粉煤灰/二氧化硅活性剂在Q235钢A-TIG焊中的应用

Application of fly ash/silica active flux on A-TIG welding of Q235 steel

为了探究粉煤灰作为A-TIG焊活性剂的可行性,以粉煤灰和不同含量的二氧化硅制备复合活性剂在Q235钢基体表面进行A-TIG焊,研究了复合活性剂成分含量对焊缝截面形貌、显微组织和元素分布的影响.结果表明:采用粉煤灰-40%SiO_2作为复合活性剂进行A-TIG焊时,可将6 mm厚Q235钢板一次性焊透,焊缝深宽比可达到0.85;焊缝出现明显的中间收缩倾向,呈"深口杯"状,可实现单道焊双面成型的效果;其焊缝柱状晶数目较多、组织排列规则且具有方向性,熔合区和热影响区组织均匀细小,可降低焊接母材的过热倾向;相对于100%SiO_2活性剂,Si元素的溶入量和溶入深度显著增加,这说明粉煤灰中其他成分的存在对Si元素溶入焊缝、进而增加焊缝熔深起到促进作用.采用粉煤灰-40%SiO_2为活性剂进行A-TIG焊时焊缝熔深的增加机理可能是以电弧收缩理论为主,但考虑到Al元素溶入较深且溶入量较多,粉煤灰中其他物相又十分复杂,在高温电弧作用下各物相之间相互反应放热致使电弧热输入增加、其他组分在熔池中改变了熔池表面张力温度梯度等均可能致使焊缝熔深增加.

In order to analyse the feasibility of fly ash as active flux in A-TIG welding, fly ash and SiO2 with varying contents were used as composite active fluxes to weld the substrate of Q235 steel, and the effects of active fluxes on weld penetration, microstructure and element distribution were studied. Experimental results show that Q235 steel plate with thickness of 6 mm could be fully welded with fly ash and 40%SiO2 as composite active fluxes, and the depth-to-width ratio of weld reaches up to 0.85. The middle of the weld shaped with deep glass presents remarkable shrinkage tendency, which could realize the effect of one-side welding with back formation. The columnar crystals show a preferred orientation, while the microstructure in fusion zone and heat affected zone exhibit a fine and uniform distribution which could reduce the overheat in the welding. Compared with 100% SiO2 as active fluxes, the dissolved quantity and depth of element Si increasing markedly indicates that other components in fly ash could play a positive role in melting into the weld seam and increasing the weld penetration. The most probable mechanism of A-TIG welding with fly ash and 40% SiO2 as active fluxes is arc contraction theory. Whereas element Al has high content and dissolves deeply in the welding and other phases in fly ash are very complicated, many other theories could also cause the increasing of the weld penetration, such as various phases interact and release heat with the effect of high temperature arc leading to the increase of arc＆#39; s heat input, other phases in fly ash change the temperature gradient of surface tension in the weld pool.