Influence Of Laser Welding Process On The Quality Of Fe-Ni Alloy Weld Bead

Fe-Ni (36wt.%) alloy is widely used in industrial production because of its very low thermal expansion coefficient between room temperature to230℃and good plasticity. With the development of science and technology, the application fields of this alloy has turned from traditional precision device to electronic industry gradually. Based on the significant application background of Fe-Ni (36wt.%) alloy, it is very essential to investigate its weldability. The welding hot crack is easy to form when the traditional processing method was performed (e.g. TIG, MIG). The improvement solution which could resist high cracking sensitive of Fe-Ni (36wt.%) alloy (e.g. the addition of other elements) usually has a negative effect on its low expansion characteristic. Previous studies had shown when the heat input is kept sufficiently low or the cooling rate is relatively high, the welding crack could be restrained. Therefore, the contradiction between high cracking sensitive and low thermal expansion coefficient can be solved when a suitable welding method is used. Based on the superiority of laser welding and the welding characteristic of Fe-Ni (36wt.%) alloy, an investigation about laser welding of this alloy was carried out in this paper with a Nd:YAG laser. The specific work presented as follows:The analysis and improvement of welding porosity:Preliminary experiments on the weldability of Fe-Ni (36wt.%) alloy suggested the porosity was extremely easy to occur. Furthermore, the effect of welding parameters on the porosity and the characteristic of the porosity/the weld bead with them were studied. The formation mechanism of the porosity was deduced using EDS method to analyze element content and previous studies in combination. On the basis of formation mechanism, the measures for improving the process were put forward.The influence of welding parameters on the morphology of weld bead and the testing of butt welding joint:After the welding porosity was improved, the further research on weld bead was carried out, including:(1) Continuous wave laser bead-on-platc welding experiments. The bead-on-plate experiments were conducted with one-way experimental method based on the parameters designed before. The morphology of the cross section was analyzed by optical microscope. The influence of welding parameters on the morphology was studied.(2) The comparative analysis between CW and pulsed laser bead-on-plate welding experiments. The bead-on-plate experiments on Fe-Ni (36wt.%) alloy were conducted with one-way experimental method by adopting pulsed laser welding method. The influence of pulsed laser parameters on the morphology was analyzed. The major cause of the difference in weld bead by using different modulated laser output was studied.(3) The analysis and testing of butt welding joint. The proper process parameters were applied to butt welding for2mm Fe-Ni (36wt.%) alloy plates. The microstructure, mechanical property and thermal expansion coefficient of butt welding joints were tested. The differences of the results obtained between welding joint and base metal were analyzed and discussed. All these work would provide reference to the application of Fe-Ni (36wt.%) alloy.