Microstructure And Mechanical Properties Of Casting WE43-Zn Magnesium Alloy

Commercial WE43 magnesium alloy is one of the most successful heat-resistant alloy with high mechanical properties under booth room temperature and elevated temperature and is widely used in aeronautic and aerospace engineering.However,it is found that,when producing a new type of helicopter casing,WE43 alloy shows poor mechanical properties which is far from the requirement during the low solidification cooling rate brought by sand casting.Hence,it is critical to find solutions to enhance the mechanical properties of WE43 alloy.Alloying with Zn is an effect method to adjust the microstructure and mechanical properties of magnesium alloy.There are many reports concerning the enhanced mechanical properties of Mg-RE alloy through Zn alloying.However,there lacks the report on the WE43 alloyed with Zn.It is necessary to study the effect of Zn addition on the microstructure and mechanical properties of WE43 alloy and adjust the heat treatment process parameters accordingly.Based on WE43 alloy,different contents of Zn were added to the alloy prepared by metallic mold casting and sand mold casting.Systemic study on the effect of Zn content on the microstructure and mechanical properties of WE43 alloy was carried out and Zn content was optimized according to the results.After that,we produced a casting helicopter casing using the optimized WE43-Zn alloy.Influence of heat treatment on the microstructure and mechanical properties of the WE43-Zn alloy casting was also studied.Heat treatment process parameters were optimized to provide reference for engineering practice.The results indicate that LPSO structure forms in the inner grains of the as-cast Zn-containing alloy.Area fractions of the LPSO structure and eutectic are increased with the increase of Zn content.The relatively low solidification cooling rate brought by sand mold casting favors the formation of LPSO structure.After solution treatment,those alloys containing 0.5wt.%Zn or less become single-phase solid solution while the1.0wt.%Zn containing alloy has additional residual eutectic and shows 15²0?m smaller in average grain size.Tensile strength of the as-quenched alloy raises with increasing Zn content.After aging treatment,with increasing Zn content,ultimate tensile strength increases firstly and decreases then.WE43-1.0Zn alloy shows weak precipitation hardening behavior because of the residual eutectics.WE43-0.5Zn alloy performances the highest strength due to the strong precipitation hardening and solid solution strengthening.As a result,the WE43-1.0Zn alloy shows the highest elongation due to the poor precipitation hardening and fine grains.Low content of Zn promotes strength while high content of Zn decreases strength through reducing the solution limit of RE.The peak-aged WE43-0.5Zn alloy perform the highest overall tensile properties.After that,we produced a helicopter casing using WE43-0.5Zn alloy.Optimization on the heat treatment was carried out.Results showed that strength of the WE43-0.5Zn alloy casting decreases with increasing aging temperature.Precipitates are mainly fine dense??and??phases when peak-aged at 200? and 225? while coarse sparse coupled?₁/??phases in the 250?×10h over-aged condition.200? and 225? aged alloy shows high strength with ultimate tensile strength more than 320MPa.The 250? aged alloy shows poor strength but high elongation.Take both strength and ductility into consideration,the WE43-0.5Zn alloy casting helicopter casing shows the highest overall mechanical properties with YS=198MPa,UTS=277MPa,EL=7.5%when aged at 250? for 10h after solution treated at 525? for6h.Hot water?about 90??quenching is adopted after solution in case of crack.Under such heat treatment condition,the helicopter casing meets the requirements of application.