JOURNAL OF RARE EARTHS, Vol. 28, No. 2, Apr. 2010, p. 316Foundation item:Project supported by the Support Plans for Science and Technology of Changchun City (2007KZ07), the Program for New Century Excellent#Talents in University, and 985 project of Jilin UniversityCorresponding author:YU Sirong (E-mail:[email protected];Tel.:+86-431-85095862)DOI:10.1016/S1002-0721(09)60104-6Microstructure and mechanical properties of friction stir welding ofAZ31B magnesium alloy added with ceriumYU Sirong (Ѣᗱ㤷)1, CHEN Xianjun (䰜ᰒ৯)1, HUANG Zhiqiu (咘ᖫ∖)1,2, LIU Yaohui (߬㗔䕝)1(1. Key Laboratory of Automobile Materials (Jilin University), Ministry of Education, and College of Materials Science and Engineering, Jilin University, Changchun130025, China; 2. College of Materials Science and Engineering, Jiamusi University, Jiamusi 154007, China)Received 19 June 2009; revised 13 December 2009Abstract:The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding (FSW). The microstructures andmechanical properties of the welded joint were investigated. The results showed that the microstructures in the weld nugget zone were uniformand with small equiaxed grains. The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the basemetal zone and the weld nugget zone. The ultimate tensile strength of AZ31B magnesium alloy added with 0.5 wt.% Ce was 270.41r4.48 MPa,and its elongation to fracture was (17.71r0.60)%. The ultimate tensile strength of FSW joint was 237.97r2.53 MPa, and its elongation to fracturewas 6.63r0.60%. The fracture locations of FSW joint were in the heat-affected zone. The ductile fracture was the main fracture mode. The ulti-mate tensile strength of the sample along the direction of the weld was 270.02r1.45 MPa, and its elongation to fracture was (17.08r0.39)%. Themicrohardness in the weld nugget zone was slightly lower than that in the base metal. The microhardness in the thermo-mechanical affected zoneand heat affected zone was lower than that in the weld nugget zone. The microhardness increased from the surface to the bottom of the weld.Keywords:AZ31B magnesium alloy; friction stir welding; microstructure; mechanical property; rare earthsMagnesium and magnesium alloys are the lightest struc-tural materials in industrial applications[1]. They have lowdensity, high specific strength, high specific stiffness andexcellent machinability[2]. Therefore, magnesium alloys arewidely used in the aerospace, automotive, and electronicsindustry fields[3,4]. In order to reduce the weight for the pur-pose of energy saving, one of the important measures is toreplace steel and iron parts with magnesium alloy parts[5].Most of magnesium alloy parts were mainly produced usingthe casting process now[6]. After hot deformation treatment,the microstructures were refined and the casting defects wereeliminated to produce magnesium alloys with higherstrength and better ductility[7]. Therefore, the wrought mag-nesium alloys are expected to be new types of high-per-formance structural materials in this century. As one of thewrought magnesium alloys used widely, AZ31B magnesiumalloy has good ductility, but poor strengths at room tem-perature and high temperature[8]. Thus rare earth, such as CeDQG#La, is used to refine the grains of AZ31B wroughtmagnesium alloy and enhance its mechanical properties[9,10].
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