低温下钎焊铝合金能够避免母材受热发生软化.研究了使用纯Sn超声钎焊纯Al时,初晶 α(Al)对Al/Sn界面显微组织和结合强度的影响.结果表明,在液态Sn中,α(Al)的{111}面的表面能和生长速度最小,因此,析出的初晶 α(Al)的形态为{111}面包围的正八面体.超声能够起到提高形核率并细化初晶 α(Al)颗粒的作用.在较长的超声和保温时间下,Al/Sn界面会析出大量八面体初晶 α(Al)颗粒,使界面呈现出一种起伏不平的形貌,增加了界面实际结合面积和咬合作用.超声作用40 s,保温10 min时界面的结合强度达到63 MPa.
Soldering aluminum alloys at low temperature have great potential to avoid softening of base metals. Pure Al was soldered with pure tin assisted by ultrasound. The influence of primary α(Al) on the microstructure of Al/Sn interface and its bonding strength was studied. It is found that the primary α(Al) in liquid tin tends to be octahedron enclosed by Al {111} facet with the lowest surface free energy and growth rate. The ultrasonic action could increase the nucleation rate and refine the particles of primary α(Al). For the longer ultrasonic and holding time, a large amount of the octahedral primary α(Al) particles crystallize at the Al/Sn interface. The bonding interface exhibits the profile of rough dentation, resulting in an increment of bonding interface area and the effect of mechanical occlusion. The bonding strength at interface could reach 63 MPa with ultrasonic time of 40 s and holding time of 10 min.
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