用Nd:YAG固体脉冲激光焊接器对厚度为0.65 mm的DP500双相钢进行了激光焊接试验，对脉冲激光焊缝表面和横截面形貌进行了分析，重点研究了不同脉冲激光频率下焊缝凝固特征及晶粒组织与硬度的关系。试验结果表明，在形成焊缝的每个焊斑可分为重叠区和未重叠区，并且随着脉冲激光频率不同，不但形成的焊缝形态和焊斑重叠率不同，而且还存在晶粒组织的差异。同时，硬度出现波动性，最低硬度值出现在焊斑重叠区，最高硬度值出现在焊斑未重叠区。随着脉冲激光频率的提高和焊斑重叠率的增大，晶粒组织的差别不但逐渐减小，而且沿焊缝正剖面中心线的硬度波动性也逐渐降低。

The welding test of DP500 dual-phase steel sheet of 0.65 mm is implemented by the Nd:YAG solid pulsed laser welder. The pulsed laser weld surface and cross-section morphology are analyzed, and the paper focuses on the weld solidification characteristics under different pulse laser frequencies and the relationship between microstructure grain and microhardness. The result shows that each of the welding spots forming the weld seam can be divided into two parts: welding spot overlap region and unoverlap region. With the change of the pulse laser frequency, the morphology of weld and the welding spot overlapping ratio both change, and the microstructure grain exhibits heterogeneity. Meanwhile, microhardness distribution appears to be fluctuant, the minimum microhardness value appears in the welding spot overlap region while, the maximum microhardness value appears in the unoverlap region. With the pulse laser frequency increasing, the difference of microstructure grain decreases and the fluctuation of the microhardness distribution along the longitudinal section of the weld center is also gradually reduced.