镁合金钨极氩弧焊接头深冷强化机制

Mechanism of deep cryogenic strengthening of magnesium alloy joint welded by TIG

关键词:  镁合金  TIG焊  焊接接头  深冷处理  强化机制

Key words:  deep cryogenic treatment  AZ31 magnesium alloy  welding joint  strengthening mechanism

摘要:

针对镁合金焊接接头软化问题,文中提出了AZ31镁合金TIG焊接接头深冷强化方法,进行了镁合金TIG焊接工艺试验和焊接接头的-160℃,8 h深冷处理试验;深冷处理使镁合金焊接接头抗拉强度从212.4 MPa提高到246.6 MPa;用X射线衍射仪(XRD)和透射电子显微镜(TEM)等观测了焊接接头深冷前后的微观组织与结构,分析了焊接接头深冷强化机理.结果表明,深冷处理使镁合金TIG焊接接头形成亚晶结构,第二相Mg17Al12颗粒弥散析出,提高了基体连续性,第二相颗粒数量增加,使接头组织细化并获强化,深冷处理使焊接接头的晶粒发生转动与位错转化为位错环,使接头组织产生孪晶,强化了焊接接头.

Abstract:

One of the welding problems for magnesium alloy is the softening of the welded joints. Deep cryogenic treatment is put forward to strengthen joints of AZ31 magnesium alloy welded by TIG. The welding experiment and deep cryogenic treatment test for 8h at -160℃ are carried out. The tensile strength of the joints treated by deep cryogenic is tested as well. The microstructure of the deep cryogenic joints of magnesium alloy has been examined with the optical microscope,the scan electron microscope,the transmission electron microscope and the X-ray diffraction. The mechanism of deep cryogenic strengthening joint of AZ31 Magnesium alloy has been analyzed. The results show that tensile strength are increased from 212.4 MPa to 246.6 MPa and the strength coefficient is increased from 83.7% to 97.1% by deep cryogenic treatment. Moreover,the subgrain structure is formed in the welded joints of AZ31B by deep cryogenic treatment. The Mg17Al12 particles precipitate and improve the continuity of base material. The number of second phase particles increases,which refines the microstructure of welded joints by TIG of AZ31B magnesium alloy and strengthen mechanism. The dislocation of deep cryogenic joints changes into the dislocation loop and twin crystal is formed as well. The orientation of grain crystal of welded joints of AZ31B has change,resulting in the grain rotation after deep cryogenic treatment.