【作者】 孙昊；

【导师】 刘黎明；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2008， 硕士

【摘要】 在金属结构材料中镁合金的密度是最低的。与其他金属材料及工程塑料相比，镁合金具有很高的比强度和比刚度，优良的阻尼减震性能、电磁屏蔽性、机械加工性能和铸造性能，这些优点使镁合金的产品在航空、汽车、电子等领域获得了越来越广泛的应用。随着越来越多镁合金焊接件在工业上的应用，研究和推广镁合金高效、优质焊接工艺已成为实际生产的迫切要求。前期对镁合金活性电弧焊研究，发现活性剂能够大幅度提高电弧焊熔深能力。本文着重探索活性剂对镁合金激光焊的影响。发现在AZ31B镁合金低功率激光焊接的过程中加入活性剂，大幅度提高了镁合金低功率激光焊的熔深。通过系统的工艺试验分析了各工艺参数对焊接过程的影响规律，并总结出活性剂作用效果明显的规范区间。分析微观组织和接头性能并与传统激光焊对比发现：接头组织均为典型的激光焊组织，熔合线清晰，热影响区窄；晶粒大小不规则但与单独激光焊相比尺寸有所增加，焊缝中出现了一定量的氧化物夹杂，导致焊接接头拉伸强度有所降低，接头的断裂形式由韧性断裂转变为韧脆混合断裂。活性剂增加激光焊熔深的主要原因为：活性剂的使用提高了激光作用初期试样对激光能量的吸收率。本文为改善镁合金A-TIG焊接头性能，在氧化物活性剂中添加一定量的增强相颗粒。发现A-TIG焊的熔深比未涂敷活性剂有了明显增加，使熔深增大了1.5倍以上。且SiC在活性剂中的比例对熔深影响不大。分析焊缝微观组织发现添加在活性剂中的微小SiC陶瓷颗粒较均匀分布在焊缝中。焊缝力学性能测试结果表明：TiO₂活性剂中加入SiC陶瓷颗粒后焊缝的拉伸强度有所增加，当SiC在活性剂中的质量分数为40％时，焊接接头的拉伸强度达到母材强度的89.6％，与传统TIG焊接头的强度相当。焊缝强度提高的主要原因为：氧化物活性剂改变了传统TIG焊熔池的流动方式，使加入的SiC颗粒随着熔池液态金属的流动顺利进入熔池，并且由于熔池的强烈搅拌作用而均匀分布于焊缝内部，对焊缝金属起到弥散强化的作用。更多还原

【Abstract】 As the lightest structure material, Magnesium alloys have many advantages, such as low density, high specific strength, damping capacity, better mechanical properties, recyclable and so on, which are attracting more attention from the domestic and foreign. With the wide use of magnesium alloy structure in manufacture, it is requested to investigate and apply the high-efficiency and quality welding technique of magnesium alloy. A-TIG welding of magnesium was studied previously, and results showed that applying the activating flux on the AZ31B alloy surface leads to an increase in weld penetration depth.The behaviors of laser welding wrought magnesium AZ31B alloy with activating fluxes were studied in the paper. The results showed the fluxes can increase the weld penetration of the laser welding. The effect of parameters on penetrations was studied by systemic experiments. The microstructures and mechanical properties were analyzed and compared between the welds with and without flux. The microstructures were all of typical laser welding, and the fusion line was clear, the heat affect zone was narrow. An irregular and larger grain size was exhibited in the weld metal prepared with flux than that without flux. Oxide particles were found in the weld metal when flux was used. The results of tensile tests showed that weld metal with flux was lower than that without any flux. The main mechanism for the increases of penetration was that the flux coat absorbed more laser energy during the early period of laser action.A-TIG welding of magnesium alloy was investigated, and oxide powder mixed with enforced particles was selected as the flux. The results indicated that the penetrations with different percentage of SiC in the flux were almost the same, and that they were 1.5 times than that without flux. It was showed that the SiC particles were distributed dispersed in the weld bead. The mechanical properties of the weld beads were obviously improved by tensile tests, when SiC was added in the flux TiO₂. When flux 60%TiO₂+40%SiC was used, the tensile strength of the weld bead reached 89.6% of base metal, and it was almost the same with that of the weld bead without any flux. The reason of hardening of the weld bead with SiC in the weld metal was as followed: the oxide flux changed the traditional pool flow, and the SiC particles were involved in the pool and distributed uniform in the weld metal owning to intense stir of pool. The weld metal was hardened by dispersion hardening of the SiC particles.更多还原