In order to study the effect of Cu element on the microstructure and mechanical properties of Mg-Bi-Sn alloy,as-cast Mg-3Bi-5Sn-xCu(x=0,1,2,3,mass fraction,%)alloy was prepared.The effects of Cu element on the microstructure and mechanical properties of as-cast Mg-3Bi-5Sn(BT35)alloy were studied by OM,SEM,XRD,EPMA,Vickers hardness tester and tensile testing machine.The experimental results show that Cu element can significantly refine the grain structure of BT35 alloy.With the increase of Cu content,the grain size of Mg-3Bi-5Sn-xCu(x=0,1,2,3,mass fraction,%)alloy decreases significantly at first and then increases slightly,and the Mg-3Bi-5Sn-xCu(BTC352)alloy exhibits the smallest grain size(62.0 μm)among the four alloys.In addition,mainly Mg3Bi2 and Mg2Sn secondary phases exist in BT35 alloy,while additional Mg2Cu phase and BiSn phase appear in the alloy with the addition of Cu element.With the addition of Cu element increases from 0%to 3%,the tensile strength and elongation of the alloy increase at first and then decrease.Owing to the combined effect of grain refinement,second-phase strengthening and solution strengthening caused by 2%Cu alloying,BTC352 alloy show the best mechanical properties,its tensile strength and elongation are(249.9±6.0)MPa and(13.0±1.0)%respectively,and its fracture structure show typical transgranular fracture characteristics.
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