,the fracture has a clear tear edge and some local small dimple appearance.At this time,the fracture is dominated by ductile fracture.As-cast Mg-6Sn-1Zn-xAl?x=1,2,3,4?alloys precipitates a-Mg and Mg₂Sn phases.With the increase of the Al element content,the amount of Mg₂Sn precipitates gradually increases and the size grow up.When the Al content is more than 3wt%,the morphology of Mg₂Sn in the alloy is changed from granular to skeletal,increased in number and mainly distributed in the grain boundary.With the increase of the content of Al,and the enrichment in the grain boundary is more and more heterogeneous.There is a tearing edge in the alloy at room temperature,and there is a dimple in the fracture of the alloy when the Al content is 3wt%,which is the embodiment of the ductile fracture.The distribution of the second phase in the as-extruted Mg-Sn-Al-Zn alloy is more uniform.With increase of the alloying element content,particles size of the phase increases gradually.Tensile strength of as-extruded Mg-6Sn-4Zn-3Al alloy is324.2MPa at room temperature,the yield strength is 125.1MPa,and the elongation is20.7%.It has best mechanical propertiesin the as-extruted Mg-Sn-Al-Zn alloys.In Mg-xSn-3Al-1Zn?x=3,4.5,6,7.5?alloys,which appears the maximum ductile fracture morphology in theSn addition3wt%alloy,and it is the typical ductile fracture morphology.With the increase of Zn content in theMg-6Sn-3Al-xZn?x=1,2.5,4,5.5?alloys,the crack and dimple in the extrusion fracture increases obviously.In the Mg-6Sn-1Zn-xAl?x=1,2,3,4?alloys,the fine tearing edges are distributed at the fracture,which is the embodiment of ductile fracture mechanism.