Effects Of Sn Addition On Microstructure, Mechanical Properties And Corrosion Resistance Of High-alloyed Mg–Al–Zn Alloys

Magnesium alloys has been considered as the most promising light weight structural materials with high specific strength,good thermal and electrical conductivity.However,commercial wrought Mg alloys are normally with low alloying contents to ensure formability,hence the strength is often difficult to meet the demand because of the lack of enough second phases to strengthen the alloys.Besides,poor corrosion resistance of magnesium alloys is another main factor which limits its development.To obtain excellent performances and broaden applications of wrought Mg alloys,it is greatly necessary to develop new Mg alloys with high alloying contents and study the corrosion resistance of these alloys.Our work aim at opening a door for the development of high-content wrought Mg alloys with tailored properties.In the present work,high-alloyed Mg–6Al–4Zn–xSn?x=1,2 and 3 wt.%?alloys were performed by conventional extrusion and rolling,the effects of Sn addition on the microstructure,mechanical properties and corrosion resistance were studied.The main conclusions can be summarized as follows:?1?By conventional extrusion,it was found that average grain size of these alloys decreases significantly from¹1 to⁴?m as Sn contents increasing from 0 to 3 t.%.The amounts of Mg₂Sn and Mg₁₇Al₁₂2 particles with more Sn addition are ontinuously increased.More importantly,the deformation along c-axis of AZ64 lloy at room temperature is dominated byextension twins while the ominate deformation mechanism in AZT643 alloy is pyramidal<+>slip.?2?The strength and elongation both increase gradually with additional Sn omplement.Hereinto,as-extruded Mg–6Al–4Zn–3Sn alloy exhibits optimal echanical properties with a simultaneous high strength and ductility at room emperature,i.e.yield strength of²07 MPa,ultimate tensile strength of³66 Pa and elongation of¹9%.The high yield strength should be mainly attributed o improved grain refinement strengthening and precipitation strengthening when n content reaches to 3 wt.%,while the advantageous combination of ultimate ensile strength and ductility results from strong strain hardening ability and the nduced activity of non-basal<+>slip.?3?As-extruded AZ64-xSn alloys were processed by hard-plate rolling after heat reatment process.It was found that AZT642 alloy exhibits the best combination f strength and ductility,i.e.ultimate tensile strength of³80 MPa and elongation f¹8%.However,with increasing Sn contents,the strength and ductility of the lloys decrease again.The decreased strength could be attributted to the coarse rain size,resulting in the weak refinement strengthening effect.Besides,the oarse particles?¹0?m?act as initiation sites for fracture,which have adverse ffect on the overall mechanical properties of alloys.?4?Compared with AZ64 alloy,the corrosion resistance of AZ64 alloy can be mproved by increasing Sn contents.It was indicated that the alloy exhibits the est corrosion resistance with the lowest corrosion rate when Sn content reaches o 2 wt.%.The improved corrosion resistance is because of the gain boundaries arrier effect and the enhanced electric potential of matrix by Sn solid solution.?5?The corrosion resistance of investigated alloys decreased when Sn contents more han 3 wt.%.This is mainly because a large number of grain boundaries could act s cathode which form the corrosion grooves between with magnesium matrix.In addition,the increased Mg₂Sn and Mg₁₇Al₁₂2 particles could provide more driving force for the galvanic corrosion.