厚高强铝合金VPPA-MIG复合焊接热过程的计算与分析

Thermal process calculation and analysis analysis in VPPA-MIG hybrid welding of thick high-strength aluminum alloy plates

摘要:

为了进一步提高变极性等离子弧(VPPA)-金属惰性气体(MIG)复合焊接的数值计算精度，采用高速摄像机对VPPA-MIG焊接的热源特性进行了分析，开发并优化了一种变极性热组合源模型对VPPA-MIG焊接热过程进行了数值分析。该模型考虑了VPPA加热形式的周期性变化。此外，为了更准确地表达复合焊接，同时考虑了正、反极性两阶段复合热源的耦合作用。通过试验获得焊缝尺寸和热循环验证了数值计算结果。模拟结果表明，VPPA-MIG复合焊的熔宽小于MIG焊的熔宽，复合焊接具有较强的穿透能力。VPPA-MIG焊接与MIG焊接在热输入形式和热过程上存在明显差异，直接影响了焊接接头的组织与力学性能。通过对比VPPA-MIG焊与传统MIG焊的微观组织发现，VPPA-MIG复合焊接过程中复合电弧的摆动有利于接头中产生细小均匀的晶粒。从二者焊接接头的显微硬度和抗拉强度可以看出，VPPA-MIG复合焊接接头具有较小的软化倾向。

Abstract:

To further improve the numerical calculation of variable-polarity plasma arc (VPPA)–metal inert gas (MIG) welding, the heating behavior of VPPA-MIG welding was analyzed using a high-speed camera. A variable-polarity finite element model was developed and optimized for the numerical analysis of the thermal process in VPPA–MIG welding. This model incorporated the heating mode of the VPPA with its periodic variations. Moreover, in order to more accurately express the hybrid welding conditions, the coupling interaction between the two heat sources in the electrode-negative and electrode-positive phases was taken into account. Experiments were conducted to obtain weld dimensions to verify the predicted results. This simulation results showed that the fusion width of the VPPA–MIG welded joint was smaller than that of the MIG welded joint, and the penetration ability of hybrid welding was also stronger. There was a conspicuous difference in the form of heat input and thermal process between VPPA-MIG and MIG welding, which directly affected the microstructure and mechanical properties of the welds. Comparing the microstructures of the VPPA-MIG and the traditional MIG welds, it was found that the swing of the hybrid arc in VPPA-MIG welding can facilitate the production of fine aluminum grains in thick aluminum alloy plates. Consequently, the hardness and tensile properties of the hybrid welded joints were significantly higher than those produced under MIG traditional welding.