Study On The Phase Equilibria In The Mg-rich Corner Of The Mg-Sn-Ca System And Mechanical Properties Of As-extruded Mg-Sn-Ca Alloys

Mg-Sn-Ca ternary alloy system is a non rare-earth alloy system.The precipitation of the system has strong precipitation strengthening effect because of the addition of Sn,Ca element.However the research on the phase equilibria in Mg-rich corner is still lack of accurate experimental data.In this work,Mg-rich Mg-Sn-Ca alloys are investigated by many different techniques to study the phase equilibria in the Mg-rich corner.Based on this,three kinds of Mg-Sn-Ca alloys with same Mg but different Sn and Ca contents were selected to study the mechanical behavior of the as-extruded Mg-Sn-Ca alloys.The results are as follows:(1)For the as-cast Mg-Sn-Ca alloys,in order to get CaxMg2-xSn only on the a-Mg matrix,the Ca/Sn ratio should be set between 0.62～0.99.At a higher Ca/Sn ratio,Mg2Ca phase precipitates,and at a lower Ca/Sn ratio,Mg2Sn precipitates.(2)The isothermal section of the Mg-rich Mg-Sn-Ca system at 500 ℃ has been established.At 500 ℃ in the Mg-rich region of the Mg-Sn-Ca ternary system,there are three binary phase equilibria,which are:(Mg)+CaxMg2-xSn,(Mg)+Mg2Sn and(Mg)+Mg2Ca,and two ternary phase equilibria,which are:(Mg)+Mg2Ca+CaxMg2-xSn and(Mg)+Mg2Sn+CaxMg2-xSn.(3)There are two four-phase eutectic reactions in the Mg-rich corner,which are L?(Mg)+Mg2Ca+ CaxMg2-xSn at 518 ℃ and L?(Mg)+Mg2Sn+ Ca,Mg2-xSn at the temperature of 561 ℃.(4)The addition of Ca element leads to the precipitation of Mg2Ca phase,which brings about the increase of the strength to 353.82MPa.The plasticity slightly decreases.The more Sn element,the more Mg2Sn phase precipitates,the strength is about 284.48MPaand the plasticity is about 10%.