An Al-Zn-Mg-Mn-Zr alloy containing 0.26wt% Sc was melted,and then hot rolling,cold rolling, solid solution and aging heat treatment were carried out on the as-cast alloy in turn;Next,the alloy was welded by argon arc welding method using an welding wire with similar composition.The microstructure,tensile properties and hardness of welded joint were studied,and the existence form and acting mechanism of the trace amounts of Sc in the welded joint were discussed.The results show that weld zone contained typical as-cast dendrite microstructure.The heat affected zone was be divided into half fusion zone and softening zone.The half fusion zone was near weld zone and the zone contained a thin layer of equiaxed crystal microstructure;The softening zone was near the base metal and the zone was fiber microstructure and coarsening grains due to obvious recrystallization.The tensile strength,yield strength and elongation of the welded joint was about 481 MPa,320 MPa,9.97%, respectively,the welding coefficient of the weld joint achieved 0.826-8.28.Primary Al3 (Sc,Zr)particles formed in the welded joint due to the trace amounts of Sc and Zr,the Al3 (Sc,Zr)could act as the core of heterogeneous nucleation,consequently significantly refined as-cast grains in the molten pool.The variation tendency of hardness of the welded joint firstly increased,then decreased and then increased from the center of weld zone to base metal on both sides.%首先熔炼了含钪(质量分数为0．26％)的Al-Zn-Mg-Mn-Zr合金,铸态合金依次经热轧、冷轧、固溶、时效热处理后,采用成分相近的焊丝对其进行氩弧焊,研究了焊接接头的组织、拉伸性能和硬度,并讨论了钪在焊接接头中的存在形式及作用机理.结果表明：焊缝区为典型的铸态树枝晶组织,热影响区又可分为半熔合区和软化区,半熔合区靠近焊缝,区内出现了一层较薄的细小等轴晶组织；软化区靠近母材,发生了明显的再结晶现象,其组织特征为加工纤维组织和粗化的再结晶组织；焊接接头的抗拉强度、屈服强度、伸长率分别约为481 MPa,320 MPa,9．97％,焊接系数为0．826~0．828；微量钪、锆元素在接头中形成的初生Al3(Sc,Zr)粒子可作为非均匀形核的核心,显著细化熔池区域的铸态晶粒；接头硬度从焊缝中心向两侧母材呈先增大后减小然后再增大的趋势.
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