在2.5 mm厚6061铝合金光纤激光穿透焊接实验的基础上，着重研究了焊接热输入对焊缝成形的影响。结果表明，光纤激光穿透焊的焊缝熔宽随焊接热输入的增加而增加，且背面熔宽的增幅更快。激光功率越高，获得稳定全熔透焊缝的热输入调节范围越大。焊接接头熔合区附近为柱状晶组织，焊缝中心为柱状晶和等轴晶的混合组织。随焊接热输入的逐渐降低，焊缝区显微组织逐渐细化，且混合组织中等轴晶所占比例逐渐减少。另外，随热输入的逐渐降低，焊缝区的平均显微硬度缓慢增长，焊缝区上部和下部的显微硬度数据分散性逐渐减小，当焊接热输入约为90 J/mm时，焊缝上部和下部的显微硬度对称性最好。

Based on the experiments of fiber laser beam welding 6061 aluminum alloy with 2.5 mm thickness, the effects of heat input on full penetration weld appearance are investigated. The results show that the weld width of the penetration weld increases with increasing the heat input, and the change amplitude of the weld back is greater than that of the weld front. When the stable fully penetration weld is used, a higher laser power results in a broader adjustable range of the heat input. Fine columnar microstructure is formed near the fusion zone, and the mixed microstructures (including columnar grains and equiaxed grains) is distributed in the center of the weld. When the heat input is reduced, the microstructures of the weld zone tend to fine, and the proportion of the equiaxed grains in the mixed microstructures decreases. In addition, with the heat input decreasing, the microhardness of the weld zone increases slightly, and the microhardness data dispersity between the weld up and weld bottom decreases. When the heat input is about 90 J/mm, the microhardness symmetry of weld up and weld bottom is best.