The Study About Microstructure And Creep Ability Of Mg-5Al-xSn-5Ca

Magnesium alloy has many advantages such as low density, excellent damping, high strength, good casting performance, and good machining properties. Therefore it is significant practice practical significance to research such alloy. In this paper, we first study the microstructure of the Mg-5Al-x Sn-5Ca alloy, the thermal stability of Mg-5Al-2Sn-5Ca. Based on which alloy creep performance, microstructure of Mg-5Al-1.5Sn-5Ca, under the isothermal treatment and as-cast state alloy were investigated, the results are summarized as follows:(1)The connected hard skeleton structure mainly composed of Mg2(Al,Ca), Ca Mg Sn and Al2 Ca, the thick Ca Mg Sn phase can be observed when the content of Sn is 1.0%. With the content of Sn increases, the hardness of the alloy is improved.(2)Under the condition of isothermal treatment, the microstructure evolution for Mg-5Al-2Sn-5Ca and Mg-5Al-1.5Sn-5Ca is similar, the hard skeleton structure has a good thermal stability. There was no obvious change for the connected hard skeleton structure when it was isothermal treated at temperature below 350℃, while chained structure was obtained when it was isothermal treated at 450 for 48 h.Furthermore, there was no obvious ℃distortion for the quenching sample after it was exposed at 600 for 24 h.℃(3)At the room condition, the tensile strength of the Mg-5Al-1.5Sn-5Ca alloy is 145.2MPa, the ductility is 5.2%. When the tensile temperature is 175℃, the ultimate of the Mg-5Al-1.5Sn-5Ca alloy is 117.3MPa, the ductility is 5.8%. The temperature is at 200℃, the tensile strength of the Mg-5Al-1.5Sn-5Ca alloy is 93.7MPa, the ductility is 5.9%.(4)Under the condition of creep temperature of 200 and loading stresses of 50, 60 and ℃75 MPa, respectively, the creep life, and the steady creep rate for as-cast ATX525 alloy is 191, 97 and 9hrs, and 3.5×10-8, 3.9×10-7and 2×10-6s-1, respectively. Under the condition of creep temperature of 175 and loading stresses of 75, 85, and 90 MPa, respectively, the creep life,℃ and the steady creep rate for as-cast Mg-5Al-1.5Sn-5Ca alloy is 109, 81 and 62hrs, and 1.25×10-7, 1.67×10-7 and 1.25×10-6s-1,respectively.(5)Heat treatment(450℃/48h) and ageing(200℃/72h) were employed for as-cast Mg-5Al-1.5Sn-5Ca alloy. Under the condition of creep temperature of 200 ℃and loading stresses of 50, 60 and 75 MPa, respectively, the creep life, and the steady creep rate for as-treated Mg-5Al-1.5Sn-5Ca alloy is 270, 110 and 45 hrs, and 1.67×10-8, 1.11×10-7 and 2×10-7s-1,respectively.(6)The creep mechanism of Mg-5Al-1.5Sn-5Ca alloy is grain boundary sliding controlled by the hard skeleton structure.