镁合金与不锈钢的瞬间液相扩散连接

Transient Liquid Phase Bonding of Magnesium Alloy AZ31B and 304 Stainless Steel

以Cu箔为中间夹层对AZ31B镁合金与304不锈钢进行瞬间液相扩散连接,研究了焊接接头的微观结构和连接强度。结果表明,在510℃/30 min、530℃/10 min下进行扩散连接时,接头界面区没有出现共晶液相,界面结合较弱;520℃/30 min、530℃/20 min时,接头界面区形成Mg-Cu共晶液相,焊缝宽度显著增加,界面结合强度提高;530℃/30min时,镁基体一侧形成350μm的层状扩散区,接头显微组织依次是Mg-Cu共晶组织层、富Mg固溶体层、弥散分布于镁合金基体的Mg17(Cu,Al)12相和分布于镁合金晶界的Mg-Cu-Al三元化合物所组成的镁合金基体渗透区,其剪切强度达到最大(52 MPa);540℃/30 min、530℃/40 min时,界面扩散区的共晶液相发生等温凝固,镁合金基体晶界处Mg-Cu-Al三元金属间化合物呈连续网状分布,接头的剪切强度降低。AZ31B基体发生了再结晶及晶粒长大。

Transient liquid-phase bonding of magnesium alloy（AZ31B） to stainless steel（304） was performed using a copper interlayer. The microstructure and bonding strength of the bonded joint were studied. The results show that when the welding condition is 510 ℃/30 min or 530 ℃/10 min, no eutectic phase is observed in the welded joint and the metallurgical bond is weak. When the welding condition is 520 ℃/30 min or 530 ℃/20 min, the joint interface forms Mg-Cu eutectic. The weld width increases significantly and interfacial bonding strength improves. At 530 ℃/30 min, a laminar diffusion region with a width of about 350 μm forms at the magnesium side in the welded joint. Microstructures are Mg-Cu eutectic layer, followed by Mg-rich solid solution layer, Mg17（Cu,Al）12 dispersed in magnesium alloy matrix and permeability zones of Mg-Cu-Al ternary compounds distributed in grain boundaries of magnesium alloy. The shear strength of the joint reaches the highest value of 52 MPa. Under the welding condition of 540 ℃/30 min or 530 ℃/40 min, isothermal solidification occurs in eutectic liquid on the interfacial diffusion zone and the joint shear strength decreases, which is attributed to continuous network distribution of Mg-Cu-Al compound along the magnesium grain boundary. Recrystallization happens and grains grow in the AZ31 B matrix.