Research On The Structure And Properties Of CaO Modified AZ31 Magnesium Alloy

Magnesium alloy is the lightest structural metal.There are many advantages such as low density,high stiffness,high damping coefficient,recoverable and others.It was widely used in many industries as a lightweight material and environmentally friendly materials.But,due to hexagonal close-packed structure,magnesium alloy is difficult to be deformed,which its applied rang is restricted on large scale.Grain refinement is considered to be an effective way to improve alloy performance.In this paper,the grain size of AZ31 alloy was improved by alloying and plastic processing to improve the forming ability and mechanical properties of the alloy.AZ31 alloy is widely used in the field of production.CaO powder was added during AZ31 alloy molten.The effects of processing parameters and CaO content on the microstructure and properties of the alloy were studied by extrusion and friction stir processing.After experimental data analysis,some results can be drawn as follows.1.CaO reacts with AZ31 alloy melt and Al2 Ca phase forms,grain size had refined in the process of alloy melting and plastic deformation.2.The mechanical properties of the alloy increase with the increasing of the CaO content.When the addition of CaO reaches 1wt.%,the yield strength and tensile strength increase to 28.6% and 17.3% respectively compared with that of the AZ31 alloy.The strength of the alloy decreases with the increase of the extrusion temperature.Increasing the extrusion ratio can improve the dynamic recrystallization of the alloy and grain size is refined,which mechanical properties of alloy are improved.The results show that the best process parameters are extrusion temperature of 300℃and extrusion ratio of 9.3.With the increase of CaO content,the texture intensity decreases.The texture intensity of AZ31 alloy is 17,and the texture intensity decreased by 52.9% adding CaO content.So,mechanical properties of alloy are improved.4.Friction stir processing machining can obtain uniform equiaxed crystal structure.The mechanical properties and plasticity are improved by friction stir processing.When the stirring speed is 1200r/ min and the content of CaO is 1wt.%,the mechanical properties reach the best one.The tensile strength increased by 3.5%,elongation increased by 15%.5.The addition of CaO reduces the corrosion resistance of the alloy.In the electrochemical corrosion test,the corrosion potential is reduced by 35 m V.During the immersion process,the weight loss rate of the alloy increases with the increase of CaO addition.