Effect Of Al And Ca Microalloying On Microstruc Ture And Mechanical Properties Of Mg-10Gd Alloy

Mg-Gd rare earth magnesium alloys are widely used in aerospace,automotive,military and other fields due to their excellent heat and corrosion resistance and creep resistance.However,excessive Gd content will increase the cost of the alloys and is not good for the lightweight of the alloys.Therefore,researchers add other alloying elements to Mg-Gd alloys to replace part of Gd elements.It is hoped to develop rare earth magnesium alloys with low cost and high performance.In this paper,the changes of microstructure of Mg-10Gd alloy after solution treatment and addition of Al and Ca elements were studied by optical microscopy（OM）,scanning electron microscopy（SEM）and X-ray diffraction analysis（XRD）.The effect of Al/Ca content on grain refinement of Mg-10Gd alloy and the evolution law of the second phase in the matrix were systematically studied.The microstructure changes of Mg-10Gd-xAl-yCa alloy during solution treatment were analyzed.The Vickers hardness and tensile test at room temperature were carried out,and the effects of Al and Ca contents and solution treatment on the mechanical properties of Mg-10Gd alloy were analyzed.The hot compression behavior of as-cast Mg-10Gd-xAl-yCa alloy was studied,and the hot compression constitutive equation and hot working diagram of Mg10Gd-1.5Al-0.5Ca alloy were established.The results are as follows:（1）The addition of Al and Ca elements to Mg-10Gd alloy can effectively refine the alloy grains.With the increase of Al/Ca,Al2Gd phase can be used as effective nucleating particles,and the alloy microstructure changes from coarse cylindrical dendrite to fine equiaaxial crystal,among which Mg-10Gd-1.5Al-0.5Ca alloy has the smallest grain.is 43.18μm.（2）Mg-10Gd-xAl-yCa alloy is mainly composed of α-Mg,Al2Gd,（Mg,Al）3Gd,Mg5Gd and Mg2Ca phases when Al and Ca elements are added.When the content of Ca is 0.5%,all Ca elements are dissolved into the matrix.When the content of Ca is more than 0.5%,ternary eutectic reaction occurs in Mg-10Gd alloy and coarse eutectic phase（α-Mg+MgsGd+Mg2Ca）is formed along the grain boundary.With the decrease of Al/Ca,petal-like（Mg,Al）3Gd eventually changed into short rod-like and granular.When 1.5%Al and 0.5%Ca elements are added to Mg-10Gd,the alloy has the best comprehensive mechanical properties.The tensile strength of the alloy is 210.7MPa,and the elongation reaches 15.6%,which is 71.3%and 200.5%higher than that of Mg-10Gd alloy,respectively.（3）After the addition of Al and Ca elements,Mg-10Gd-lAl-1Ca alloy can effectively nail grain boundaries,hinder the diffusion of elements,and inhibit the grain growth of Mg-Gd-Ca alloy and the Oswald curing of the second phase due to the good thermal stability of the high melting point Al2Gd phase in the solution treatment.（4）At the strain rate of 0.1s^-1,the flow stress and peak stress of Mg-10Gd-xAl-yCa alloy decrease with the increase of temperature.With the decrease of Al/Ca,the alloy is more prone to crack during the process of hot compression.According to the hot working diagram of Mg-10Gd1.5Al-0.5Ca alloy under different strains,the workable zone temperature of the alloy is 675K～711K,and the strain rate is 0.047～1s^-1.