烧结NdFeB永磁体激光点焊的显微组织特征

Characteristics of microstructures in laser spot welds of a sintered NdFeB permanent magnet for different welding modes

为了研究烧结NdFeB永磁体在激光焊接条件下的冶金行为,利用2kW连续光纤激光器对N48H永磁体进行了激光点焊,分析了"深熔"和"热导"两种激光焊接模式下焊点的显微组织特征,并对显微组织的形成机理进行了初步分析。结果表明:两种焊接模式下热影响区(HAZ)中均存在液化裂纹,熔合区均由Nd2Fe14B相和α-Fe相组成,熔核内部均为亚μm的Nd2Fe14B超细等轴晶。深熔焊熔核上表面有密集生长的α-Fe柱状枝晶,而热导焊没有;深熔焊时富Nd相在熔核上表面外围富集,热导焊时富Nd相在熔核上表面中心富集。不同焊接模式下,不同的温度场及熔池流动行为是形成接头区不同显微组织的根本原因。

The metallurgical behavior of laser welds in NdFeB permanent magnets is investigated using laser spot welds made with N48H with the deep penetration mode weld or the heat conduction mode weld using a 2 kW continuous fiber laser. The joint microstruetures show that the heat affected zones （HAZ） of both joints have cracks caused by melting of the grain boundary phase, with the fusion zones having Nd2Fe14B and α-Fe, while the nuggets in both joints have ultrafine equiaxed grains of Nd2Fe14B. a Fe columnar dendrites develop on the surfaces of the nuggets in the deep penetration mode weld but not in the heat conduction mode weld. A Nd-rich phase is found on the edge of the nugget surface for the deep penetration spot weld and in the middle of the nugget surface for the heat conduction spot weld. Different temperature fields and flow patterns are believed to be the main causes of the different microstructures for the different welding modes.