摘要
The main objective of this investigation is to study the influence of arc constriction current frequency(ACCF)on tensile properties and microstructural evolution of aerospace Alloy 718 sheets(2 mm in thickness)joined by constricted arc TIG(CA-TIG)welding process.One variable at a time approach of design of experiments(DOE)was used,in which ACCF was varied from 4 to 20 kHz at an interval of 5 levels while other parameters were kept constant.The joints welded using ACCF of 4 kHz exhibited superior tensile properties extending joint efficiency up to 99.20%.It is attributed to the grain refinement in fusion zone leading to the evolution of finer,discrete Laves phase in interdendritic areas.An increase of ACCF above 12 kHz caused severe grain growth and evolution of coarser Laves phase in fusion zone.Alloy 718 welds showed more obvious tendency for Nb segregation and Laves phase formation at higher levels of ACCF due to the slower cooling rate.The volume fraction of Laves phase was increased by 62.31%at ACCF of 20 kHz compared to that at 4 kHz,thereby reducing the tensile properties of joints.This is mainly due to the stacking of heat input in weld thermal cycles at increased levels of ACCF.
研究电弧收缩电流频率(ACCF)对收缩电弧钨极氩弧焊(CA-TIG)焊接航空航天718合金板(厚度为2 mm)拉伸性能和显微组织演变的影响。实验设计每次一个变量,即采用从4 kHz到20 kHz之间5个不同的ACCF,其他参数保持不变。结果显示,采用4 kHz ACCF的接头具有良好的拉伸性能,焊接效率可达99.20%。这是由于熔化区的晶粒细化导致枝晶间析出更细小、离散的Laves相。ACCF高于12 kHz时熔化区发生严重晶粒长大和粗大Laves相演变。718合金焊缝在较高的ACCF下由于冷却速度较慢,Nb偏析和Laves相形成的趋势更明显。当ACCF为20 kHz时,Laves相的体积分数比4 kHz时提高62.31%,因此,接头的拉伸性能降低。这主要是由于当ACCF增加时,焊接热循环中热输入的叠加。
基金
This work was supported by the Indian Space Research Organization(ISRO),Department of Space,India,under ISRO RESPOND scheme(Project No.ISRO/RES/3/728/16-17).
