| Magnesium alloy and has great advantages in lightweight application of materials because of its low density and high strength,it is widely used in 3C,automobile and aerospace fields.Die casting technology is the main way to prepare magnesium alloy at present,but it is more and more difficult to meet the market demand.A new type of high performance die-casting magnesium alloy with low Si content is designed in order to obtain a higher performance and lower cost die-casting magnesium alloy.The research group found that the rapid solidified Mg-Si-Ce alloy has good mechanical properties because of the new thermal stability and high Young's modulus CeMg2Si2 rare earth phase in the alloy.The existence of rare earth phase can not only strengthen the matrix itself,but also form semi-categorization with Mg2Si phase to improve the mechanical properties of magnesium alloy.Al element is a common strengthening element,the addition of Al element can not only improve the mechanical properties of the alloy,but also improve the die-casting properties of the alloy.Therefore,the effect of the addition of Al elements on the microstructure and mechanical properties of the as-cast Mg-Si-Ce alloy is studied based on the Mg-Si-Ce alloy,and the suitable composition of the die-casting alloy is selected.The microstructure and mechanical properties of the as-cast Mg-xAl-1Si-3Ce(x=0,2,4,6)alloy were studied.It was found that the microstructure of the as-cast Mg-SiCe alloy was mainly composed of magnesium matrix,Mg2Si phase and CeMgaSi2 rare earth phase.Adding appropriate amount of Al elements not only refines the grain size of the alloy,improved the morphology and distribution of rare earth phase,but also consumed the excess rare earth elements in the alloy to form new Al-RE strengthening phase.Excessive Al elements coarsen the size of the second phase and turn the Mgi7Ali2 phase into a continuous grid,which deteriorates the mechanical properties of the alloy,so the proper amount of A1 elements is very beneficial to the properties of the alloy,among which the as-cast Mg-4Al-1Si-3Ce alloy has the best microstructure and mechanical properties.On the basis of the microstructure and mechanical properties of the as-cast alloy,the Mg-4Al-1Si-3Ce alloy with the best composition was selected as the composition of the die-casting alloy,the types of rare earth elements in the alloy were changed at the same time,and the die-casting magnesium alloy with Mg-4Al-1Si-3RE(Ce-La)was setup.The experimental results showed that the die-cast Mg-4Al-1Si-3RE(Ce,La)alloy not only precipitated micron-level strengthening phases,but also precipitated a large number of nanoscale Al-RE and REMg2Si2 rare earth phases,which can not only modify the morphology of Mg2Si phase,but also act as an effective strengthening phase itself,which can effectively strengthen the matrix of the alloy and improve the mechanical properties of the alloy.The experimental results also show that the diecasting Mg-4Al-1Si-3RE(Ce-La)alloy has excellent mechanical properties,its tensile strength,yield strength and elongation reach 263 MPa,167MPa and 12.03%,respectively,which is obviously higher than that of the typical die-casting AS41 alloy.Its excellent mechanical properties are attributed to fine grain strengthening,solid solution strengthening and second phase strengthening of dispersion.It is also found that Mg-4Al-1Si-3RE(Ce-La)has excellent friction and wear properties,and its wear mechanism is mainly oxidation wear,abrasive wear and delamination wear.The different mechanical properties and friction and wear behavior of the three die-casting alloys are caused by the addition of different rare earth elements in the alloys.Different rare earth elements will have different refinement effects on the grains and precipitate different intermetallic phase compositions,which will further lead to the difference of mechanical properties.The results show that the mechanical properties of mixed rare earth element Ce,La are better than that of rare earth element alone. |
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