Изучение структуры и свойств соединений разнородных материалов, полученных лазерной сваркой

Dissimilar welding is a prospective research field. Such techniques can allow to combine advantages of several materials in productive and easy automatized way. But as a rule, there are challenging problems related to brittle intermetallic compounds formation and thermal properties differences. Ti/Al hybrid structures are of interest for such industry fields where structure mass has the same importance as its durability and strength. Such fields are aircraft and space industry. Despite the importance of such structures classical weld joints of Ti and Al alloys have low ductility due to intermetallic compounds formation. Together with significant differences in melting point, thermal conductivity and thermal expansion of these materials, it leads to low strength and cold cracks formation in these joints. This work provides a study of processes which occur during dissimilar laser welding of Ti and Al-Li alloys. Both cases when the melts of the alloys interacted with each other and when melted Al interacted with solid Ti (welding-brazing) were considered. Such weld formation modes were achieved via laser beam focus displacement towards the Ti plates of several displacement values. To achieve the goal tensile tests, structural study and synchrotron radiation diffraction analysis were carried out. The first chapter provides literature review on existing patents and scientific publications on dissimilar welding for Ti/Al and other metal couples. In this chapter it was concluded that the processes occurring during mixing of melts remain unexplored enough in Ti/Al welding. Based on this the purpose of this work was formylated as to determine the processes that occur during dissimilar laser welding of titanium and aluminum-lithium alloys The second chapter describes the study procedures which were executed in this study. Also, this chapter contains the description of the experimental procedure. The third chapter presents the research results and their analysis. It was found that the laser focus displacement positively influences strength of the joints increasing it from 76 MPa (when welded without the beam displacement) to 168 MPa (for the displacement of 1 mm). Structural study showed that insufficient displacement leads to thick (~800 µm) intermetallic layer formation which consist of α2Ti3Al, γTiAl and β2Ti. Welding with sufficient beam displacement aloud to avoid the alloys melts interaction. Instead of this the joint formed via interaction between Al melt and solid Ti. In this case a thin (~2 µm) TiAl3 intermetallic layer was formed. It is also important that in all cases melting and subsequent crystallization of Al alloy led to its softening in such zones. Because of this such joints cannot reach the base Al alloy strength even when intermetallic layer formation was suppressed. The fourth chapter describes labor and environmental protection features in the laboratory at which this study was performed The last chapter provides the economy calculations of present study. It was fount that this work took 56651.9 rubles to be performed. This paper contains 73 pages, 35 pictures, 9 tables, 1 appendix and also it refers to 64 literature sources.