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以2.2 m/min激光扫描速度,采用对接和搭接两种方式高速焊接0.7 mm薄板殷瓦合金。借助金相显微镜和扫描电子显微镜观察焊缝显微组织,讨论焊缝中心的热裂纹形成机理,对比分析不同接头形式的热裂纹敏感性。实验结果显示,殷瓦合金的高速激光焊缝为铸态单相奥氏体树枝晶。对接焊缝中心出现热裂纹,而搭接焊缝未发现热裂纹。分析认为,在树枝晶凝固最后阶段,焊缝两侧树枝晶粒的大角度晶界能γgb大于2倍液态薄膜固/液界面能sγl,液态薄膜完全桥接需要临界过冷度ΔTb。殷瓦合金散热系数低,过冷度不足,焊接残余拉伸应力rδ将导致液态薄膜开裂。对接时容易出现热裂纹。而搭接时开裂的液态薄膜有上层液态金属流入补充,能有效降低焊缝的热裂纹敏感性。
At a speed of 2.2 m / min laser scanning speed, 0.7 mm thick thin-plate Invax was welded by both butt and lap. The microstructure of the weld was observed by means of metallographic microscope and scanning electron microscope. The formation mechanism of the thermal crack in the center of the weld was discussed. The thermal crack sensitivity of different joints was analyzed. The experimental results show that the high-speed laser weld of Inwa alloy is as-cast single-phase austenite dendrite. Hot cracks appear in the center of the butt weld and hot cracks are not found in the lap weld. The analysis shows that the large-angle grain boundary energy γgb of the dendrite grains on both sides of the weld is greater than 2 times the solid-liquid interface energy γγ in the final stage of dendrite solidification, and the critical undercooling ΔTb is required for complete bridging of the liquid film. Yinwa alloy low coefficient of heat dissipation, undercooling insufficient welding residual tensile stress rδ will lead to liquid film cracking. Hot cracks easily occur during docking. The lap splitting of the liquid film has the upper liquid metal influx added, can effectively reduce the weld thermal cracking sensitivity.