Corrosion Behavior Of New Ignition-proof Magnesium Alloy

Magnesium alloys have been widely used in the automotive industry,electrocommunication,aerospace,national defense/military and other industrial filelds due to their low density,high specific strength,environmental friendly,and abundant in resources.However,Mg alloys are chemically active,which result in poor chemical stability.In addition,corrosion resistance of magnesium alloys also not good and retard their application so far.In order to solve the issues as mentioned above,i.e.inflamable and bad corrosion resistance,Ca and Y?0.3 wt.%Ca;0.2 wt.%Y?were added in AZ91D alloy to investigate their effects on microstructure,mechanical properties,and corrosion resistance.The XRD,OM,SEM,EDS,Vickers microhardness test,Universal mechanical properties test,Weight loss of immersion and Salt spry test etc.were used for microstructure characterization,mechanical properties and corrosion resistance tests.In addition,various heat treatment and caliber rolling were carried out to study the influence on corrosion resistance of AZ91D alloys with and without Ca and Y addition.The results showed that the melt stability has been greatly improved in Ca and Y bearing alloy,because the melt surface can produce a dense and thick oxide film between the melt and atomosphere effectively.Addition of Ca and Y can promote grain nucleation,thus the grains are obviously refined as well as the number of?-Mg₁₇Al₁₂2 has been decreased,and morphology of?-Mg₁₇Al₁₂2 also changed from continuous network to granular dispersion.The Ca are proned to exist in?phase by solid solution,which make the?phase more stable,and the Y element tend to generate thermal stable Al₈Mn₄Y precipitated in AZ91D alloy.Heat treatment suggested that with the addition of Ca and Y,the solution temperature of the alloys were improved and the peak aging time was prolonged.Moreover,after rolled deformation,the grains are finer and twinning occurs in the alloy because of dynamic recrystallization.Due to grain refinement strengthening and plastic deformation strengthening,these wrought alloys exhibit best mechanical properties at high temperature and low rolling speed.Furthermore,corrosion test results showed that the corrosion resistance of the alloys can significantly increase with Y addition,but degraded by Ca remarkably,because the galvanic corrosion was accelerated by more Ca addition.Among all state of alloys,the as-cast alloys represented best corrosion resistance,while solution heat treatment alloy given worst corrosion behavior.After heat treatment,the decreased?phase in the alloy can not act as a corrosion barrier,which in turn,the degrade corrosion resistance was observed.Especially,the caliber rolling seems not good for corrosion resistance,because of the corrosion sensitivity of the alloy was improved by introducing a large number of dislocation,twinning and other defects,and the alloy deformed at high temperature and low rolling speed exhibited very bad corrosion resisitance.