低Cu高强Al-Zn-Mg-Cu合金搅拌摩擦焊接组织与性能

Microstructure and Properties of Low Cu and High Strength Al-Zn-Mg-Cu Alloy Friction Stir Welded Joints

分别采用300、900r/min对低Cu高强Al-Zn-Mg-Cu合金板材进行搅拌摩擦焊接,研究合金焊接接头的显微组织和力学性能。结果表明,焊接过程中微米级AlMnCr相变化不明显,晶内纳米级和晶界亚微米级MgZn2相发生回溶与粗化。随着焊接转速增加,析出相回溶程度加剧,焊接接头晶粒尺寸增大。在晶粒和析出相共同作用下,合金焊接接头硬度呈“U”型分布,前进侧热影响区硬度略低于后退侧,焊核及热机影响区硬度较低,是焊接接头断裂位置,受“S”线缺陷影响形成锯齿形断口形貌。综合分析,低Cu高强Al-Zn-Mg-Cu合金在300r/min下接头性能较好,抗拉强度、屈服强度、伸长率和焊接系数分别为393MPa、261MPa、12%和80%。

Friction stir welding of low Cu and high strength Al-Zn-Mg-Cu alloy plate was carried out at 300r/min and 900r/min.The microstructure and mechanical properties of the welded joints were analyzed by means of metallographic microscope,scanning electron microscope,transmission electron microscope,Vickers hardness and tensile test.The results show that there is absence of obvious change of micrometer AlMnCr phase during the welding process,and the dissolution and coarsening occur in intracrystalline nanoscale MgZn2phase and grain boundary submicron MgZn2phase.With the increase of welding speed,the degree of precipitate dissolution is increased,and the grain size of welded joint tends to be increased.Under the combined action of grains and precipitates,the hardness of the welded joints of the alloy is characterized by approximate U-shaped distribution.The hardness of the heat affected zone on the advancing side is slightly lower than that on the retreating side,and that of the welding nugget and heat affected zone is relatively low,which is the fracture position of the welded joints,presenting zigzag fracture shape affected by the"S"line defect.The welded joints of low Cu and high strength Al-Zn-Mg-Cu alloy have the better properties under the low rotational speed of 300r/min.The maximum tensile strength,yield strength,elongation and welding coefficient reach 393MPa,261MPa,12%and 80%,respectively.