Effect Of Ca And CaO On The Structure And Properties Of ME21 Alloy

This paper uses two different ways to add Ca in the alloy ME21,and a series of studies for the alloy,and to explore the effects of extrusion on microstructure and mechanical properties of the alloy microstructure,compared to two different for the manner of adding Ca alloy caused by different effects,and design experiments compared oxidation resistance and flame resistance of the alloy.It concluded that the results are as follows:(1)The structure of the as-cast ME21,ME21+Ca and ME21+Ca O alloys is mainly coarse grain structure,with a very small amount of alloy phases and some particles distributed along the grain boundaries.There are also many particles in the matrix,such as Mn elemental particles and Mg₁₂Ce It is the main second phase in the alloy.The addition of Ca element reduces the grain size of ME21 alloy.After solution treatment+hot extrusion process,the coarse grains in ME21,ME21+Ca and ME21+Ca O alloys are transformed into fine and uniform equiaxed crystals.(2)The DSC results show that the as-cast ME21,ME21+Ca and ME21+Ca O alloys mainly contain the matrix?-Mg and the second phase Mg₁₂Ce,Mn elementary particles.Adding Ca O to the ME21 alloy will generate a high melting point phase with a melting point of about 633?,it may be Mg₂Ca.(3)The tensile strength and yield strength of the as-cast ME21+Ca alloy are higher than those of the as-cast ME21 alloy,but the elongation is slightly inferior;compared with the as-cast ME21 alloy,the as-cast ME21+Ca O alloy has little difference in tensile strength.The yield strength is increased,and the alloy elongation is significantly reduced.(4)After hot extrusion,the tensile strength,compressive strength and elongation of the three alloys have been greatly improved.The tensile strengths of the extruded ME21,ME21+Ca and ME21+Ca O alloys were 322.5MPa,262.3MPa and 248.2MPa,respectively,the tensile yield strengths were 262.4MPa,234.9MPa and 199.2MPa,and the elongation reached 9.4%,respectively.16.1%and 18.1%.Among them,ME21+Ca alloy has the best overall performance.(5)The ignition temperature of the as-cast ME21,ME21+Ca and ME21+Ca O alloys are 822?,849?and 870?respectively.The addition of Ca can improve the flame resistance of ME21 alloy,which may be related to the alloy oxide film after adding Ca.The structural change is related,that is,the flame resistance:ME21+Ca O>ME21+Ca>ME21.The ignition temperatures of the extruded ME21,ME21+Ca and ME21+Ca O alloys are 803?,819?and 826?,respectively.(6)According to the results of the oxidation resistance test performance and the oxidation kinetic curve,the surface burr coverage of the alloy after being kept at 470?for 12 hours is ME21>ME21+Ca?ME21+Ca O,and the weight gain of the sample after the TGA test is ME21>ME21+Ca O>ME21+Ca.Based on the above experimental results,it can be considered that the antioxidant performance:ME21+Ca>ME21+Ca O>ME21.(7)After XRD and SEM line scanning are used to analyze the oxide film of the as-cast ME21,ME21+Ca and ME21+Ca O alloy,it is determined that the main components of the oxide film of the ME21 alloy are Mg O and Ce₂O₃,and the Mg O is located on the outer layer of the oxide film and inside the oxide film.The layer is a composite layer of Mg O and Ce₂O₃;the oxide film of ME21+Ca and ME21+Ca O is mainly composed of Mg O,Ce₂O₃ and Ca O,and the alloy oxide film of ME21+Ca and ME21+Ca O is divided into 3 layers,namely the outermost layer.Mg O,the Ca O and Mg O composite layer of the secondary outer layer,and Ce₂O₃ of the inner layer.